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The discussion section of a research paper is where the author analyzes and explains the importance of the study's results. It presents the conclusions drawn from the study, compares them to previous research, and addresses any potential limitations or weaknesses. The discussion section should also suggest areas for future research.

Everything is not that complicated if you know where to find the required information. We’ll tell you everything there is to know about writing your discussion. Our easy guide covers all important bits, including research questions and your research results. Do you know how all enumerated events are connected? Well, you will after reading this guide we’ve prepared for you!

What Is in the Discussion Section of a Research Paper

The discussion section of a research paper can be viewed as something similar to the conclusion of your paper. But not literal, of course. It’s an ultimate section where you can talk about the findings of your study. Think about these questions when writing:

• Did you answer all of the promised research questions?
• Did you mention why your work matters?
• What are your findings, and why should anyone even care?
• Does your study have a literature review?

So, answer your questions, provide proof, and don’t forget about your promises from the introduction. 

How to Write a Discussion Section in 5 Steps

How to write the discussion section of a research paper is something everyone googles eventually. It's just life. But why not make everything easier? In brief, this section we’re talking about must include all following parts:

• Answers for research questions
• Literature review
• Results of the work
• Limitations of one’s study
• Overall conclusion

Indeed, all those parts may confuse anyone. So by looking at our guide, you'll save yourself some hassle.  P.S. All our steps are easy and explained in detail! But if you are looking for the most efficient solution, consider using professional help. Leave your “ write my research paper for me ” order at StudyCrumb and get a customized study tailored to your requirements.

Step 1. Start Strong: Discussion Section of a Research Paper

First and foremost, how to start the discussion section of a research paper? Here’s what you should definitely consider before settling down to start writing:

• All essays or papers must begin strong. All readers will not wait for any writer to get to the point. We advise summarizing the paper's main findings.
• Moreover, you should relate both discussion and literature review to what you have discovered. Mentioning that would be a plus too.
• Make sure that an introduction or start per se is clear and concise. Word count might be needed for school. But any paper should be understandable and not too diluted.

Step 2. Answer the Questions in Your Discussion Section of a Research Paper

Writing the discussion section of a research paper also involves mentioning your questions. Remember that in your introduction, you have promised your readers to answer certain questions. Well, now it’s a perfect time to finally give the awaited answer. You need to explain all possible correlations between your findings, research questions, and literature proposed. You already had hypotheses. So were they correct, or maybe you want to propose certain corrections? Section’s main goal is to avoid open ends. It’s not a story or a fairytale with an intriguing ending. If you have several questions, you must answer them. As simple as that.

Step 3. Relate Your Results in a Discussion Section

Writing a discussion section of a research paper also requires any writer to explain their results. You will undoubtedly include an impactful literature review. However, your readers should not just try and struggle with understanding what are some specific relationships behind previous studies and your results.  Your results should sound something like: “This guy in their paper discovered that apples are green. Nevertheless, I have proven via experimentation and research that apples are actually red.” Please, don’t take these results directly. It’s just an initial hypothesis. But what you should definitely remember is any practical implications of your study. Why does it matter and how can anyone use it? That’s the most crucial question.

Step 4. Describe the Limitations in Your Discussion Section

Discussion section of a research paper isn’t limitless. What does that mean? Essentially, it means that you also have to discuss any limitations of your study. Maybe you had some methodological inconsistencies. Possibly, there are no particular theories or not enough information for you to be entirely confident in one’s conclusions.  You might say that an available source of literature you have studied does not focus on one’s issue. That’s why one’s main limitation is theoretical. However, keep in mind that your limitations must possess a certain degree of relevancy. You can just say that you haven’t found enough books. Your information must be truthful to research.

Step 5. Conclude Your Discussion Section With Recommendations

Your last step when you write a discussion section in a paper is its conclusion, like in any other academic work. Writer’s conclusion must be as strong as their starting point of the overall work. Check out our brief list of things to know about the conclusion in research paper :

• It must present its scientific relevance and importance of your work.
• It should include different implications of your research.
• It should not, however, discuss anything new or things that you have not mentioned before.
• Leave no open questions and carefully complete the work without them.

Discussion Section of a Research Paper Example

All the best example discussion sections of a research paper will be written according to our brief guide. Don’t forget that you need to state your findings and underline the importance of your work. An undoubtedly big part of one’s discussion will definitely be answering and explaining the research questions. In other words, you’ll already have all the knowledge you have so carefully gathered. Our last step for you is to recollect and wrap up your paper. But we’re sure you’ll succeed!

How to Write a Discussion Section: Final Thoughts

Today we have covered how to write a discussion section. That was quite a brief journey, wasn’t it? Just to remind you to focus on these things:

• Importance of your study.
• Summary of the information you have gathered.
• Main findings and conclusions.
• Answers to all research questions without an open end.
• Correlation between literature review and your results.

But, wait, this guide is not the only thing we can do. Looking for how to write an abstract for a research paper  for example? We have such a blog and much more on our platform.

Our academic writing service is just a click away. We are proud to say that our writers are professionals in their fields. Buy a research paper and our experts can provide prompt solutions without compromising the quality.

Discussion Section of a Research Paper: Frequently Asked Questions

1. how long should the discussion section of a research paper be.

Our discussion section of a research paper should not be longer than other sections. So try to keep it short but as informative as possible. It usually contains around 6-7 paragraphs in length. It is enough to briefly summarize all the important data and not to drag it.

2. What's the difference between the discussion and the results?

The difference between discussion and results is very simple and easy to understand. The results only report your main findings. You stated what you have found and how you have done that. In contrast, one’s discussion mentions your findings and explains how they relate to other literature, research questions, and one’s hypothesis. Therefore, it is not only a report but an efficient as well as proper explanation.

3. What's the difference between a discussion and a conclusion?

The difference between discussion and conclusion is also quite easy. Conclusion is a brief summary of all the findings and results. Still, our favorite discussion section interprets and explains your main results. It is an important but more lengthy and wordy part. Besides, it uses extra literature for references.

4. What is the purpose of the discussion section?

The primary purpose of a discussion section is to interpret and describe all your interesting findings. Therefore, you should state what you have learned, whether your hypothesis was correct and how your results can be explained using other sources. If this section is clear to readers, our congratulations as you have succeeded.

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• How to Write Discussions and Conclusions

The discussion section contains the results and outcomes of a study. An effective discussion informs readers what can be learned from your experiment and provides context for the results.

What makes an effective discussion?

When you’re ready to write your discussion, you’ve already introduced the purpose of your study and provided an in-depth description of the methodology. The discussion informs readers about the larger implications of your study based on the results. Highlighting these implications while not overstating the findings can be challenging, especially when you’re submitting to a journal that selects articles based on novelty or potential impact. Regardless of what journal you are submitting to, the discussion section always serves the same purpose: concluding what your study results actually mean.

A successful discussion section puts your findings in context. It should include:

• the results of your research,
• a discussion of related research, and
• a comparison between your results and initial hypothesis.

Tip: Not all journals share the same naming conventions.

You can apply the advice in this article to the conclusion, results or discussion sections of your manuscript.

Our Early Career Researcher community tells us that the conclusion is often considered the most difficult aspect of a manuscript to write. To help, this guide provides questions to ask yourself, a basic structure to model your discussion off of and examples from published manuscripts. 

Questions to ask yourself:

• Was my hypothesis correct?
• If my hypothesis is partially correct or entirely different, what can be learned from the results? 
• How do the conclusions reshape or add onto the existing knowledge in the field? What does previous research say about the topic? 
• Why are the results important or relevant to your audience? Do they add further evidence to a scientific consensus or disprove prior studies? 
• How can future research build on these observations? What are the key experiments that must be done? 
• What is the “take-home” message you want your reader to leave with?

How to structure a discussion

Trying to fit a complete discussion into a single paragraph can add unnecessary stress to the writing process. If possible, you’ll want to give yourself two or three paragraphs to give the reader a comprehensive understanding of your study as a whole. Here’s one way to structure an effective discussion:

Writing Tips

While the above sections can help you brainstorm and structure your discussion, there are many common mistakes that writers revert to when having difficulties with their paper. Writing a discussion can be a delicate balance between summarizing your results, providing proper context for your research and avoiding introducing new information. Remember that your paper should be both confident and honest about the results! 

• Read the journal’s guidelines on the discussion and conclusion sections. If possible, learn about the guidelines before writing the discussion to ensure you’re writing to meet their expectations. 
• Begin with a clear statement of the principal findings. This will reinforce the main take-away for the reader and set up the rest of the discussion. 
• Explain why the outcomes of your study are important to the reader. Discuss the implications of your findings realistically based on previous literature, highlighting both the strengths and limitations of the research. 
• State whether the results prove or disprove your hypothesis. If your hypothesis was disproved, what might be the reasons? 
• Introduce new or expanded ways to think about the research question. Indicate what next steps can be taken to further pursue any unresolved questions. 
• If dealing with a contemporary or ongoing problem, such as climate change, discuss possible consequences if the problem is avoided. 
• Be concise. Adding unnecessary detail can distract from the main findings. 

Don’t

• Rewrite your abstract. Statements with “we investigated” or “we studied” generally do not belong in the discussion. 
• Include new arguments or evidence not previously discussed. Necessary information and evidence should be introduced in the main body of the paper. 
• Apologize. Even if your research contains significant limitations, don’t undermine your authority by including statements that doubt your methodology or execution. 
• Shy away from speaking on limitations or negative results. Including limitations and negative results will give readers a complete understanding of the presented research. Potential limitations include sources of potential bias, threats to internal or external validity, barriers to implementing an intervention and other issues inherent to the study design. 
• Overstate the importance of your findings. Making grand statements about how a study will fully resolve large questions can lead readers to doubt the success of the research. 

Snippets of Effective Discussions:

Consumer-based actions to reduce plastic pollution in rivers: A multi-criteria decision analysis approach

Identifying reliable indicators of fitness in polar bears

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The purpose of the discussion section is to interpret and describe the significance of your findings in relation to what was already known about the research problem being investigated and to explain any new understanding or insights that emerged as a result of your research. The discussion will always connect to the introduction by way of the research questions or hypotheses you posed and the literature you reviewed, but the discussion does not simply repeat or rearrange the first parts of your paper; the discussion clearly explains how your study advanced the reader's understanding of the research problem from where you left them at the end of your review of prior research.

Annesley, Thomas M. “The Discussion Section: Your Closing Argument.” Clinical Chemistry 56 (November 2010): 1671-1674.

Importance of a Good Discussion

The discussion section is often considered the most important part of your research paper because it:

• Most effectively demonstrates your ability as a researcher to think critically about an issue, to develop creative solutions to problems based upon a logical synthesis of the findings, and to formulate a deeper, more profound understanding of the research problem under investigation;
• Presents the underlying meaning of your research, notes possible implications in other areas of study, and explores possible improvements that can be made in order to further develop the concerns of your research;
• Highlights the importance of your study and how it can contribute to understanding the research problem within the field of study;
• Presents how the findings from your study revealed and helped fill gaps in the literature that had not been previously exposed or adequately described; and,
• Engages the reader in thinking critically about issues based on an evidence-based interpretation of findings; it is not governed strictly by objective reporting of information.

Annesley Thomas M. “The Discussion Section: Your Closing Argument.” Clinical Chemistry 56 (November 2010): 1671-1674; Bitchener, John and Helen Basturkmen. “Perceptions of the Difficulties of Postgraduate L2 Thesis Students Writing the Discussion Section.” Journal of English for Academic Purposes 5 (January 2006): 4-18; Kretchmer, Paul. Fourteen Steps to Writing an Effective Discussion Section. San Francisco Edit, 2003-2008.

Structure and Writing Style

I.  General Rules

These are the general rules you should adopt when composing your discussion of the results :

• Do not be verbose or repetitive; be concise and make your points clearly
• Avoid the use of jargon or undefined technical language
• Follow a logical stream of thought; in general, interpret and discuss the significance of your findings in the same sequence you described them in your results section [a notable exception is to begin by highlighting an unexpected result or a finding that can grab the reader's attention]
• Use the present verb tense, especially for established facts; however, refer to specific works or prior studies in the past tense
• If needed, use subheadings to help organize your discussion or to categorize your interpretations into themes

II.  The Content

The content of the discussion section of your paper most often includes :

• Explanation of results : Comment on whether or not the results were expected for each set of findings; go into greater depth to explain findings that were unexpected or especially profound. If appropriate, note any unusual or unanticipated patterns or trends that emerged from your results and explain their meaning in relation to the research problem.
• References to previous research : Either compare your results with the findings from other studies or use the studies to support a claim. This can include re-visiting key sources already cited in your literature review section, or, save them to cite later in the discussion section if they are more important to compare with your results instead of being a part of the general literature review of prior research used to provide context and background information. Note that you can make this decision to highlight specific studies after you have begun writing the discussion section.
• Deduction : A claim for how the results can be applied more generally. For example, describing lessons learned, proposing recommendations that can help improve a situation, or highlighting best practices.
• Hypothesis : A more general claim or possible conclusion arising from the results [which may be proved or disproved in subsequent research]. This can be framed as new research questions that emerged as a consequence of your analysis.

III.  Organization and Structure

Keep the following sequential points in mind as you organize and write the discussion section of your paper:

• Think of your discussion as an inverted pyramid. Organize the discussion from the general to the specific, linking your findings to the literature, then to theory, then to practice [if appropriate].
• Use the same key terms, narrative style, and verb tense [present] that you used when describing the research problem in your introduction.
• Begin by briefly re-stating the research problem you were investigating and answer all of the research questions underpinning the problem that you posed in the introduction.
• Describe the patterns, principles, and relationships shown by each major findings and place them in proper perspective. The sequence of this information is important; first state the answer, then the relevant results, then cite the work of others. If appropriate, refer the reader to a figure or table to help enhance the interpretation of the data [either within the text or as an appendix].
• Regardless of where it's mentioned, a good discussion section includes analysis of any unexpected findings. This part of the discussion should begin with a description of the unanticipated finding, followed by a brief interpretation as to why you believe it appeared and, if necessary, its possible significance in relation to the overall study. If more than one unexpected finding emerged during the study, describe each of them in the order they appeared as you gathered or analyzed the data. As noted, the exception to discussing findings in the same order you described them in the results section would be to begin by highlighting the implications of a particularly unexpected or significant finding that emerged from the study, followed by a discussion of the remaining findings.
• Before concluding the discussion, identify potential limitations and weaknesses if you do not plan to do so in the conclusion of the paper. Comment on their relative importance in relation to your overall interpretation of the results and, if necessary, note how they may affect the validity of your findings. Avoid using an apologetic tone; however, be honest and self-critical [e.g., in retrospect, had you included a particular question in a survey instrument, additional data could have been revealed].
• The discussion section should end with a concise summary of the principal implications of the findings regardless of their significance. Give a brief explanation about why you believe the findings and conclusions of your study are important and how they support broader knowledge or understanding of the research problem. This can be followed by any recommendations for further research. However, do not offer recommendations which could have been easily addressed within the study. This would demonstrate to the reader that you have inadequately examined and interpreted the data.

IV.  Overall Objectives

The objectives of your discussion section should include the following: I.  Reiterate the Research Problem/State the Major Findings

Briefly reiterate the research problem or problems you are investigating and the methods you used to investigate them, then move quickly to describe the major findings of the study. You should write a direct, declarative, and succinct proclamation of the study results, usually in one paragraph.

II.  Explain the Meaning of the Findings and Why They are Important

No one has thought as long and hard about your study as you have. Systematically explain the underlying meaning of your findings and state why you believe they are significant. After reading the discussion section, you want the reader to think critically about the results and why they are important. You don’t want to force the reader to go through the paper multiple times to figure out what it all means. If applicable, begin this part of the section by repeating what you consider to be your most significant or unanticipated finding first, then systematically review each finding. Otherwise, follow the general order you reported the findings presented in the results section.

III.  Relate the Findings to Similar Studies

No study in the social sciences is so novel or possesses such a restricted focus that it has absolutely no relation to previously published research. The discussion section should relate your results to those found in other studies, particularly if questions raised from prior studies served as the motivation for your research. This is important because comparing and contrasting the findings of other studies helps to support the overall importance of your results and it highlights how and in what ways your study differs from other research about the topic. Note that any significant or unanticipated finding is often because there was no prior research to indicate the finding could occur. If there is prior research to indicate this, you need to explain why it was significant or unanticipated. IV.  Consider Alternative Explanations of the Findings

It is important to remember that the purpose of research in the social sciences is to discover and not to prove . When writing the discussion section, you should carefully consider all possible explanations for the study results, rather than just those that fit your hypothesis or prior assumptions and biases. This is especially important when describing the discovery of significant or unanticipated findings.

V.  Acknowledge the Study’s Limitations

It is far better for you to identify and acknowledge your study’s limitations than to have them pointed out by your professor! Note any unanswered questions or issues your study could not address and describe the generalizability of your results to other situations. If a limitation is applicable to the method chosen to gather information, then describe in detail the problems you encountered and why. VI.  Make Suggestions for Further Research

You may choose to conclude the discussion section by making suggestions for further research [as opposed to offering suggestions in the conclusion of your paper]. Although your study can offer important insights about the research problem, this is where you can address other questions related to the problem that remain unanswered or highlight hidden issues that were revealed as a result of conducting your research. You should frame your suggestions by linking the need for further research to the limitations of your study [e.g., in future studies, the survey instrument should include more questions that ask..."] or linking to critical issues revealed from the data that were not considered initially in your research.

NOTE: Besides the literature review section, the preponderance of references to sources is usually found in the discussion section . A few historical references may be helpful for perspective, but most of the references should be relatively recent and included to aid in the interpretation of your results, to support the significance of a finding, and/or to place a finding within a particular context. If a study that you cited does not support your findings, don't ignore it--clearly explain why your research findings differ from theirs.

V.  Problems to Avoid

• Do not waste time restating your results . Should you need to remind the reader of a finding to be discussed, use "bridge sentences" that relate the result to the interpretation. An example would be: “In the case of determining available housing to single women with children in rural areas of Texas, the findings suggest that access to good schools is important...," then move on to further explaining this finding and its implications.
• As noted, recommendations for further research can be included in either the discussion or conclusion of your paper, but do not repeat your recommendations in the both sections. Think about the overall narrative flow of your paper to determine where best to locate this information. However, if your findings raise a lot of new questions or issues, consider including suggestions for further research in the discussion section.
• Do not introduce new results in the discussion section. Be wary of mistaking the reiteration of a specific finding for an interpretation because it may confuse the reader. The description of findings [results section] and the interpretation of their significance [discussion section] should be distinct parts of your paper. If you choose to combine the results section and the discussion section into a single narrative, you must be clear in how you report the information discovered and your own interpretation of each finding. This approach is not recommended if you lack experience writing college-level research papers.
• Use of the first person pronoun is generally acceptable. Using first person singular pronouns can help emphasize a point or illustrate a contrasting finding. However, keep in mind that too much use of the first person can actually distract the reader from the main points [i.e., I know you're telling me this--just tell me!].

Analyzing vs. Summarizing. Department of English Writing Guide. George Mason University; Discussion. The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. Department of Biology. Bates College; Hess, Dean R. "How to Write an Effective Discussion." Respiratory Care 49 (October 2004); Kretchmer, Paul. Fourteen Steps to Writing to Writing an Effective Discussion Section. San Francisco Edit, 2003-2008; The Lab Report. University College Writing Centre. University of Toronto; Sauaia, A. et al. "The Anatomy of an Article: The Discussion Section: "How Does the Article I Read Today Change What I Will Recommend to my Patients Tomorrow?” The Journal of Trauma and Acute Care Surgery 74 (June 2013): 1599-1602; Research Limitations & Future Research . Lund Research Ltd., 2012; Summary: Using it Wisely. The Writing Center. University of North Carolina; Schafer, Mickey S. Writing the Discussion. Writing in Psychology course syllabus. University of Florida; Yellin, Linda L. A Sociology Writer's Guide . Boston, MA: Allyn and Bacon, 2009.

Writing Tip

Don’t Over-Interpret the Results!

Interpretation is a subjective exercise. As such, you should always approach the selection and interpretation of your findings introspectively and to think critically about the possibility of judgmental biases unintentionally entering into discussions about the significance of your work. With this in mind, be careful that you do not read more into the findings than can be supported by the evidence you have gathered. Remember that the data are the data: nothing more, nothing less.

MacCoun, Robert J. "Biases in the Interpretation and Use of Research Results." Annual Review of Psychology 49 (February 1998): 259-287.

Another Writing Tip

Don't Write Two Results Sections!

One of the most common mistakes that you can make when discussing the results of your study is to present a superficial interpretation of the findings that more or less re-states the results section of your paper. Obviously, you must refer to your results when discussing them, but focus on the interpretation of those results and their significance in relation to the research problem, not the data itself.

Azar, Beth. "Discussing Your Findings."  American Psychological Association gradPSYCH Magazine (January 2006).

Yet Another Writing Tip

Avoid Unwarranted Speculation!

The discussion section should remain focused on the findings of your study. For example, if the purpose of your research was to measure the impact of foreign aid on increasing access to education among disadvantaged children in Bangladesh, it would not be appropriate to speculate about how your findings might apply to populations in other countries without drawing from existing studies to support your claim or if analysis of other countries was not a part of your original research design. If you feel compelled to speculate, do so in the form of describing possible implications or explaining possible impacts. Be certain that you clearly identify your comments as speculation or as a suggestion for where further research is needed. Sometimes your professor will encourage you to expand your discussion of the results in this way, while others don’t care what your opinion is beyond your effort to interpret the data in relation to the research problem.

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Writing a scientific paper.

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• INTRODUCTION

Writing a "good" discussion section

"discussion and conclusions checklist" from: how to write a good scientific paper. chris a. mack. spie. 2018., peer review.

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This is is usually the hardest section to write. You are trying to bring out the true meaning of your data without being too long. Do not use words to conceal your facts or reasoning. Also do not repeat your results, this is a discussion.

• Present principles, relationships and generalizations shown by the results
• Point out exceptions or lack of correlations. Define why you think this is so.
• Show how your results agree or disagree with previously published works
• Discuss the theoretical implications of your work as well as practical applications
• State your conclusions clearly. Summarize your evidence for each conclusion.
• Discuss the significance of the results
•  Evidence does not explain itself; the results must be presented and then explained.
• Typical stages in the discussion: summarizing the results, discussing whether results are expected or unexpected, comparing these results to previous work, interpreting and explaining the results (often by comparison to a theory or model), and hypothesizing about their generality.
• Discuss any problems or shortcomings encountered during the course of the work.
• Discuss possible alternate explanations for the results.
• Avoid: presenting results that are never discussed; presenting discussion that does not relate to any of the results; presenting results and discussion in chronological order rather than logical order; ignoring results that do not support the conclusions; drawing conclusions from results without logical arguments to back them up. 

CONCLUSIONS

• Provide a very brief summary of the Results and Discussion.
• Emphasize the implications of the findings, explaining how the work is significant and providing the key message(s) the author wishes to convey.
• Provide the most general claims that can be supported by the evidence.
• Provide a future perspective on the work.
• Avoid: repeating the abstract; repeating background information from the Introduction; introducing new evidence or new arguments not found in the Results and Discussion; repeating the arguments made in the Results and Discussion; failing to address all of the research questions set out in the Introduction. 

WHAT HAPPENS AFTER I COMPLETE MY PAPER?

 The peer review process is the quality control step in the publication of ideas.  Papers that are submitted to a journal for publication are sent out to several scientists (peers) who look carefully at the paper to see if it is "good science".  These reviewers then recommend to the editor of a journal whether or not a paper should be published. Most journals have publication guidelines. Ask for them and follow them exactly.    Peer reviewers examine the soundness of the materials and methods section.  Are the materials and methods used written clearly enough for another scientist to reproduce the experiment?  Other areas they look at are: originality of research, significance of research question studied, soundness of the discussion and interpretation, correct spelling and use of technical terms, and length of the article.

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How to Write a Discussion Section for a Research Paper

We’ve talked about several useful writing tips that authors should consider while drafting or editing their research papers. In particular, we’ve focused on  figures and legends , as well as the Introduction ,  Methods , and  Results . Now that we’ve addressed the more technical portions of your journal manuscript, let’s turn to the analytical segments of your research article. In this article, we’ll provide tips on how to write a strong Discussion section that best portrays the significance of your research contributions.

What is the Discussion section of a research paper?

In a nutshell,  your Discussion fulfills the promise you made to readers in your Introduction . At the beginning of your paper, you tell us why we should care about your research. You then guide us through a series of intricate images and graphs that capture all the relevant data you collected during your research. We may be dazzled and impressed at first, but none of that matters if you deliver an anti-climactic conclusion in the Discussion section!

Are you feeling pressured? Don’t worry. To be honest, you will edit the Discussion section of your manuscript numerous times. After all, in as little as one to two paragraphs ( Nature ‘s suggestion  based on their 3,000-word main body text limit), you have to explain how your research moves us from point A (issues you raise in the Introduction) to point B (our new understanding of these matters). You must also recommend how we might get to point C (i.e., identify what you think is the next direction for research in this field). That’s a lot to say in two paragraphs!

So, how do you do that? Let’s take a closer look.

What should I include in the Discussion section?

As we stated above, the goal of your Discussion section is to  answer the questions you raise in your Introduction by using the results you collected during your research . The content you include in the Discussions segment should include the following information:

• Remind us why we should be interested in this research project.
• Describe the nature of the knowledge gap you were trying to fill using the results of your study.
• Don’t repeat your Introduction. Instead, focus on why  this  particular study was needed to fill the gap you noticed and why that gap needed filling in the first place.
• Mainly, you want to remind us of how your research will increase our knowledge base and inspire others to conduct further research.
• Clearly tell us what that piece of missing knowledge was.
• Answer each of the questions you asked in your Introduction and explain how your results support those conclusions.
• Make sure to factor in all results relevant to the questions (even if those results were not statistically significant).
• Focus on the significance of the most noteworthy results.
• If conflicting inferences can be drawn from your results, evaluate the merits of all of them.
• Don’t rehash what you said earlier in the Results section. Rather, discuss your findings in the context of answering your hypothesis. Instead of making statements like “[The first result] was this…,” say, “[The first result] suggests [conclusion].”
• Do your conclusions line up with existing literature?
• Discuss whether your findings agree with current knowledge and expectations.
• Keep in mind good persuasive argument skills, such as explaining the strengths of your arguments and highlighting the weaknesses of contrary opinions.
• If you discovered something unexpected, offer reasons. If your conclusions aren’t aligned with current literature, explain.
• Address any limitations of your study and how relevant they are to interpreting your results and validating your findings.
• Make sure to acknowledge any weaknesses in your conclusions and suggest room for further research concerning that aspect of your analysis.
• Make sure your suggestions aren’t ones that should have been conducted during your research! Doing so might raise questions about your initial research design and protocols.
• Similarly, maintain a critical but unapologetic tone. You want to instill confidence in your readers that you have thoroughly examined your results and have objectively assessed them in a way that would benefit the scientific community’s desire to expand our knowledge base.
• Recommend next steps.
• Your suggestions should inspire other researchers to conduct follow-up studies to build upon the knowledge you have shared with them.
• Keep the list short (no more than two).

How to Write the Discussion Section

The above list of what to include in the Discussion section gives an overall idea of what you need to focus on throughout the section. Below are some tips and general suggestions about the technical aspects of writing and organization that you might find useful as you draft or revise the contents we’ve outlined above.

Technical writing elements

• Embrace active voice because it eliminates the awkward phrasing and wordiness that accompanies passive voice.
• Use the present tense, which should also be employed in the Introduction.
• Sprinkle with first person pronouns if needed, but generally, avoid it. We want to focus on your findings.
• Maintain an objective and analytical tone.

Discussion section organization

• Keep the same flow across the Results, Methods, and Discussion sections.
• We develop a rhythm as we read and parallel structures facilitate our comprehension. When you organize information the same way in each of these related parts of your journal manuscript, we can quickly see how a certain result was interpreted and quickly verify the particular methods used to produce that result.
• Notice how using parallel structure will eliminate extra narration in the Discussion part since we can anticipate the flow of your ideas based on what we read in the Results segment. Reducing wordiness is important when you only have a few paragraphs to devote to the Discussion section!
• Within each subpart of a Discussion, the information should flow as follows: (A) conclusion first, (B) relevant results and how they relate to that conclusion and (C) relevant literature.
• End with a concise summary explaining the big-picture impact of your study on our understanding of the subject matter. At the beginning of your Discussion section, you stated why  this  particular study was needed to fill the gap you noticed and why that gap needed filling in the first place. Now, it is time to end with “how your research filled that gap.”

Discussion Part 1: Summarizing Key Findings

Begin the Discussion section by restating your  statement of the problem  and briefly summarizing the major results. Do not simply repeat your findings. Rather, try to create a concise statement of the main results that directly answer the central research question that you stated in the Introduction section . This content should not be longer than one paragraph in length.

Many researchers struggle with understanding the precise differences between a Discussion section and a Results section . The most important thing to remember here is that your Discussion section should subjectively evaluate the findings presented in the Results section, and in relatively the same order. Keep these sections distinct by making sure that you do not repeat the findings without providing an interpretation.

Phrase examples: Summarizing the results

• The findings indicate that …
• These results suggest a correlation between A and B …
• The data present here suggest that …
• An interpretation of the findings reveals a connection between…

Discussion Part 2: Interpreting the Findings

What do the results mean? It may seem obvious to you, but simply looking at the figures in the Results section will not necessarily convey to readers the importance of the findings in answering your research questions.

The exact structure of interpretations depends on the type of research being conducted. Here are some common approaches to interpreting data:

• Identifying correlations and relationships in the findings
• Explaining whether the results confirm or undermine your research hypothesis
• Giving the findings context within the history of similar research studies
• Discussing unexpected results and analyzing their significance to your study or general research
• Offering alternative explanations and arguing for your position

Organize the Discussion section around key arguments, themes, hypotheses, or research questions or problems. Again, make sure to follow the same order as you did in the Results section.

Discussion Part 3: Discussing the Implications

In addition to providing your own interpretations, show how your results fit into the wider scholarly literature you surveyed in the  literature review section. This section is called the implications of the study . Show where and how these results fit into existing knowledge, what additional insights they contribute, and any possible consequences that might arise from this knowledge, both in the specific research topic and in the wider scientific domain.

Questions to ask yourself when dealing with potential implications:

• Do your findings fall in line with existing theories, or do they challenge these theories or findings? What new information do they contribute to the literature, if any? How exactly do these findings impact or conflict with existing theories or models?
• What are the practical implications on actual subjects or demographics?
• What are the methodological implications for similar studies conducted either in the past or future?

Your purpose in giving the implications is to spell out exactly what your study has contributed and why researchers and other readers should be interested.

Phrase examples: Discussing the implications of the research

• These results confirm the existing evidence in X studies…
• The results are not in line with the foregoing theory that…
• This experiment provides new insights into the connection between…
• These findings present a more nuanced understanding of…
• While previous studies have focused on X, these results demonstrate that Y.

Step 4: Acknowledging the limitations

All research has study limitations of one sort or another. Acknowledging limitations in methodology or approach helps strengthen your credibility as a researcher. Study limitations are not simply a list of mistakes made in the study. Rather, limitations help provide a more detailed picture of what can or cannot be concluded from your findings. In essence, they help temper and qualify the study implications you listed previously.

Study limitations can relate to research design, specific methodological or material choices, or unexpected issues that emerged while you conducted the research. Mention only those limitations directly relate to your research questions, and explain what impact these limitations had on how your study was conducted and the validity of any interpretations.

Possible types of study limitations:

• Insufficient sample size for statistical measurements
• Lack of previous research studies on the topic
• Methods/instruments/techniques used to collect the data
• Limited access to data
• Time constraints in properly preparing and executing the study

After discussing the study limitations, you can also stress that your results are still valid. Give some specific reasons why the limitations do not necessarily handicap your study or narrow its scope.

Phrase examples: Limitations sentence beginners

• “There may be some possible limitations in this study.”
• “The findings of this study have to be seen in light of some limitations.”
•  “The first limitation is the…The second limitation concerns the…”
•  “The empirical results reported herein should be considered in the light of some limitations.”
• “This research, however, is subject to several limitations.”
• “The primary limitation to the generalization of these results is…”
• “Nonetheless, these results must be interpreted with caution and a number of limitations should be borne in mind.”

Discussion Part 5: Giving Recommendations for Further Research

Based on your interpretation and discussion of the findings, your recommendations can include practical changes to the study or specific further research to be conducted to clarify the research questions. Recommendations are often listed in a separate Conclusion section , but often this is just the final paragraph of the Discussion section.

Suggestions for further research often stem directly from the limitations outlined. Rather than simply stating that “further research should be conducted,” provide concrete specifics for how future can help answer questions that your research could not.

Phrase examples: Recommendation sentence beginners

• Further research is needed to establish …
• There is abundant space for further progress in analyzing…
• A further study with more focus on X should be done to investigate…
• Further studies of X that account for these variables must be undertaken.

Consider Receiving Professional Language Editing

As you edit or draft your research manuscript, we hope that you implement these guidelines to produce a more effective Discussion section. And after completing your draft, don’t forget to submit your work to a professional proofreading and English editing service like Wordvice, including our manuscript editing service for  paper editing , cover letter editing , SOP editing , and personal statement proofreading services. Language editors not only proofread and correct errors in grammar, punctuation, mechanics, and formatting but also improve terms and revise phrases so they read more naturally. Wordvice is an industry leader in providing high-quality revision for all types of academic documents.

For additional information about how to write a strong research paper, make sure to check out our full  research writing series !

Wordvice Writing Resources

• How to Write a Research Paper Introduction 
• Which Verb Tenses to Use in a Research Paper
• How to Write an Abstract for a Research Paper
• How to Write a Research Paper Title
• Useful Phrases for Academic Writing
• Common Transition Terms in Academic Papers
• Active and Passive Voice in Research Papers
• 100+ Verbs That Will Make Your Research Writing Amazing
• Tips for Paraphrasing in Research Papers

Additional Academic Resources

•   Guide for Authors.  (Elsevier)
•  How to Write the Results Section of a Research Paper.  (Bates College)
•   Structure of a Research Paper.  (University of Minnesota Biomedical Library)
•   How to Choose a Target Journal  (Springer)
•   How to Write Figures and Tables  (UNC Writing Center)

Organizing Academic Research Papers: 8. The Discussion

• Purpose of Guide
• Design Flaws to Avoid
• Glossary of Research Terms
• Narrowing a Topic Idea
• Broadening a Topic Idea
• Extending the Timeliness of a Topic Idea
• Academic Writing Style
• Choosing a Title
• Making an Outline
• Paragraph Development
• Executive Summary
• Background Information
• The Research Problem/Question
• Theoretical Framework
• Citation Tracking
• Content Alert Services
• Evaluating Sources
• Primary Sources
• Secondary Sources
• Tertiary Sources
• What Is Scholarly vs. Popular?
• Qualitative Methods
• Quantitative Methods
• Using Non-Textual Elements
• Limitations of the Study
• Common Grammar Mistakes
• Avoiding Plagiarism
• Footnotes or Endnotes?
• Further Readings
• Annotated Bibliography
• Dealing with Nervousness
• Using Visual Aids
• Grading Someone Else's Paper
• How to Manage Group Projects
• Multiple Book Review Essay
• Reviewing Collected Essays
• About Informed Consent
• Writing Field Notes
• Writing a Policy Memo
• Writing a Research Proposal
• Acknowledgements

The purpose of the discussion is to interpret and describe the significance of your findings in light of what was already known about the research problem being investigated, and to explain any new understanding or fresh insights about the problem after you've taken the findings into consideration. The discussion will always connect to the introduction by way of the research questions or hypotheses you posed and the literature you reviewed, but it does not simply repeat or rearrange the introduction; the discussion should always explain how your study has moved the reader's understanding of the research problem forward from where you left them at the end of the introduction.

Importance of a Good Discussion

This section is often considered the most important part of a research paper because it most effectively demonstrates your ability as a researcher to think critically about an issue, to develop creative solutions to problems based on the findings, and to formulate a deeper, more profound understanding of the research problem you are studying.

The discussion section is where you explore the underlying meaning of your research , its possible implications in other areas of study, and the possible improvements that can be made in order to further develop the concerns of your research.

This is the section where you need to present the importance of your study and how it may be able to contribute to and/or fill existing gaps in the field. If appropriate, the discussion section is also where you state how the findings from your study revealed new gaps in the literature that had not been previously exposed or adequately described.

This part of the paper is not strictly governed by objective reporting of information but, rather, it is where you can engage in creative thinking about issues through evidence-based interpretation of findings. This is where you infuse your results with meaning.

Kretchmer, Paul. Fourteen Steps to Writing to Writing an Effective Discussion Section . San Francisco Edit, 2003-2008.

Structure and Writing Style

I.  General Rules

These are the general rules you should adopt when composing your discussion of the results :

• Do not be verbose or repetitive.
• Be concise and make your points clearly.
• Avoid using jargon.
• Follow a logical stream of thought.
• Use the present verb tense, especially for established facts; however, refer to specific works and references in the past tense.
• If needed, use subheadings to help organize your presentation or to group your interpretations into themes.

II.  The Content

The content of the discussion section of your paper most often includes :

• Explanation of results : comment on whether or not the results were expected and present explanations for the results; go into greater depth when explaining findings that were unexpected or especially profound. If appropriate, note any unusual or unanticipated patterns or trends that emerged from your results and explain their meaning.
• References to previous research : compare your results with the findings from other studies, or use the studies to support a claim. This can include re-visiting key sources already cited in your literature review section, or, save them to cite later in the discussion section if they are more important to compare with your results than being part of the general research you cited to provide context and background information.
• Deduction : a claim for how the results can be applied more generally. For example, describing lessons learned, proposing recommendations that can help improve a situation, or recommending best practices.
• Hypothesis : a more general claim or possible conclusion arising from the results [which may be proved or disproved in subsequent research].

III. Organization and Structure

Keep the following sequential points in mind as you organize and write the discussion section of your paper:

• Think of your discussion as an inverted pyramid. Organize the discussion from the general to the specific, linking your findings to the literature, then to theory, then to practice [if appropriate].
• Use the same key terms, mode of narration, and verb tense [present] that you used when when describing the research problem in the introduction.
• Begin by briefly re-stating the research problem you were investigating and answer all of the research questions underpinning the problem that you posed in the introduction.
• Describe the patterns, principles, and relationships shown by each major findings and place them in proper perspective. The sequencing of providing this information is important; first state the answer, then the relevant results, then cite the work of others. If appropriate, refer the reader to a figure or table to help enhance the interpretation of the data. The order of interpreting each major finding should be in the same order as they were described in your results section.
• A good discussion section includes analysis of any unexpected findings. This paragraph should begin with a description of the unexpected finding, followed by a brief interpretation as to why you believe it appeared and, if necessary, its possible significance in relation to the overall study. If more than one unexpected finding emerged during the study, describe each them in the order they appeared as you gathered the data.
• Before concluding the discussion, identify potential limitations and weaknesses. Comment on their relative importance in relation to your overall interpretation of the results and, if necessary, note how they may affect the validity of the findings. Avoid using an apologetic tone; however, be honest and self-critical.
• The discussion section should end with a concise summary of the principal implications of the findings regardless of statistical significance. Give a brief explanation about why you believe the findings and conclusions of your study are important and how they support broader knowledge or understanding of the research problem. This can be followed by any recommendations for further research. However, do not offer recommendations which could have been easily addressed within the study. This demonstrates to the reader you have inadequately examined and interpreted the data.

IV.  Overall Objectives

The objectives of your discussion section should include the following: I.  Reiterate the Research Problem/State the Major Findings

Briefly reiterate for your readers the research problem or problems you are investigating and the methods you used to investigate them, then move quickly to describe the major findings of the study. You should write a direct, declarative, and succinct proclamation of the study results.

II.  Explain the Meaning of the Findings and Why They are Important

No one has thought as long and hard about your study as you have. Systematically explain the meaning of the findings and why you believe they are important. After reading the discussion section, you want the reader to think about the results [“why hadn’t I thought of that?”]. You don’t want to force the reader to go through the paper multiple times to figure out what it all means. Begin this part of the section by repeating what you consider to be your most important finding first.

III.  Relate the Findings to Similar Studies

No study is so novel or possesses such a restricted focus that it has absolutely no relation to other previously published research. The discussion section should relate your study findings to those of other studies, particularly if questions raised by previous studies served as the motivation for your study, the findings of other studies support your findings [which strengthens the importance of your study results], and/or they point out how your study differs from other similar studies. IV.  Consider Alternative Explanations of the Findings

It is important to remember that the purpose of research is to discover and not to prove . When writing the discussion section, you should carefully consider all possible explanations for the study results, rather than just those that fit your prior assumptions or biases.

V.  Acknowledge the Study’s Limitations

It is far better for you to identify and acknowledge your study’s limitations than to have them pointed out by your professor! Describe the generalizability of your results to other situations, if applicable to the method chosen, then describe in detail problems you encountered in the method(s) you used to gather information. Note any unanswered questions or issues your study did not address, and.... VI.  Make Suggestions for Further Research

Although your study may offer important insights about the research problem, other questions related to the problem likely remain unanswered. Moreover, some unanswered questions may have become more focused because of your study. You should make suggestions for further research in the discussion section.

NOTE: Besides the literature review section, the preponderance of references to sources in your research paper are usually found in the discussion section . A few historical references may be helpful for perspective but most of the references should be relatively recent and included to aid in the interpretation of your results and/or linked to similar studies. If a study that you cited disagrees with your findings, don't ignore it--clearly explain why the study's findings differ from yours.

V.  Problems to Avoid

• Do not waste entire sentences restating your results . Should you need to remind the reader of the finding to be discussed, use "bridge sentences" that relate the result to the interpretation. An example would be: “The lack of available housing to single women with children in rural areas of Texas suggests that...[then move to the interpretation of this finding].”
• Recommendations for further research can be included in either the discussion or conclusion of your paper but do not repeat your recommendations in the both sections.
• Do not introduce new results in the discussion. Be wary of mistaking the reiteration of a specific finding for an interpretation.
• Use of the first person is acceptable, but too much use of the first person may actually distract the reader from the main points.

Analyzing vs. Summarizing. Department of English Writing Guide. George Mason University; Discussion . The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. Department of Biology. Bates College; Hess, Dean R. How to Write an Effective Discussion. Respiratory Care 49 (October 2004); Kretchmer, Paul. Fourteen Steps to Writing to Writing an Effective Discussion Section . San Francisco Edit, 2003-2008; The Lab Report . University College Writing Centre. University of Toronto; Summary: Using it Wisely . The Writing Center. University of North Carolina; Schafer, Mickey S. Writing the Discussion . Writing in Psychology course syllabus. University of Florida; Yellin, Linda L. A Sociology Writer's Guide. Boston, MA: Allyn and Bacon, 2009.

Writing Tip

Don’t Overinterpret the Results!

Interpretation is a subjective exercise. Therefore, be careful that you do not read more into the findings than can be supported by the evidence you've gathered. Remember that the data are the data: nothing more, nothing less.

Another Writing Tip

Don't Write Two Results Sections!

One of the most common mistakes that you can make when discussing the results of your study is to present a superficial interpretation of the findings that more or less re-states the results section of your paper. Obviously, you must refer to your results when discussing them, but focus on the interpretion of those results, not just the data itself.

Azar, Beth. Discussing Your Findings.  American Psychological Association gradPSYCH Magazine (January 2006)

Yet Another Writing Tip

Avoid Unwarranted Speculation!

The discussion section should remain focused on the findings of your study. For example, if you studied the impact of foreign aid on increasing levels of education among the poor in Bangladesh, it's generally not appropriate to speculate about how your findings might apply to populations in other countries without drawing from existing studies to support your claim. If you feel compelled to speculate, be certain that you clearly identify your comments as speculation or as a suggestion for where further research is needed. Sometimes your professor will encourage you to expand the discussion in this way, while others don’t care what your opinion is beyond your efforts to interpret the data.

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• Last Updated: Jul 18, 2023 11:58 AM
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How to Write the Discussion Section of a Research Paper

The discussion section of a research paper analyzes and interprets the findings, provides context, compares them with previous studies, identifies limitations, and suggests future research directions.

Updated on September 15, 2023

Structure your discussion section right, and you’ll be cited more often while doing a greater service to the scientific community. So, what actually goes into the discussion section? And how do you write it?

The discussion section of your research paper is where you let the reader know how your study is positioned in the literature, what to take away from your paper, and how your work helps them. It can also include your conclusions and suggestions for future studies.

First, we’ll define all the parts of your discussion paper, and then look into how to write a strong, effective discussion section for your paper or manuscript.

Discussion section: what is it, what it does

The discussion section comes later in your paper, following the introduction, methods, and results. The discussion sets up your study’s conclusions. Its main goals are to present, interpret, and provide a context for your results.

What is it?

The discussion section provides an analysis and interpretation of the findings, compares them with previous studies, identifies limitations, and suggests future directions for research.

This section combines information from the preceding parts of your paper into a coherent story. By this point, the reader already knows why you did your study (introduction), how you did it (methods), and what happened (results). In the discussion, you’ll help the reader connect the ideas from these sections.

Why is it necessary?

The discussion provides context and interpretations for the results. It also answers the questions posed in the introduction. While the results section describes your findings, the discussion explains what they say. This is also where you can describe the impact or implications of your research.

Adds context for your results

Most research studies aim to answer a question, replicate a finding, or address limitations in the literature. These goals are first described in the introduction. However, in the discussion section, the author can refer back to them to explain how the study's objective was achieved. 

Shows what your results actually mean and real-world implications

The discussion can also describe the effect of your findings on research or practice. How are your results significant for readers, other researchers, or policymakers?

What to include in your discussion (in the correct order)

A complete and effective discussion section should at least touch on the points described below.

Summary of key findings

The discussion should begin with a brief factual summary of the results. Concisely overview the main results you obtained.

Begin with key findings with supporting evidence

Your results section described a list of findings, but what message do they send when you look at them all together?

Your findings were detailed in the results section, so there’s no need to repeat them here, but do provide at least a few highlights. This will help refresh the reader’s memory and help them focus on the big picture.

Read the first paragraph of the discussion section in this article (PDF) for an example of how to start this part of your paper. Notice how the authors break down their results and follow each description sentence with an explanation of why each finding is relevant. 

State clearly and concisely

Following a clear and direct writing style is especially important in the discussion section. After all, this is where you will make some of the most impactful points in your paper. While the results section often contains technical vocabulary, such as statistical terms, the discussion section lets you describe your findings more clearly. 

Interpretation of results

Once you’ve given your reader an overview of your results, you need to interpret those results. In other words, what do your results mean? Discuss the findings’ implications and significance in relation to your research question or hypothesis.

Analyze and interpret your findings

Look into your findings and explore what’s behind them or what may have caused them. If your introduction cited theories or studies that could explain your findings, use these sources as a basis to discuss your results.

For example, look at the second paragraph in the discussion section of this article on waggling honey bees. Here, the authors explore their results based on information from the literature.

Unexpected or contradictory results

Sometimes, your findings are not what you expect. Here’s where you describe this and try to find a reason for it. Could it be because of the method you used? Does it have something to do with the variables analyzed? Comparing your methods with those of other similar studies can help with this task.

Context and comparison with previous work

Refer to related studies to place your research in a larger context and the literature. Compare and contrast your findings with existing literature, highlighting similarities, differences, and/or contradictions.

How your work compares or contrasts with previous work

Studies with similar findings to yours can be cited to show the strength of your findings. Information from these studies can also be used to help explain your results. Differences between your findings and others in the literature can also be discussed here. 

How to divide this section into subsections

If you have more than one objective in your study or many key findings, you can dedicate a separate section to each of these. Here’s an example of this approach. You can see that the discussion section is divided into topics and even has a separate heading for each of them. 

Limitations

Many journals require you to include the limitations of your study in the discussion. Even if they don’t, there are good reasons to mention these in your paper.

Why limitations don’t have a negative connotation

A study’s limitations are points to be improved upon in future research. While some of these may be flaws in your method, many may be due to factors you couldn’t predict.

Examples include time constraints or small sample sizes. Pointing this out will help future researchers avoid or address these issues. This part of the discussion can also include any attempts you have made to reduce the impact of these limitations, as in this study .

How limitations add to a researcher's credibility

Pointing out the limitations of your study demonstrates transparency. It also shows that you know your methods well and can conduct a critical assessment of them.  

Implications and significance

The final paragraph of the discussion section should contain the take-home messages for your study. It can also cite the “strong points” of your study, to contrast with the limitations section.

Restate your hypothesis

Remind the reader what your hypothesis was before you conducted the study. 

How was it proven or disproven?

Identify your main findings and describe how they relate to your hypothesis.

How your results contribute to the literature

Were you able to answer your research question? Or address a gap in the literature?

Future implications of your research

Describe the impact that your results may have on the topic of study. Your results may show, for instance, that there are still limitations in the literature for future studies to address. There may be a need for studies that extend your findings in a specific way. You also may need additional research to corroborate your findings. 

Sample discussion section

This fictitious example covers all the aspects discussed above. Your actual discussion section will probably be much longer, but you can read this to get an idea of everything your discussion should cover.

Our results showed that the presence of cats in a household is associated with higher levels of perceived happiness by its human occupants. These findings support our hypothesis and demonstrate the association between pet ownership and well-being. 

The present findings align with those of Bao and Schreer (2016) and Hardie et al. (2023), who observed greater life satisfaction in pet owners relative to non-owners. Although the present study did not directly evaluate life satisfaction, this factor may explain the association between happiness and cat ownership observed in our sample.

Our findings must be interpreted in light of some limitations, such as the focus on cat ownership only rather than pets as a whole. This may limit the generalizability of our results.

Nevertheless, this study had several strengths. These include its strict exclusion criteria and use of a standardized assessment instrument to investigate the relationships between pets and owners. These attributes bolster the accuracy of our results and reduce the influence of confounding factors, increasing the strength of our conclusions. Future studies may examine the factors that mediate the association between pet ownership and happiness to better comprehend this phenomenon.

This brief discussion begins with a quick summary of the results and hypothesis. The next paragraph cites previous research and compares its findings to those of this study. Information from previous studies is also used to help interpret the findings. After discussing the results of the study, some limitations are pointed out. The paper also explains why these limitations may influence the interpretation of results. Then, final conclusions are drawn based on the study, and directions for future research are suggested.

How to make your discussion flow naturally

If you find writing in scientific English challenging, the discussion and conclusions are often the hardest parts of the paper to write. That’s because you’re not just listing up studies, methods, and outcomes. You’re actually expressing your thoughts and interpretations in words.

• How formal should it be?
• What words should you use, or not use?
• How do you meet strict word limits, or make it longer and more informative?

Always give it your best, but sometimes a helping hand can, well, help. Getting a professional edit can help clarify your work’s importance while improving the English used to explain it. When readers know the value of your work, they’ll cite it. We’ll assign your study to an expert editor knowledgeable in your area of research. Their work will clarify your discussion, helping it to tell your story. Find out more about AJE Editing.

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Discussion section of a research paper

When writing a research paper, this is one of the most important part of a research paper.

The discussion section of a research paper is where you interpret the data and present your conclusions. In this section, you should discuss how your results relate to the hypotheses you proposed and what they mean for future research. You should also point out any limitations of your study and suggest ways that the findings could be further developed. Finally, you should briefly summarize the main points of your paper.

In many research papers, the discussion and conclusion sections usually overlap. However, it is still important to keep them separate so that your paper is organized and easy to follow.

What is an appendix in a paper?

Research paper conclusion, how to write preface for project report.

• Research paper introduction paragraph

Exploratory data analysis research paper

• Research Analysis Paper: How to Analyze a Research Article

What is the discussion section of a research paper?

The discussion section of a research paper is the section where the author discusses the findings of the study and how they relate to the existing body of knowledge on the topic.

The purpose of the discussion section is to interpret the findings of your study, and to explain how they relate to the existing body of scientific knowledge. This is a critical part of any research paper, as it helps to illustrate the significance of your work, and how it may impact future research. Additionally, the discussion section can highlight potential limitations of your study, and offer suggestions for future research.

When writing the discussion section of a research paper, it is important to keep the following in mind:

• The discussion section should be concise and focus on the key points of your study.
• Be sure to interpret your findings in light of the existing body of knowledge.
• Offer suggestions for future research.
• Discuss the potential limitations of your study.
• Remain objective and unbiased in your discussion.
• Use clear and concise language.
• Make sure your arguments are logically sound.
• Cite your sources appropriately.

How to write the discussion section of a research paper

Writing a discussion part of any research paper is not easy. It is the place where you need to show your understanding of the subject and present your arguments. The following tips will help you write a strong discussion section:

Summarize your key findings:

Start the discussion section by summarizing your main findings in a few sentences. This will help remind the reader of what you found and how it relates to your argument.

Evaluate your findings:

After you’ve summarize your findings, it’s important to evaluate how strong they are. Were your results significant? Do they support your argument? Are there any potential problems with your data or methods? These are the types of questions you should answer in this section.

Contextualize your findings:

After you’ve evaluated your findings, it’s important to put them in context. What do your results mean? How do they compare to what other scholars have found? How does your research contribute to the existing conversation on this topic? These are the types of questions you should answer in this section. Give your interpretation of what the findings mean. What do they suggest about the subject? Are there any implications for future research? Keep your writing clear and concise. Avoid over-explaining or going into too much detail. The goal is to help the reader understand your findings, not to teach them about the subject.

Show how your findings fit with what is already known about the topic. If there are differences, explain why they may exist.

Implications of your findings:

Finally, you’ll want to discuss the implications of your findings. What do they mean for your argument? For future research on this topic? For the world more broadly? What are the implications of your findings? What questions still need to be answered? These are the types of questions you should answer in this section.

Acknowledge the limitations:

Every study has limitations. Be honest about the limitations of your study and highlight any areas that need further research. Be critical and acknowledge the limitations of your study and highlight any areas that need further research. suggest ways in which future research could build on your findings.

In a research paper, limitations are usually found in the methodology section. However, it is also important to mention them in the discussion section as well. By acknowledging the limitations of your study, you show that you are aware of the potential for error and that you took steps to minimize it. This makes your research more credible.

To help illustrate the points made in this section, let’s look at a few examples.

Example 1: In a study on the effects of climate change on plant growth, the authors found that plants grown in warmer temperatures produced less biomass.

The results of this study suggest that climate change may have a negative effect on plant growth. However, there are some limitations to this study. First, the study was conducted in a controlled environment, so it is not clear if the results would be the same in the wild. Second, the study only looked at one aspect of plant growth (biomass production), so it is not clear if other aspects of plant growth would be affected by climate change. Third, the study did not take into account the effects of precipitation, which is also likely to play a role in plant growth.

Despite these limitations, the results of this study provide valuable insight into the potential effects of climate change on plant growth.

Example 2: In a study on the effectiveness of a new reading program, the authors found that students who used the program improved their reading scores.

The results of this study suggest that the reading program is effective. However, there are some limitations to this study. First, the sample size was small, so it is possible that the results are not representative of the population as a whole. Second, the study only looked at one measure of reading achievement (scores on a standardized test), so it is not clear if the program would have the same effect on other measures of reading achievement. Third, the study did not compare the students who used the program to a control group, so it is not clear if the improvement in reading scores was due to the program or to natural variation.

Despite these limitations, the results of this study provide valuable insight into the potential effectiveness of the reading program.

State your recommendations:

If appropriate, make recommendations for future research or practice. Recommendations could be based on your findings or on the limitations of your study.

Use the phrases to make recommendations:

• This study suggests that…
• Future research should…
• Further studies are needed to…
• This study has limitations that future research could address.
• The findings of this study have implications for…
• These findings suggest that policy makers should…

End with a strong conclusion:

End the discussion section with a brief conclusion that summarizes your findings and their significance. What are the implications of your findings? What questions still need to be answered? Leave the reader with a clear understanding of what you found and why it matters.

Your discussion section should be a critical evaluation of your findings, not just a summary. Remember to be clear, concise, and professional.

What to avoid in research paper discussion section

Here are 3 key items that you should avoid including when writing the discussion section of your research paper:

• Do not introduce new data or results : The discussion section is not the place to introduce new data.
• Avoid overstating your case : it is important to be honest and objective in your interpretation of the data. Do not try to force the data to fit your argument; instead, be willing to accept that it may not support your case.
• Avoid undermining your research : Be confident in your findings and avoid making statements that could undermine your study. For example, avoid phrases such as “this may not be generalizable” or “more research is needed.” These statements make it sound like you are unsure of your results.

What goes in the discussion section of a research paper?

The discussion section of a research paper is where you analyze your findings and interpret them. This section should be a critical evaluation of your findings, not just a summary. Remember to be clear, concise, and professional.

In the discussion section, you should:

• Introduce your findings and state the purpose of the study
• Discuss the results of the study
• Interpret the results of the study
• Discuss the limitations of the study
• Make recommendations for future research or practice
• Summarize your findings and their significance

Discussion section of a research paper example

Discussion template for research paper

The discussion section of a research paper includes 3 parts: an introductory paragraph, intermediate paragraphs and a conclusion paragraph . The introductory paragraph should provide a brief overview of the previous research that has been conducted on the topic. The intermediate paragraphs should present the findings of your study and how they compare or contrast with the findings of previous studies. The conclusion paragraph should summarize the main points of the discussion section and suggest possible future directions for research.

1. Start with a strong introduction. 2. Present your findings in a clear and concise manner. 3. Analyze your findings and offer your interpretation. 4. Summarize your discussion and offer concluding thoughts.

The discussion section is where you analyze your results and put them into context. You should discuss how your results compare to other studies, what they mean for the field of research, and how they can be applied to real-world problems. You should also highlight any weaknesses or limitations of your study so that future researchers can build on your work. Finally, you should suggest future directions for research based on your findings.

A discussion in research is section where the author discusses the results of the study and how it can be improved.

Author: tutlance

• Hook for research paper

research paper title page

Parts of a research paper.

• How to write the methods section of a research paper

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APA Sample Paper

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101+ Unique Discussion Essay Topics, Questions and Ideas

In an academic setting, the meaning of a discussion is similar to its day-to-day use, i.e., two or more people talking about a particular subject with differing perspectives. However, in the case of a discussion essay, a balanced view and presentation of ideas and opinions are advisable. It aims to test for your writing, learning, critical analysis and researching skills.

A discussion essay is a task that aims to test your ability to present and deliberate upon issues surrounding a certain debatable topic. You will be expected to present both sides of the discussion while still presenting your position on the same. Therefore, you have to ensure you have access to appropriate and up to date research material.

Discussion assignments are among the most common tasks offered to college students and can be based on various disciplines, and the concepts learnt in class. When presented with such an assignment it is totally understandable that you feel overwhelmed with the workload. However, you should take your time to deliver a high-quality discussion essay that meets all the requirements presented by your teacher. You should start with:

• Select an appropriate discussion title;
• Choose a side;
• Conduct research on the topic;
• Outline and structure the elements of your document;
• Come up with your thesis statement;
• Start writing your essay (introduction, body, and conclusion).

How to Select the Best Discussion Essay Topic? An Informative and Detailed Guide

This guide will focus on helping you select an appropriate essay title for your discussion assignment. Once you have been given a discussion essay assignment, start by reading the instruction to understand what is expected of you. The next step would be to deliberate on which topics and ideas would best fit the requirements of the essay.

Narrow down your thoughts to a few subjects that you are comfortable with and choose one topic that suits the assignment.  A good essay must contain a valid analysis and fair criticism of the subject; thus, the title you select must be debatable. That is, it must be logical and supported by factual information and substantial evidence.

It takes some time and effort to identify the right title to fulfill your assignment. Above all the topic should be relevant and informative to the reader. Here are characteristics of a suitable discussion essay topic that you should look for:

• Covers a specific subject;
• Clear and well-defined;
• Has significant importance;
• Interesting and relatable;
• Should be unique and original.

List of Discussion Essay Topics to Use within Your Assignment

You might think that it is better when you are assigned a specific essay title to write about. Yes, it is understandable why you would think that; however, many students claim that it is better to have the opportunity to select your discussion essay topic. Below are 50 common examples of discussion topics for your paper:

• Effect of greenhouse gasses on the environment
• The cause and impact of obesity on US citizens
• The impact of civil wars on women and children
• Social implications of continued social media dependency
• Online computer game addiction
• A comparison of the adverse effects of both natural calamities
• Contraceptives and their impact on teenage pregnancies
• The integration of music and dance into the school curricula
• Impact of excessive marijuana use by the youth
• The complexity of the American systems of learning
• The impact of Internet connectivity on modern education systems
• Advantages and disadvantages of learning a secondary language
• Pros and cons of international student exchange programs in the US
• Advantages and disadvantages of concealed carry firearm regulation in the US
• The negative effects of anorexia on pregnant women
• The positive and negative impact on the Vietnam war on the American economy
• The significance of Richard Nixon’s role in the Watergate scandal
• The negative effects of gun violence in US high schools
• The challenges faced by environmental conservationists
• The positive and negative influence of advertisements on customer tastes and preferences
• Prolonged drug use – a medical condition or a crime
• Global climate change as a result of human behavior
• The introduction of sporting activities in schools
• The benefits and drawbacks of the storage and distribution of personal information by social media companies
• Positive and negative effects of cloning and gene editing technologies
• Drawbacks of human and wild animal interaction
• The influence of social media on people’s social interaction
• The importance of artificial intelligence in the health sector
• The use of technology in war and how it has influenced modern warfare
• The widespread use of social media by cyber terrorists
• The pros and cons of the industrial revolution in people’s jobs
• Benefits and drawbacks of government control on the use of technology
• Benefits and risks of nuclear power production
• Advantages and disadvantages of post graduate programs in developing nations
• Positive and negative implications of a free education
• The underutilization and wastage of taxpayer’s resources
• The trade war and its negative effect on the global economy
• The great recession, its causes, and effects on the American economy
• E-commerce and how it is changing the way people conduct business
• A detailed comparison of capitalism and socialism
• Measures to reduce unemployment in African countries
• Advantages and disadvantages of forming trade unions
• Importance of technology in the delivery of goods and services worldwide
• Significant Differences between bilateral and multilateral trade
• The health risks associated with the distribution of cigarettes worldwide
• Advantages and disadvantages of globalization
• Social media and its contribution to business
• Benefits and drawbacks of having an export-based economy
• Pros and cons of first world countries helping the poor in third world nations
• The positive and negative implications of the use of CCTV cameras on user privacy

Discussion Topics About Society

Below are a few more discussion essay titles on the subject of family and society that could interest you:

• The positive and negative impact of the ‘me-too’ movement on the society
• Gender equality pros and cons of international business relations
• The simplicity or complexity the process LGBT families follow to adopt children
• Positive and negative ethical considerations of the prostitution legalization
• The benefits and drawbacks of distribution of contraceptives in schools
• The portrayal of violence and sexual behavior online
• Advantages and disadvantages of maternity leave for both parents
• Advantages and disadvantages of the death penalty
• The contribution of the church in the society
• The positive and negative effects of an increase in the school workload
• Juvenile detention centers and the positive and negative impact on offenders
• The rehabilitation processes in US maximum security prisons
• Corporal punishment and why it is still in use in some African countries
• The pro and cons of homeschooling today
• The physiological effect a foster home has on children
• Abortion and the adverse effects on the mother
• The safety in public and private learning institutions
• Chinese government support of birth control technologies
• Advantages and disadvantages of the family decision being left solely to men
• Lessons about sex education and at what age should they be offered
• The positive and undesirable results of family relations
• Noticeable differences in the various branches of Christianity
• School uniforms and why they should be a necessary part of the US education system
• The negative effects of pornography on the youth
• Positive and negative outcomes of abortion

Discussion Topics on Politics

Below are some unique essay topics on various up to date political subjects that you should definitely take into consideration:

• The increase in gun violence in the US
• The role of the North Atlantic Treaty Organization
• Industrialization and global trade in China
• Illegal immigration into the US via the Mexican border
• The purpose of tax-payers to the development of their nations
• United States citizenship laws and how they have contributed to its growth
• Extradition laws for convicted criminals in the US
• The prospect of the first US female president
• The positive and negative impact of conspiracy in a political environment
• The effectiveness of international trade laws
• The similarities of the American and French revolutions
• Similarities that exist between infamous dictators and school bullies
• Pros and cons of Russia’s interference with the United States electoral process
• Positive and negative implications on the exit of the United States from the Paris Agreement on climate change
• A comparison of the leadership styles of the US and North Korean presidents
• The American presidency and why it is a global symbol of power
• Advantages and disadvantages of the north Korean nuclear disarmament program
• Positive and negative implications of the appointment of supreme court judges in the US
• The likely triggers for a third world war

Sports Discussion Topics

Common discussion essay tittles used in sports:

• The adverse effect of doping in sports
• The negative impact of corruption within sports governing bodies
• The prevalence of soccer over American football worldwide
• Hunting as a sport and why it should be controlled
• The adoption of successful sports personalities from developing nations
• Advantages and disadvantages of the interaction among people with different religious beliefs
• How has technology improved sports worldwide
• The political nature of major sporting events
• The benefits of using technology to identify cheats
• Popular games enjoyed worldwide that are dangerous
• Video refereeing as a game changer on sports
• The development of sports activities
• The effect of early childhood fame on their adult lives

Popular List of Discussion Essay Questions for your Assignments

Below is a list of discussion questions you should have a look at before you start your assignment:

• What are the adverse effects of cyber terrorism?
• What is the difference between privacy and confidentiality concerning internet usage?
• How does parental censorship help prevent children from accessing unwanted or harmful content on the internet?
• Is gaming affecting the mental health of children?
• Is there a need to add even more restrictions on Internet content in schools?
• What is the impact of Internet use on a person’s level of creativity?
• How does the Internet contribute to making the world a digital village?
• Discuss the benefits and shortfalls of using mobile phones in class for student
• Is digitalization a threat to the human workforce?
• Will the continued development of AI platforms render human labor irrelevant?

Unique Discussion Essay Ideas to Pick for Your Assignment

Below are 6 unique discussion ideas for your essays:

• No one owns the internet. According to the statement, you can discuss the benefits and challenges associated with the implementation of security features over the internet.
• Both online and offline gaming is a multimillion-dollar industry. You can write about how the psychological risk of online gaming is overshadowed by the financial benefits to be had.
• Technology is rapidly changing; every so often new and more advanced devices are developed making previous models obsolete. You can write about the negative impact of e-waste and how it can be properly disposed of.
• The slow development of most third world countries is often attributed to a lack of quality education. Write about the positive and negative impact of education on a nation’s development.
• When it comes to the idea of socialization, write about the pros and cons of using social media to beat the idea of loneliness.
• Online shopping has in recent years gained overwhelming popularity. Discuss the advantages and disadvantages of online shopping.

What You Could Do If Struggle Finishing Assignments

By using the list that we have compiled for you, you will have a variety of topics and ideas to choose from. However, you may also be stuck and don’t know where to start or how to format your paper. If for any reason you are unable to do your assignment within the provided deadline you can request for a deadline extension from your instructor.

Alternatively, you can seek professional assistance from a qualified writer. At our company, we have competent and expert writers to help write the assignment for you. Do not hesitate to contact our customer support team for any guidance or inquiry about writing your paper. Place an order with our world-class writers, and we will deliver your assignment before the deadline. Order now and you will be happy.

• Open access
• Published: 18 October 2023

Elucidating regulatory processes of intense physical activity by multi-omics analysis

• Ernesto S. Nakayasu   ORCID: orcid.org/0000-0002-4056-2695 1 ,
• Marina A. Gritsenko 1 ,
• Young-Mo Kim 1 ,
• Jennifer E. Kyle 1 ,
• Kelly G. Stratton 1 ,
• Carrie D. Nicora 1 ,
• Nathalie Munoz 2 ,
• Kathleen M. Navarro 3 ,
• Daniel Claborne 4 ,
• Yuqian Gao 1 ,
• Karl K. Weitz 1 ,
• Vanessa L. Paurus 1 ,
• Kent J. Bloodsworth 1 ,
• Kelsey A. Allen 5 ,
• Lisa M. Bramer 1 ,
• Fernando Montes 6 ,
• Kathleen A. Clark 7 ,
• Grant Tietje 5 ,
• Justin Teeguarden 2 , 8 &
• Kristin E. Burnum-Johnson 2  

Military Medical Research volume  10 , Article number:  48 ( 2023 ) Cite this article

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Physiological and biochemical processes across tissues of the body are regulated in response to the high demands of intense physical activity in several occupations, such as firefighting, law enforcement, military, and sports. A better understanding of such processes can ultimately help improve human performance and prevent illnesses in the work environment.

To study regulatory processes in intense physical activity simulating real-life conditions, we performed a multi-omics analysis of three biofluids (blood plasma, urine, and saliva) collected from 11 wildland firefighters before and after a 45 min, intense exercise regimen. Omics profiles post- versus pre-exercise were compared by Student’s t -test followed by pathway analysis and comparison between the different omics modalities.

Our multi-omics analysis identified and quantified 3835 proteins, 730 lipids and 182 metabolites combining the 3 different types of samples. The blood plasma analysis revealed signatures of tissue damage and acute repair response accompanied by enhanced carbon metabolism to meet energy demands. The urine analysis showed a strong, concomitant regulation of 6 out of 8 identified proteins from the renin-angiotensin system supporting increased excretion of catabolites, reabsorption of nutrients and maintenance of fluid balance. In saliva, we observed a decrease in 3 pro-inflammatory cytokines and an increase in 8 antimicrobial peptides. A systematic literature review identified 6 papers that support an altered susceptibility to respiratory infection.

This study shows simultaneous regulatory signatures in biofluids indicative of homeostatic maintenance during intense physical activity with possible effects on increased infection susceptibility, suggesting that caution against respiratory diseases could benefit workers on highly physical demanding jobs.

Physical activity induces a multi-organ response to increased energy needs, oxygen demands, and the consequences of tissue damage [ 1 ]. Demands that exceed adaptive capacity, can overcome these homeostatic mechanisms, leading to exhaustion, decreased human performance, and increased worker susceptibility to injury or disease [ 2 , 3 , 4 ]. Improving our understanding of these synchronized regulatory processes would enable us to monitor the balance between adaptive and adverse responses to intense physical exercise to predict the early stages of exhaustion, develop interventions that improve performance and recovery, and mitigate health risks for occupations involving intense physical activity, such as firefighting, law enforcement, military, and sports.

Mass spectrometry-based multi-omics analysis of biological fluids, such as blood plasma, saliva, and urine, is one of the most promising approaches for studying the dynamics of the molecular regulation of normal, adaptive, and disease states in humans. Continual advances in instrumentation have enabled the identification and quantitation of thousands of biomolecules per sample, leading to comprehensive views of the regulated processes [ 5 , 6 , 7 , 8 , 9 , 10 ]. A pioneer metabolomics study reported that glycogenolysis, the tricarboxylic acid (TCA) cycle and lipolysis were major activated processes in acute and prolonged aerobic exercises [ 11 ]. Contrepois et al. [ 5 ] performed a multi-omics analysis of plasma and leukocytes from human volunteers that underwent an acute aerobic exercise session that revealed a highly orchestrated landscape of molecular signals and processes that support human physical activity. Omics analysis has also shown memory improvement due to exercise-mediated anti-inflammatory effects [ 12 ]. A meta-omics analysis of elite marathon runners found that the gut bacterium Veillonella atypica ( V. atypica ) was associated with increased performance [ 13 ]. Additionally, the administration of V. atypica to mice improved their performance, which was attributed to the conversion of lactate produced in the muscle into propionate at the intestinal surface [ 13 ]. In another example, injection of glycosylphosphatidylinositol-specific phospholipase D1 into sedentary mice was shown to recapitulate the cognitive benefits induced by exercise [ 14 ]. These findings represent a proof of concept that physical performance can be improved with exogenous treatments based on an understanding of the underlying physiological processes and their molecular transducers.

A fundamental question in exercise physiology is how different tissues of the body are regulated to meet the physiological and metabolic demands of intense exercise while simultaneously maintaining homeostasis. Here, we investigated the molecular regulatory signatures of strenuous exercise by performing proteomics, lipidomics and metabolomics analyses of wildland firefighters following an intense 45 min exercise session at the aerobic threshold. We chose to study wildland firefighters due to their arduous work under difficult conditions in remote locations for shifts often longer than 24 h, and for up to 14–21 days. During the peak of the 2020 wildfire season (September 2020), over 32,000 wildland fire personnel were deployed across the Western United States to participate in fire suppression [ 15 ]. Our data shows strong signatures of molecular regulation in the different biofluids, providing insights into the molecular coordination between tissues during intense physical activity. We also performed a systematic literature review to investigate the potential health consequences of the molecular regulation in response to extreme physical activity and training. This is an important step towards building the capability to monitor the balance between adaptive and adverse responses and to predict the early biochemical and physiological stages of exhaustion, in pursuit of reducing the occupational risk of firefighters, first responders and other high-stress occupations.

Study design, sample cohort and randomization

Sample size calculations were performed to determine the necessary number of subjects assuming an experimental design with data collection before and after exercise. As is standard, a type 1 error rate of 0.05 and a power of 0.80 were assumed, and the median standard deviation, was used to estimate typical variability in the data. Power analyses were conducted based on an ongoing study’s lipidomics dataset, showing that 5 samples would be needed for a 0.8 power to reach statistical significance with ≥ 1.5-fold change in 75% of the measured molecules. A total of 13 male firefighter volunteers with the average age of (25 ± 3) years old and average body mass index of (26.3 ± 3.3) kg/m 2 before exercise were recruited. All volunteers that agreed to participate were included, without exclusion criteria, to have a better representation of the firefighter population.

The volunteers underwent an exercise session that consisted of hiking outdoors over hilly terrain in Santa Clarita, CA, with full wildland firefighter gear that weighed from 9 to 20 kg. Volunteers’ blood was collected pre- and post-exercise by phlebotomy and immediately placed on ice. The post-sample was collected within 10 min after the exercise. Blood was drawn by professional phlebotomists from different arms for baseline and after exercise sampling to avoid local responses related to the drawing process. The skin surface was wiped with antiseptic tissue before the puncture to minimize contamination. Blood was drawn into one 6 ml ethylenediaminetetraacetic acid (EDTA)-coated vacuum tube (Vacuntainer, BD, Franklin Lakes, NJ, USA), mixed by inverting the tube 8–10 and immediately placed on ice. Plasma was then separated by centrifugation at 1000× g for 10 min at room temperature. Collected plasma was visually inspected for coagulation and hemolysis, collected into 0.5 ml aliquots, and stored within 1 h of blood draw. For the saliva collection, volunteers rinsed their mouths 3 times for 30 s each with water and then dripped the saliva directly into the tube without spitting to avoid contamination with other fluids of the respiratory and gastroesophageal systems and placed on ice. Urine was collected by directly urinating into tubes and placed on ice. Immediately after collection, plasma, saliva, and urine samples were stored at − 80 °C. Sample collection, preparation and instrument run orders were randomized to minimize confounding factors.

Ethics approval and consent to participate

The study was conducted after approval from the Institutional Review Board of the Pacific Northwest National Laboratory (PNNL IRB #2019-17) and participants signed information consent in accordance with federal regulations. The consent signed by participants of the study included permission for publishing the research findings and was captured in accordance with federal regulations.

Sample preparation for multi-omics analysis

Simultaneous metabolite, protein and lipid extraction (mplex).

Biofluids were transferred into 2 ml Sorenson MµlTI™ SafeSeal™ tubes (Sorenson BioScience, Inc., Salt Lake City, UT, USA) with gas chromatography-mass spectrometry (GC-MS) heavy isotope internal standard mix, GC-IS (1 mg/ml in water each 2 H 4 -malonic acid, 2 H 4 -succinic acid, 2 H 5 -glycine, 2 H 4 -citric acid, 13 C 6 -fructose, 2 H 5 -tryptophan, 2 H 4 -lysine, 2 H 7 -alanine, 2 H 35 -stearic acid, 2 H 5 -benzoic acid, 2 H 15 -octanoic acid): plasma − 1:1 (v:v, sample: GC-IS), urine− 4:1 (v:v, sample: GC-IS). Urine was further treated with 1 mg/ml urease at 37 °C with mild shaking (500 rpm) for 30 min and incubated on ice for 1 min. Plasma sample was also spiked with 10 μl SPLASH mix (in methanol) (Avanti Polar, Alabaster, AL, USA). Extraction was perfumed using the MPLEx protocol [ 16 ] . A 2:1 (v:v) chloroform/methanol mix was added to the samples to make a ratio of 8:4:3 (v:v:v) chloroform/methanol/water. Samples were then vortexed and incubated on an ice block for 5 min. The layers were separated by centrifugation at 12,000× g for 10 min at 4 °C. For plasma samples, 66.7 µl (from a total 500 µl extraction volume) of the lower lipid layer was transferred to a glass autosampler vial and dried in a centrifugal vacuum concentrator. The upper liquid layer and the rest of the bottom layer were transferred to another autosampler vial for metabolites and dried. For the other biofluids, the upper and lower phases were collected into separate files. The dried metabolites were capped and stored at − 20 °C for metabolomics analysis. The dried lipids had 500 µl 2:1 chloroform: methanol added, capped, and stored for lipidomics analysis. The protein pellet was washed with 1 ml of ice-cold methanol and centrifuged to the pellet, supernatant was removed and allowed to dry in a fume hood. Proteins were dissolved in 8 mol/L urea prepared in 50 mmol/L Tris-HCl, pH 8.0 and concentration was measured by BCA Protein Assay (Thermo Scientific, San Jose, CA, USA). Disulfide bonds were reduced for 1 h at 37 °C with 5 mmol/L dithiothreitol (Sigma-Aldrich, St. Louis, MO, USA) from a 500 mmol/L stock solution. Reduced cysteine residues were alkylated by adding 500 mmol/L iodoacetamide (Sigma-Aldrich, St. Louis, MO, USA) to a final concentration of 10 mmol/L and incubating in the dark at 25 °C for 45 min. Samples were diluted fourfold with 50 mmol/L Tris-HCl, pH 8.0 and digested with lysyl-C endopeptidase (FUJIFILM Wako Chemicals, Richmond, VA, USA) at 1:50 enzyme‐to‐substrate ratio at 25 °C for 2 h. The same amount of sequencing-grade modified trypsin (Promega, Madison, WI, USA) was added to the samples for 14 h incubation at 25 °C. The reaction was stopped by acidifying the samples with 100% formic acid (Sigma-Aldrich, St. Louis, MO, USA) to a final concentration of 1% formic acid, extracted in C18 SepPak cartridges (Waters, Milford, MA, USA) and dried in a centrifugal vacuum concentrator (Thermo Fisher Scientific, Carlsbad, CA, USA).

Metabolite extraction with methanol

Metabolites were also extracted with methanol for more comprehensive coverage. Plasma and urine samples were spiked with GC-IS as described above. Urine was also treated with urease. Eight volumes of ice-cold methanol were added, and samples were vortexed for 10 s and placed in ice blocks for 10 min and vortexed for 3 min. Centrifuged at 15,000× g at 4 °C for 10 min and the supernatant was transferred to autosampler vials and dried in a centrifugal vacuum concentrator. Dried metabolites were capped and stored at − 20 °C for further metabolomics analysis.

Plasma sample preparation for isobaric labeled proteomic analysis

Plasma abundant proteins were depleted using a Multiple Affinity Removal System (MARS) column (Hu-14 4.6 × 100 mm, Agilent Technologies, Santa Clara, CA, USA) coupled with a 1200 series HPLC (Agilent Technologies, Santa Clara, CA, USA). A total of 40 μl of plasma was diluted eightfold with Agilent buffer A and filtered with a 0.22 µm centrifugal filter. Samples were loaded onto MARS column for 27 min LC gradient (18 min sample load at 0.125 ml/min, then washed for 2 min at 1 ml/min with Agilent buffer A, and high abundant proteins eluted for 7 min at 1 ml/min Agilent buffer B). Unbound fractions, containing low- and mid-abundant proteins from the same participant were pooled, then concentrated and had their buffer exchanged to 50 mmol/L Tris-HCl, pH 8.0 using 3-kD molecular mass cutoff Amicon centrifugal filters (Millipore, Burlington, MA, USA) following the manufacturer’s instructions. Proteins were digested as described above and labeled with 11-plex tandem mass tags (TMT, Thermo Fisher Scientific Carlsbad, CA, USA) according to the manufacturer’s recommendations. One of the TMT channels was loaded with a pooled peptide mixture from all the samples, which serves as a reference to normalize across different sets of samples. Labeled peptides were fractionated into 96 fractions by high pH reversed-phase chromatography and concatenated into 24 fractions, as previously described [ 17 , 18 ].

Proteomics analysis

Peptides were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using a nanoAquity UPLC ® system (Waters Corporation, Milford, MA, USA) connected to a Q-Exactive mass spectrometer (Thermo Scientific, San Jose, CA, USA) as described in detail elsewhere [ 19 ]. Data from the TMT-labeled experiment were processed with Decon2LS software combined with DTA Refinery (version 2, Pacific Northwest National Laboratory, Richland, WA, USA) [ 20 , 21 ] for mass recalibration and peak list extraction. Peptides were identified with MSGF+ [ 22 ] by searching against the human version of the SwissProt database downloaded from Uniprot Knowledgebase on February 22, 2019. The searching parameters consisted of 1) parent ion mass tolerance of ± 6 ppm, 2) tryptic digestion in at least one of the termini with 2 missed cleavages allowed, 3) cysteine carbamidomethylation (+ 57.0215 Da) and N -terminal/lysine TMT labeling (+ 229.1629 Da) derivatization as static modifications, and 4) following variable modifications: oxidation (+ 15.9949 Da) on methionine, cysteine, tyrosine and tryptophan; dioxidation (+ 31.9898 Da) on cysteine; and deamidation/deamination (+ 0.98402 Da) on asparagine, glutamine and arginine residues. Data were filtered at spectral-peptide match (MSGF probability ≤ 1 × 10 −9 ), peptide (MSGF probability ≤ 7 × 10 −11 ) and protein (MSGF probability ≤ 2 × 10 −12 ) levels, resulting in < 1% false-discovery rate in each of the levels. TMT reporter ion intensities were extracted with MASIC [ 23 ] (version 1, Pacific Northwest National Laboratory, Richland, WA, USA), and the intensities of multiple MS/MS spectra from the same peptide were summed together to remove redundancy.

Label-free proteomics data were processed with MaxQuant (version 1.6.5.0, Max Planck Institute, Planegg, Germany) [ 24 ] by searching tandem mass spectra against the human proteome database downloaded from Uniprot Knowledgebase ( https://www.uniprot.org/ ) on September 23, 2019. Searching parameters considered trypsin cleavage in both peptide termini, methionine oxidation and protein N-terminal acetylation as variable modifications and cysteine carbamidomethylation as fixed modification. Mass tolerance of parentions was set to 20 and 4.5 ppm for prior and after mass recalibration, respectively. The remaining parameters were set as the software default options. Resulting identifications were filtered with a ≤ 1% false-discovery rate in both peptide-spectrum match and protein levels. Label-free quantification and intensity-based absolute quantification methods were used for the MaxQuant analysis. For this analysis, the match between runs option was enabled to decrease missing values.

The saliva microbiome analysis was processed with Decon2LS software combined with mzRefinery (version 2, Pacific Northwest National Laboratory, Richland, WA, USA) [ 25 ] for mass recalibration and peak list extraction. Peptides were identified with MSGF + using the human SwissProt database combined with the Human Oral Microbiome Database (downloaded from https://www.homd.org/ on February 17, 2020). The searching parameters consisted of 1) parent ion mass tolerance of ± 20 ppm, 2) tryptic digestion of both termini with 2 missed cleavages allowed, 3) cysteine carbamidomethylation (+ 57.0215 Da) as invariable modification and 4) methionine oxidation (+ 15.9949 Da) as variable modification. Data were filtered at spectral-peptide match (MSGF probability ≤ 1.0 × 10 −9 ), peptide (MSGF probability ≤ 1 × 10 −11 ) and protein (MSGF probability ≤ 1 × 10 −12 ) levels, resulting in < 1% false-discovery rate in each of the levels. The results led to the identification of proteins from 142 bacterial genera. For the quantitative analysis, we appended the top strain of each of the 142 bacterial genera to the human SwissProt database (both downloaded from https://www.uniprot.org/ on April 5, 2020) and reanalyzed the data with MaxQuant v.1.6.14, which can identify and quantify proteins but performs better in smaller sequence databases [ 26 ]. The same parameters for the label-free proteomics analysis were used to process the data.

Metabolomic analysis

Metabolites were derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) (Sigma-Aldrich, Saint Louis, MO, USA) and trimethylchlorosilane (TMCS) (Sigma-Aldrich, Saint Louis, MO, USA) and analyzed on Agilent GC 7890A using a HP-5MS column (30 m × 0.25 mm × 0.25 μm; Agilent Technologies, Santa Clara, CA, USA) coupled with a single quadrupole MSD 5975C (Agilent Technologies, Santa Clara, CA, USA) as previously described [ 27 ]. Fatty acid methyl ester standard mix (C8-28) (Sigma-Aldrich, Saint Louis, MO, USA) was analyzed in parallel as standard for retention time calibration. Collected data were calibrated and deconvoluted using Metabolite Detector (version 2, Technical University, Braunschweig, Germany) [ 28 ]. Identification of molecules was done by matching against the FiehnLib library [ 29 ] with additional in-house entries and the NIST17/Wiley 11 GC-MS spectral databases.

Lipidomic analysis

Lipids were subjected to LC-MS/MS analysis on orbitrap mass spectrometry (Velos Orbitrap, Thermo Fisher Scientific, San Jose, CA, USA) as previously described [ 30 ]. Lipid species were identified using LIQUID (version 1, Pacific Northwest National Laboratory, Richland, WA, USA) [ 30 ] and identifications were manually validated based on the MS/MS spectra (diagnostic and corresponding acyl chain fragments), the precursor isotopic profile, extracted ion chromatogram, mass measurement accuracy and elution time. Quantification was performed with MZmine (version 2, VTT Technical Research Centre of Finland) [ 31 ]. All LC-MS/MS data were aligned and gap-filled to the identified lipid-based observed m/z and retention time. Aligned features were manually verified and peak apex intensity values were exported for statistical analysis.

Dermcidin ELISA assay

Dermcidin was quantified using an ELISA kit (catalog number MBS2704747, MyBioSource, San Diego, CA, USA). One-hundred microliters of plasma or saliva were plated onto 96-well plates and incubated for 1 h at 37 °C, then add Detection Reagent A and incubate for another hour at 37 °C. After this period, plates were washed 3 times with 350 μl of wash buffer before incubation with appropriate Detection Reagent B for 30 min at 37 °C. Plates were washed 5 times with 350 μl of wash buffer and incubated with 90 μl of Substrate Solution for 20 min at 4 °C. The reaction was quenched with 50 μl of Stop Solution and measured at 450 nm in a plate spectrophotometer.

Urea quantification assay

Urine urea concentration was determined with a urease-based kit (Sigma-Aldrich, Saint Louis, MO, USA) following manufacturer-provided protocol. Fifty microliters of reaction mix containing Urea assay buffer, Peroxidase substrate, Enzyme mix, Developer and Converting Enzyme, was mixed with 50 μl of 1500-fold diluted urine and incubated for 60 min at 37 °C. The reaction was measured at 570 nm in a plate spectrophotometer.

Systematic literature review

The literature search was done between February 26 and March 16, 2021, by querying PubMed for publications (see Table  1 for keywords). The groups of workers that were included in this search were firefighters, soldiers, marathon runners and soccer players. Only studies that followed up individuals for respiratory infections after physical activity were included in the analysis.

Statistical analysis

Statistical analyses were conducted in R version 3.6 using the pmartR [ 32 ] and stats packages. Missing values were converted to “NA” and data were Log 2 transformed. TMT-labeled proteomics data were normalized to the reference pool. Peptides shared by multiple proteins were excluded. Biomolecules appearing only once across all samples were excluded. A robust Mahalanobis distance based on peptide abundance vectors (rMd-PAV) was calculated to identify potential sample outliers in the data [ 33 ]. Sample outliers were confirmed using visual inspection of correlation heatmaps and principal component analysis (PCA) plots. The metabolomics and lipidomics datasets were normalized via global median centering. Proteomics datasets were normalized by the statistical procedure for the analyses of peptide abundance normalization strategies (SPANS) [ 34 ] at the peptide level, and rolled up with R-rollup. Statistical comparisons of biomolecule abundances were performed using a paired Student’s t -test and considered significant with a P -value ≤ 0.05 without further corrections.

Functional-enrichment analysis

Differentially abundant proteins (Student’s t -test P -value ≤ 0.05) were submitted for functional-enrichment analysis using DAVID (version 6.8, Frederick National Laboratory for Cancer Research, Frederick, MD, USA) [ 35 ] and the whole set of human predicted genes was used as the background. Only the pathways containing KEGG annotation were considered in the analysis. Graphs of pathways overrepresented with differentially abundant proteins were plotted with Minitab (version 19.2020.1, Minitab LLC, State College, PA, USA). Lipid ontology and enrichment analysis were done using Lipid Mini-On (version 1, Pacific Northwest National Laboratory, Richland, WA, USA) [ 36 ].

Blood plasma, urine, and saliva were collected from wildland firefighters before and after an exercise, which consisted of hiking for 45 min, at a strenuous pace, in hilly terrain, while wearing full wildland firefighter gear (between 9 and 20 kg). Exercise sessions occurred at the start of the fire season, in late June 2019, during onboard training. The local temperature was 20 °C, while the air humidity was 78% with 6 km/h winds. From the initial 13 male firefighters, two participants were excluded, one was unable to finish the exercise regimen and a second study participant exceeded the post-exercise biospecimen collection time threshold. Participants that concluded the course were on average (25 ± 3) years old and weighed on average (80.1 ± 13.5) kg before exercise, and lost, on average, (1.8 ± 0.2) kg (2.2% of the initial weight) during exercise. The participants’ body mass index reduced from (26.6 ± 3.3) kg/m 2 pre-exercise to (26.0 ± 3.3) kg/m 2 post-exercise. Each biofluid was submitted for comprehensive proteomics, lipidomics and metabolomics analyses. Combining all the analyses 3835 proteins, 730 lipids and 182 metabolites were identified and quantified (Additional file 1 : Tables S1–S3). The different omics measurements were then integrated to provide a global view of physiological and biochemical pathways regulated during the exercise session that is released into different biofluids.

Multi-omics signatures of intense exercise in plasma

The plasma proteomics analysis resulted in the identification and quantification of 1510 proteins. Out of the 1510 identified proteins, 142 significantly (Student’s t -test P  ≤ 0.05, 107 up-regulated and 35 down-regulated) changed across the pre- and post-exercise plasma samples (Additional file 1 : Table S4). The paired metabolomics analysis of the same samples led to the identification of 91 metabolites, 29 up-regulated and 35 down-regulated (Additional file 1 : Table S5). A lipidomics analysis resulted in the identification of 391 lipid species, 149 of which were up-regulated and 77 of which were down-regulated (Additional file 1 : Table S6). A functional-enrichment analysis of the proteomics data shows that pathways related to Staphylococcus aureus infection, systemic lupus erythematosus and prion diseases were down-regulated post-exercise (Fig.  1 a), possibly indicating immune modulation. Complement and coagulation cascades had proteins simultaneously down-regulated and up-regulated post-exercise, while the coagulation proteins were up-regulated, and the complement proteins were down-regulated (Fig.  1 a and Additional file 1 : Table S4). Enrichment of pathways such as ECM-receptor interaction, focal adhesion, and proteoglycans in cancer (Fig.  1 a) showed a general increase in extracellular matrix (ECM) proteins. Except for osteopontin, all the other 11 proteins of the ECM-receptor interaction pathway were up-regulated post-exercise (Fig.  1 b). As a loading control, the abundant plasma protein, ceruloplasmin, was unaffected by the exercise session (Fig.  1 b). The release of ECM proteins into the blood might be due to tissue damage.

Comparative multi-omics analysis of blood plasma prior and post exercise. a Functional-enrichment analysis of proteins differentially abundant (Student’s t -test P  ≤ 0.05) after the exercise session. The enrichment analysis was done with DAVID and the graph is plotted in function of the fold enrichment versus Fisher’s exact test P -values. The colors represent if the pathways were overrepresented in up-regulated or down-regulated proteins, while the circle sizes represent the number of regulated proteins in each pathway. b Boxplot of abundance ratios of extracellular matrix (ECM) proteins comparing pre- and post-exercise sessions. Black diamonds represent outlying data points. c Boxplot of abundance ratios of regeneration factors comparing pre- and post-exercise sessions. d ELISA analysis of plasma dermcidin levels prior and after the exercise session. ** P  ≤ 0.01 (Student’s t -test). Down significantly down-regulated molecule, Up significantly up-regulated molecule, ns non-significant

We also investigated the proteins with the most up-regulation following the exercise regimen. Dermcidin, an antimicrobial peptide and regulator of glucose metabolism, was the most up-regulated protein with a 4.4-fold increase in abundance in the proteomics analysis (Fig.  1 c). A validation experiment with ELISA showed a 3.5-fold increase in dermcidin after exercise (Fig.  1 d). Subsequent significant proteins with up-regulation were all growth and tissue regeneration factors, such as somatotropin and several S100 proteins (Fig.  1 c). Histone H4, a major structural protein of cellular chromatins, was up-regulated 3.3-fold (Fig.  1 c). The presence of chromatin proteins in the plasma is surprising to some extent but could be caused by cell lysis. To check this possibility, we looked at the other histones. Histone H2A type 2-C abundance was below the limit of quantification (Additional file 1 : Table S1), while the other core histones that are equally as abundant as H4 in cells, such as H2A, H2B and H3, were not detected. We also found that the two peptides of histone H4 detected in our analysis were from its C-terminal region. The 5 amino acid residues of histone H4 C-terminus correspond to the osteogenic growth peptide, a tissue regeneration factor. Therefore, the identified peptides from histone H4 are probably secreted osteogenic growth peptides rather than leakage of lysed cells. The pathways related to immune response (Fig.  1 a) could also be contributing to tissue repair. Overall, these signatures suggest an acute response to the tissue damage toward regeneration.

The lipidomics analysis showed differential abundance of multiple lipid classes. The sphingolipids [sphingomyelin (SM), ceramides and hexosylceramides], largely driven by SM, have several up-regulated lipid species (Fig.  2 a). Among the phospholipids, diacylglycerophosphoethanolamines (PEs) and monoacylglycerophosphoethanolamines (LPEs) were down-regulated, whereas diacylglycerophosphocholines (PCs), acylalkylglycerophosphocholines (PCOs) and diacylglycerophosphoinositols (PIs) were up-regulated (Fig.  2 a). In terms of energy storage lipids, a decrease of several species of diacylglycerol (DG) and triacylglycerol (TG) (Fig.  2 a). Conversely, TGs containing very long, polyunsaturated fatty acid C22:6 were statistically enriched among the lipids with increased abundance post-exercise (Additional file 1 : Table S5). To better understand this process, we sorted TG species based on their fold change against double bonds or total carbon length. TGs with fewer double bonds had the highest decrease, whereas the more unsaturated ones were up-regulated (Fig.  2 b). TGs with a smaller carbon number also had the highest decrease (Fig.  2 b), suggesting a preference for the degradation of TGs with short saturated fatty acids. One exception to this rule is the TGs with C18:1 and C18:2, which are degraded faster than TGs with C18:0 (Fig.  2 b). In agreement with this observation, the level of oleate (C18:1) was increased by 66% ( P  = 0.001) in plasma compared to non-significant changes of the stearate (C18:0) level ( P  = 0.17) (Fig.  2 b). The lipolysis activator apolipoprotein C3 (found on triglyceride-rich lipoproteins) was up-regulated by 28% ( P  = 0.0002), while the lipolysis marker fatty acid-binding protein 4 was increased by 65% ( P  < 0.001), indicating an increase in lipolysis (Fig.  2 c). Consistently, the lipolysis products glycerol (+ 55%) and fatty acids myristate (C14:0): + 57% ( P  = 0.001), and palmitate (C16:0): + 51% ( P  = 0.004) were also increased post-exercise (Fig.  2 d). The increase in plasma fatty acid levels was accompanied by increase in the levels of 10:1 (+ 53%, P  = 0.003), 12:0 (+ 59%, P  = 0.01), 14:1 (+ 74%, P  = 0.001) and 16:0 (+ 31%, P  = 0.007) acyl-carnitines (Fig.  2 c), which are conjugated molecules that facilitate the transport of fatty acids to the mitochondria for beta oxidation.

Metabolic signatures of the exercise session in the blood plasma. a Plasma lipidomics profile comparing prior and after the exercise session. The bar graph shows the percentage up and down-regulated species in each lipid class. The asterisks represent classes of lipids that are significantly enriched (Fisher’s exact test P  ≤ 0.05) with differential abundant species, as determined using Lipid MiniOn. b Relationship between the total number of double bonds in triacylglycerol species and fold change comparing post- versus pre-exercise. c Relationship between the total number of carbons in fatty acids of triacylglycerol species and fold change comparing post- versus pre-exercise. d Boxplot of abundance ratios of lipid metabolism molecules comparing pre- and post-exercise sessions. Diamonds represent outlying data points. e Levels of molecules from the central carbon metabolism in plasma comparing pre- and post-exercise sessions. f Boxplot of abundance ratios of ATP catabolites in plasma comparing pre- and post-exercise sessions. g Relative quantification of the plasma urea levels using the GC–MS-based metabolomics data. h Quantification of the urine urea concentrations using a colorimetric assay. ALDOA aldolase A, Down significantly (Student’s t -test P  ≤ 0.05) down-regulated molecule, ENO1 enolase 1, HK3 hexokinase 3, IDH1 isocitrate dehydrogenase 1, LDHA lactate dehydrogenase, ns non-significant, PGAM4 phosphoglycerate mutase family member 4, Up significantly up-regulated molecule, ns non-significant, TG triacylglycerol, TKT transketolase

Downstream analysis of the metabolites from central carbon metabolism showed that glucose had only a 7% reduction ( P  = 0.02) in abundance post-exercise (Additional file 1 : Table S6). This small change could be due to the homeostatic mechanisms to maintain the blood glucose levels as we observed changes in D-gluconic acid and in other sugars along with isomerases and kinases (Additional file 1 : Tables S4 and S6). An increase in the levels of the glycolysis products, pyruvate (+ 51%, P  < 0.001) and lactate (+ 34%, P  = 0.02) (Fig.  2 e), was also observed, which agrees with the proteomics data showing enrichment in glycolysis/gluconeogenesis (Fig.  1 a). In addition, we observed 5 out of the 10 glycolytic enzymes being up-regulated: hexokinase HK3, aldolase ALDOA, phosphoglycerate mutase PGAM4, enolase ENO1 and transketolase TKT (Fig.  2 e). A similar increase was observed in the levels of 5 out of 7 TCA cycle intermediates and 2 enzymes in the plasma samples (Fig.  2 e). We also aimed to look for the ATP levels, but neither ATP nor its catabolites were detected by the automated GC-MS analysis. After manual inspection, we found that the increase of glycolysis and TCA cycle metabolites was accompanied by elevated levels of ATP catabolites in plasma: hypoxanthine (+ 11.6-fold, P  < 0.001), xanthine (+ 5.2-fold, P  < 0.001) and inosine (+ 7.3-fold, P  = 0.001) (Fig.  2 f). In terms of amino acids, glutamine, and arginine (detected as ornithine) were reduced by 17% ( P  = 0.003) and 25% ( P  < 0.001), respectively (Additional file 1 : Table S3). Conversely, alanine and glutamate levels were increased by 23% ( P  = 0.01) and 66% ( P  = 0.001) (Additional file 1 : Table S6), while all other detected amino acids had minor or insignificant changes in abundance. To further investigate if amino acids are used as an energy source, we analyzed the levels of their degradation product, urea, in plasma and urine. The levels of urea in plasma and urine were measured by GC-MS and enzymatic assay, respectively, and neither of them showed differences after exercise (Fig.  2 g, h), supporting that amino acid catabolism was not an important source of energy during this exercise session.

Overall, in plasma we observed an increase in ECM (tissue damage markers), immunomodulation and regeneration proteins, suggesting that the impact of exercise causes tissue damage and that the repair response starts immediately. A strong change in lipid metabolism, glycolysis and TCA cycle was observed, probably to support the high energy demands of the body.

Multi-omics signatures of intense exercise in urine

The multi-omics analysis of the urine samples resulted in the identification and quantification of 1711 proteins, 105 metabolites and 279 lipids (Additional file 1 : Tables S7–S9). Out of the molecules, 291 proteins (197 up-regulated and 94 down-regulated), 37 metabolites (14 up-regulated and 23 down-regulated) and 139 lipids (52 up-regulated and 87 down-regulated) were differentially abundant between pre- and post-exercise urine samples. The functional-enrichment analysis showed a strong trend in the regulation of secretion and reabsorption pathways (Fig.  3 a). The renin-angiotensin system pathway, which controls body fluid balance and blood pressure, was enriched 13.6-fold among the post-exercise-regulated proteins (Fig.  3 a). In addition, we found the level of angiotensinogen in urine was increased 2.9-fold after the exercise session, and the levels of its converting enzymes were also consistently increased: angiotensin-converting enzyme (ACE) (detected in 6 samples post-exercise and only 1 before exercise), angiotensin-converting enzyme 2 (ACE2) (+ 2.1-fold, P  = 0.001), Lysosomal Pro-X carboxypeptidase (+ 2.0-fold, P  = 0.02), neprilysin (+ 2.2-fold, P  = 0.0007) and glutamyl aminopeptidase (+ 1.8-fold, P  = 0.02). The level of cathepsin G was reduced by 2.2-fold ( P  = 0.007) and the level of aminopeptidase N was not significantly different ( P  = 0.25) (Fig.  3 b). We observed increases in angiotensin in urine, but not blood or saliva (Fig.  3 c). As the renin-angiotensin pathway increases vasoconstriction, we investigate if it would alter the filtration rates of the kidney, we look at the levels of cystatin C. Cystatin C is a continuously expressed freely filtered small protein used clinically as a marker of glomerular filtration rate. Since cystatin is completely catabolized in the proximal tubules of the kidney, plasma levels of cystatin C are used as clinical biomarker for filtration rates. We found that the level of cystatin C in plasma was similar pre- versus post-exercise session (Fig.  3 d). Similarly, the plasma level of creatinine, another indicator of glomerular filtration rate, was also not significantly affected by the exercise session (Additional file 1 : Table S3). This indicates that glomerular filtration rates are maintained at an approximately constant level during exercise. Conversely, we found an increase in total protein concentration of the urine post-exercise ( P  = 0.0057) (Fig.  3 e), which might indicate an increase in water reabsorption by the renin-angiotensin system to aid in water body homeostasis (i.e., combat water loss due to perspiration).

Comparative multi-omics analysis of urine prior and post exercise. a Functional-enrichment analysis of proteins differentially abundant (Student’s t -test P  ≤ 0.05) after the exercise session. The enrichment analysis was done with DAVID and the graph is plotted in function of the fold enrichment versus Fisher’s exact test P . The colors represent if the pathways were overrepresented in up-regulated or down-regulated proteins, while the circle sizes represent the number of regulated proteins in each pathway. b Boxplot of abundance ratios of renin-angiotensin system proteins comparing pre- and post-exercise sessions. c Boxplot of abundance ratios of angiotensinogen in different body fluids comparing pre- and post-exercise sessions. d Boxplot of abundance ratios of cystatin C in different body fluids comparing pre- and post-exercise sessions. e Protein content in the urine prior to post exercise. ** P  < 0.01 (Student’s t -test). f Boxplot of abundance ratios of transporters comparing pre- and post-exercise sessions. g Boxplot of abundance ratios of urine sugar levels comparing pre- and post-exercise sessions. h Boxplot of abundance ratios of valine pre- and post-exercise session comparing plasma and urine. i Boxplot of abundance ratios of cysteine pre- and post-exercise session comparing plasma and urine. j Urine lipidomics profile comparing prior and after the exercise session. The bar graph shows the percentage up- and down-regulated species in each lipid class. The stars represent classes of lipids that are significantly enriched (Fisher’s exact test P  ≤ 0.05) with differential abundant species, as determined using Lipid MiniOn. k Boxplot of abundance ratios of metabolites comparing pre- and post-exercise sessions. Diamonds represent outlying data. ACE angiotensin converting enzyme, ACE2 angiotensin converting enzyme 2, Biosyn. biosynthesis, Down significantly down-regulated molecule, ns non-significant, PRCP prolylcarboxypeptidase, Prox. tub. proximal tubule, reab. reabsorption, sign. signaling, transp. transporter, Up significantly up-regulated molecule

We next investigated the effect of the renin-angiotensin system regulation in more detail by analyzing the abundance of ion and metabolite transporters. We found a significant change in the abundance of 12 transporters, including 10 up-regulated and 2 down-regulated after exercise (Additional file 1 : Table S4). The abundance of sodium/glucose cotransporters 1 and 5, which are involved in sugar reabsorption, were up-regulated by 2.0- ( P  = 0.05) and 3.3-fold ( P  = 0.0002), respectively (Fig.  3 f). Concomitantly, the level of galactose was reduced by 2.3-fold ( P  = 0.001), while the levels of glucose and fructose remained similar (Fig.  3 g). We also observed an increase in abundance of the sodium/potassium-transporting ATPase (ATP1B1: 2.3-fold, P  < 0.001 and ATP1A1: 2.1-fold, P  = 0.006), while the regulatory subunit γ-2 was down-regulated by 5.9-fold ( P  = 0.009) (Fig.  3 g). In addition, the sodium-coupled monocarboxylate transporters 1 and 2 were up-regulated by 3.4- ( P  = 0.008) and 1.8-fold ( P  = 0.005) (Fig.  3 f), respectively, suggesting a reabsorption of ions and consequently, water. The neutral and basic amino acid reabsorption transport protein rBAT (SLC3A1) was increased by 2.6-fold ( P  < 0.001) after exercise. Conversely, the level of neutral amino acid transporter 10 (SLC38A10) was reduced by 1.1-fold ( P  = 0.01) (Fig.  3 f). Most of the amino acids had similar post-/pre-exercise fold changes comparing plasma with urine (Fig.  3 h and Additional file 1 : Table S6). However, there were amino acids, such as cysteine, which responded differently in plasma than in urine. Cysteine abundance increased 29% ( P  = 0.003) post-/pre-exercise in urine while plasma levels remained similar (Fig.  3 i). These data support differential reabsorption of amino acids during exercise.

In terms of energy-related metabolites, the lipidomics analysis of urine showed a strikingly different profile compared with the plasma samples. Despite similarly higher levels of acyl-carnitines and ceramides in urine and plasma, the levels of TG, SM, PC, PCO and PI were divergent in these biofluids (Figs.  2 a and 3 j). TG levels were higher in urine, while the levels of SM, PC, PCO and PI were lower (Fig.  3 j). These differences in lipid profiles between plasma and urine might be due to filtration, reabsorption, and differences in energetic demands locally in the kidneys. The glycolysis products, lactate and pyruvate, were increased by 4.7- ( P  = 0.001) and 2.2-fold ( P  = 0.0004), respectively (Fig.  3 k). On the other hand, the levels of most the TCA cycle intermediates (Additional file 1 : Table S3) were similar before and after exercise, like that of α-ketoglutarate (Fig.  3 k). The levels of the ATP catabolites, xanthine, hypoxanthine, and inosine, were increased after exercise, while the level of uric acid was decreased at the same time (Fig.  3 k). Collectively, the observed increases in urinary catabolites are consistent with a urinary molecular signature of an increase of the energy utilization.

Our data showed a simultaneous and consistent molecular signature of energy utilization and catabolite excretion in the plasma and urine. We also observed increases in the renin-angiotensin system and nutrient re-absorption system proteins, consistent with an adaption to maintain fluid balance and meet the increased energy demands of exercise.

Multi-omics signatures of intense exercise in saliva

The multi-omic analysis of the saliva samples resulted in the identification and quantification of 2339 human proteins, 93 metabolites and 410 lipids (Additional file 1 : Tables S10–S12). Of these molecules, 487 proteins (92 up-regulated and 395 down-regulated), 7 metabolites (4 up-regulated and 3 down-regulated) and 122 lipids (68 up-regulated and 54 down-regulated) were significantly regulated in response to the exercise regimen. A functional-enrichment analysis with DAVID showed 23 pathways to be overrepresented in proteins regulated by the exercise session. We found an overrepresentation of down-regulated proteins from highly abundant intracellular pathways, such as ribosome, proteasome, carbon metabolism, gap junctions and aminoacyl-tRNA synthesis (Fig.  4 a, b). In contrast, the level of lysozyme, which is produced by the submaxillary gland and directly secreted into saliva, was not significantly affected by exercise (Fig.  4 b). The consistent decrease in proteins from several abundant intracellular pathways post- versus pre-exercise may suggest a reduction of the cell numbers in saliva. A 17% ( P  = 0.01) reduction in the epithelial cell marker protein 1 (also known as 14-3-3 sigma) was observed while the myeloid cell marker CD14 level increased by 40% ( P  = 0.02) (Fig.  4 b), suggesting that the decrease in abundant cellular proteins may be due to a reduction of epithelial cell shedding into saliva.

Comparative multi-omics analysis of saliva prior and post exercise. a Functional-enrichment analysis of proteins differentially abundant ( Student’s t -test P  ≤ 0.05) after the exercise session. The enrichment analysis was done with DAVID and the graph is plotted in function of the fold enrichment versus Fisher’s exact test P -values. The colors represent if the pathways were overrepresented in up-regulated or down-regulated proteins, while the circle sizes represent the number of regulated proteins in each pathway. b Boxplot of abundance ratios of abundant intracellular proteins comparing pre- and post-exercise sessions. Diamonds represent outlying data points. c Boxplot of abundance ratios of inflammation and fluid balance comparing pre- and post-exercise sessions. d Saliva lipidomics profile comparing prior and after the exercise session. The bar graph shows the percentage of up and down-regulated (Student’s t -test P  ≤ 0.05) species in each lipid class. The stars represent classes of lipids that are significantly enriched (Fisher’s exact test P  ≤ 0.05) with differential abundant species, as determined using Lipid MiniOn. Down down-regulated molecule, init. initiation, Up up-regulated molecule, ns non-significant

We also observed a decrease in the levels of the pro-inflammatory cytokines IL-36α, IL-18, and IL-1 (Fig.  4 c). This was accompanied by a decrease in the level of ceramides (Fig.  4 d), which are also pro-inflammatory molecules. Consistent with this observation, ceramide synthase 3 was also reduced after exercise (Fig.  4 c). We also observed an increase in levels of anti- or post-inflammatory lipid species, such as monoalkylglycerophosphocholines (also known as lyso-PAF) and TGs (Fig.  4 d). These data show a coordinated reduction of inflammation post-exercise, which is further supported by a reduction in the leukocyte trans-endothelial migration pathway (Fig.  4 a). One possibility is that this reduction in inflammation facilitates gas exchange since airway inflammation may induce bronchoconstriction or obstructive airflow patterns. However, salivary biomarker composition may not be reflective of that found within nasal secretions, lower respiratory tract secretions or alveolar lung fluid. Thrombospondim-1, an inducer of the pulmonary vasoconstriction, was up-regulated by 57% ( P  = 0.04) after exercise, while opiorphin prepropeptide, a vasodilator of the peripheral tissue, was up-regulated by 60% ( P  = 0.02) (Fig.  4 c. We also observed an up-regulation of secreted phospholipase A2 (PLA2G2) (Fig.  4 c and its products monoacylglycerophosphocholines (also known as lysoPCs) (Fig.  4 d), which are vasorelaxation inhibitors. Though speculative, these data support the idea that inflammation is reduced in the oral cavity and possibly in the airways as a temporary adaptive mechanism to improve respiratory performance during intense physical activity.

We hypothesized that the anti-inflammatory processes might influence susceptibility to infection and trigger a compensating change in other immune system elements. To address this hypothesis, we investigated levels of other immune proteins. Several innate immune proteins were consistently up-regulated after exercise: CD14, CD55 and all antimicrobial peptides/proteins (dermcidin, cystatins, β-defensin 1 and histatin-1) (Fig.  5 a). We validated the levels of dermcidin by ELISA. Dermcidin had a 2.5-increase in the proteomics ( P  = 0.01) and a 10.7-fold increase by ELISA ( P  < 0.001) (Fig.  5 a, b). The discrepancy in fold change might be due to the levels of dermcidin being close to the detection limit in the pre-exercise sample. This increase in antimicrobial peptides in saliva supports our hypothesis of a compensatory mechanism to improve host defense. We next explored whether there was a functional impact on the oral microbiota. Compared to plasma and urine, we found higher levels of C15 fatty acyl-containing PE and diacylglycerophosphoglycerol (PG) (Fig.  5 c), in saliva than in blood and urine, consistent with the expectedly higher load of bacteria in the oral cavity. We reanalyzed the proteomics data by searching against the human and oral microbiome bacterial sequences. We identified proteins from 142 bacterial genera, and we used the intensity-based absolute quantification (iBAQ) method to estimate the relative protein copy numbers. The saliva proteome was comprised of 96.3% human and 3.7% bacterial proteins by copy numbers (Fig.  5 d). We used the same quantification to calculate the saliva protein fraction from each organism and compared prior and after the exercise. The exercise session had no effect on the human proteins and the total bacterial proteins, but decreased the abundance of the bacteria Cryptobacterium curtum , Propionibacterieae G-2, Absconditabacteria SR1 G-1 and Chlorobium limicola (Fig.  5 e). The decreases in these four oral cavity bacteria are consistent with our hypothesis that increases in salivary antimicrobial peptides influence oral microbial populations and potentially host susceptibility.

Analysis of the saliva innate immune proteins and microbiota prior and post exercise. a Boxplot of abundance ratios of innate immune proteins comparing pre- and post-exercise sections. Stars represent outliers. b ELISA analysis of saliva dermcidin levels prior and after the exercise sessions. ** P  ≤ 0.01 (Student’s t -test). c Number of diacylglycerophosphoethanolamine and diacylglycerophosphoglycerol species containing C15 fatty acids in different body fluids. ** P  ≤ 0.01 (Fisher’s exact test). d Fraction of human and bacterial proteins in the saliva proteomics. e Boxplot of abundance ratios of total iBAQ scores from proteins of different organisms comparing pre- and post-exercise sessions. Stars represent outliers. Down significantly down-regulated molecule, PE diacylglycerophosphoethanolamine, PG diacylglycerophosphoglycerol, Up significantly up-regulated molecule, ns non-significant

Overall, we observed molecular signatures of down-regulation of inflammation in the saliva, which can be an adaptive response to exercise that improves respiration and blood flow. We also found evidence that the decrease in inflammation is accompanied by an increase of antimicrobial peptides, which altered oral microbiome composition.

Our study illustrates the promise of utilizing advanced mass spectrometry for the global characterization of proteins, lipids, and metabolites to understand the coordinated physiologic and immunologic acute response to intense exercise. In plasma, we observed molecular signatures consistent with those reported in previous studies despite differences in the exercise regimen and cohort characteristics divergent enough to have a significant influence on tissue responses to exercise [ 5 , 11 ]. Lewis et al. [ 11 ] performed a pre- and post-exercise plasma metabolomics analysis of marathon runners, individuals that were submitted to an acute exercise regimen or running a marathon, whereas Contrepois et al. [ 5 ] performed a multi-omics analysis of plasma after volunteers reached “peak oxygen consumption” in a short and intense exercise session (8–12 min exercise). In both studies, the average age was in the 50 s, whereas in our cohort the average age was in the 20 s. Like what was reported by Contrepois et al. [ 5 ], plasma from volunteers in our study showed signatures of tissue damage and regenerative response after exercise. In terms of metabolism, all three studies showed increased lipolysis [ 5 , 11 ]. We found that short-chain saturated fatty acids were consumed first, consistent with previous findings [ 5 ]. Longer and unsaturated fatty acids were metabolized more slowly, except for C18:1 and C18:2, which are rapidly metabolized like the short saturated fatty acids. Short- and mid-chain fatty acids can be metabolized faster as a result of their carnitine-independent transportation into mitochondria [ 37 ]. Unsaturated fatty acids are harder to metabolize due to the requirement of additional beta oxidation steps in the mitochondria [ 38 ]. Beta oxidation is accompanied by an increase in the TCA cycle activity. Simultaneously, we observed molecular markers of an increase in glycolysis metabolites, evidenced by the accumulation of its products lactate and pyruvate, but the minimum change in the levels of glucose. Stable levels of plasma glucose are likely the result of a homeostatic mechanism that mobilizes glucose from glycogen stores [ 11 ]. Another mechanism could be via dermcidin. Although, dermcidin is mainly characterized as an antimicrobial molecule, more recently it was suggested to play a role in glucose homeostasis by reducing insulin secretion [ 39 ].

A major difference between our study and the studies by Lewis et al. [ 11 ] and Contrepois et al. [ 5 ] was the magnitude of amino acid consumption. While the two prior studies showed that amino acid degradation occurs during the exercise session, this was not evident in our study, which we attribute to differences in age, exercise regimen and training of the cohort. Younger and well-trained individuals have lower amino acid demands during exercise [ 40 ]. In addition, amino acid metabolism is not altered in resistance exercise [ 40 ]. The increase in alanine and glutamate observed in our analysis is probably due to transamination of the overflowing glycolysis and TCA cycle metabolites pyruvate and α-ketoglutarate [ 41 ]. In a parallel study, we analyzed the effects of heat stress on a moderate exercise regimen in which participants walked on the treadmill for 1 h at 5 km/h. We found that only lipid metabolism was regulated during this exercise and no significant difference was observed in glycolysis or amino acid metabolism, when we compared post- and pre-exercise results (unpublished observations). This further supports that exercise regimen can differentially regulate different metabolic pathways.

Increased metabolism supporting the energy demands of exercise leads to higher production of catabolites that must then be excreted in the urine. We found increased levels of the glycolysis products (lactate and pyruvate) and ATP catabolites (inosine, xanthine, and hypoxanthine) in the post-exercise urine. Consistent with our data, these metabolites have been reported to increase after different exercise regimens [ 42 , 43 , 44 ]. Stable plasma levels of cystatin C and creatinine were consistent with unchanged glomerular filtration rates after the firefighter training regimen. Others have reported stable glomerular filtration rate even during extreme physical activity, such as running an ultramarathon [ 45 ]. We found increases in molecular markers of the renin-angiotensin system in the urine, but not in plasma and saliva. Two other exercise regimens, high-intensity intermittent exercise and moderate-intensity continuous exercise, have both displayed an increase in levels of angiotensin II and angiotensin 1–7 in urine but not in plasma [ 46 ]. This is consistent with up-regulation being isolated to the proximal tubule rather than associated with other sources like the liver [ 47 ]. Angiotensin is produced in the proximal tubule of the kidney, which may explain the observed increase in urine. Angiotensin II increases the expression of sodium-glucose cotransporters, increasing renal reabsorption of sugars and water [ 48 ]. The increased angiotensin II produced in the kidneys may cause vasoconstriction as shown in rats [ 49 ]. Conversely, there is vasodilation in the muscles during exercise [ 50 , 51 , 52 ], which may help diverge the blood flow and supply nutrients and oxygen to the contracting muscle.

Moderate aerobic exercise has also been shown to improve respiratory mechanics and possibly lung function [ 53 ]. We found that the decrease in inflammatory markers was accompanied by increased opiorphin, a peripheral tissue vasodilator [ 54 ] that may increase blood flow to muscles during the exercise regimen to improve the delivery of oxygen and nutrients [ 52 ]. Our saliva analysis showed a decrease in abundant cellular proteins, which might be due to a reduction in normal epithelial cell turnover in the oral cavity [ 55 ]. Nonetheless, moderate aerobic exercise has been shown to decrease eosinophilic inflammation in a murine model of asthma [ 56 ]. Airway inflammation caused by allergies, asthma, or chronic obstructive pulmonary disease (COPD) can lead to bronchoconstriction, airflow obstruction and decreases in lung function [ 57 ]. We postulate that the decrease in inflammatory molecules we observed in the saliva after exercise might represent an adaptive mechanism to improve gas exchange in response to higher cellular oxygen demand [ 58 , 59 ]. Furthermore, during strenuous activity, dominant nasal breathers will switch to oronasal breathing at an approximated 35 L/min threshold [ 60 , 61 ]. At maximum minute ventilation, nasal breathing accounts for approximately 60% of total ventilation; suggesting that the crucial functions of nasopharyngeal filtration, warming and humidification are reduced. Oronasal breathing allows for greater distal airway deposition of microbes, allergens and toxic/irritant particles as mucociliary nasopharyngeal membranes are bypassed [ 62 ]. In addition, inhaled air is drier and cooler, which may increase the risk for epithelial cellular damage, encumber mucociliary escalator function, and increase infection susceptibility as an intact epithelial barrier is essential for preventing respiratory infections.

Decreased proinflammatory markers in the oral cavity might also impact the ability to fight against infections. Indeed, marathon runners are at a higher risk for acquiring upper respiratory tract infections after races [ 63 ]. We found that decreases in the proinflammatory response occurred alongside increases in antimicrobial peptides and CD14 within the oral cavity. We interpreted these changes as evidence of a compensatory mechanism to maintain immune surveillance. The reduction of specific microbes from the oral microbiome may be a consequence of this increase in antimicrobial peptides. In fact, increases in salivary antimicrobial peptides have been previously linked to prolonged exercise. However, this increase in antimicrobial peptides had no effect on inhibiting E. coli growth [ 64 ], suggesting a limited capacity of antimicrobial peptides within the oral cavity to protect against host infections. It is plausible that our observed increase in antimicrobial peptide expression was insufficient to compensate for the expected reduction in immune surveillance in the presence of the decreased proinflammatory response.

To study potential impacts on the saliva immune molecule profiles in response to the high-intensity of physical activity we performed a systematic literature review. We queried PubMed for papers that studied respiratory infection events in response to a high-intensity physical activity (see Table  1 for keywords), which included firefighters, soldiers, marathon runners and soccer players. Only papers that performed a survey of respiratory illnesses were qualified for the systematic review. Gaughan et al. [ 65 ], monitored a group of 58 wildland firefighters post-fire and compared respiratory questionnaire results to pre- and post-fire season responses. They found that respiratory symptom scores were significantly higher post-fire compared to pre-season and post-season. Similarly, Tiollier et al. [ 66 ] performed medical examinations and monitored salivary immunoglobulin A (IgA) levels for a group of 21 soldiers throughout an intense period of training. They found that over 66% experienced at least one upper respiratory tract infection episode which rapidly resolved 2 d after the training session. Robson-Ansley et al. [ 67 ], Peters et al. [ 68 ], and Nieman et al. [ 69 ] followed up on post-marathon runner upper respiratory symptomology via questionnaire. All three studies found at least twice higher incidence of self-reported upper respiratory infections compared to control groups. However, Robson-Ansley et al. [ 67 ], attributed respiratory symptomology to elevated immunoglobulin E (IgE) serum levels, suggesting that respiratory symptomology was due to eosinophilic inflammation rather than neutrophilic inflammation. Furusawa et al. [ 70 ] found no significant differences in upper respiratory tract infection rates in a cohort of wheelchair marathon racers. Conversely, Moreira et al. [ 71 ] monitored salivary IgA, salivary cortisol, and upper respiratory tract infection symptoms within a cohort of 34 soccer players during practice season, competition and post-season. They found that the number of upper respiratory symptoms significantly reduced, while salivary IgA significantly increased 2 weeks after the competition season ended. They concluded that intense training and competition may attenuate mucosal immune responses and neutrophilic inflammation. In summary, there is evidence supporting a relationship between physical demands and a higher incidence of respiratory infections.

Our study had limitations that potentially reduced the generalizability of our results. Study participants had a relatively low diversity being historically healthy, athletically fit, young adult males. They were chosen from an available small sample of local wildland firefighters. The study did not include women, which is a reflex of the firefighter population in the US which is composed of 96% males [ 72 ]. The small sample size might bring concerns of findings statistical significance and interference with confounding factors, but the “within subject” differential expression before and after intense exercise reduces the impact of the sample size. In addition, we estimated that the study was sufficiently powered for its intended aims. Increasing the number of subjects could increase the number of identified lipids, proteins, and metabolites, but would not change the main conclusions of the paper. Moreover, a metabolomics analysis of plasma showed strikingly similar profiles and trends in terms of lipolysis, glycolysis, TCA cycle, tissue damage and regeneration response when compared to other exercise metabolomic studies [ 5 , 11 ]. Unlike Contrepois et al. [ 5 ], our exercise protocols were not standardized, and peak oxygen consumption (VO 2 max) was not measured to monitor whether participants reached their maximal exercise capacity during the 45 min exercise session. However, the accumulation of lactate is a reliable indicator of anaerobic metabolism, suggesting that exercise intensity had surpassed aerobic respiratory capacity in most of our participants [ 73 ]. It is also important to note that clinical trials should be carried out before using these findings for human health.

Another overriding limitation would be the generalizability of potential health impacts to the general population or other elite athlete exercise multi-omic studies because of the characteristics of the different populations. Nonetheless, when we compared our results to those considered in the systematic review cohorts, we did observe a similar trend regarding possible increased susceptibility to respiratory infection after intense physical activity. Unfortunately, four of the seven studies examined, relied upon self-reported respiratory symptoms to indicate respiratory infection incidence. While self-reporting through questionnaires is a common method to collect health information, it may not be the most accurate or consistent method. The presence of respiratory symptoms does not differentially diagnose respiratory infection. Additionally, self-report of symptoms is subject to recall bias and makes it more difficult to obtain consistent outcomes across a study because respiratory symptoms also occur during eosinophilic inflammation or hypersensitivity reactions. However, one of the reviewed studies considered the presence of fever obtained during medical examination, as well as respiratory symptoms to diagnose respiratory infection. This helped to reduce bias and disease misclassification [ 68 ].

One final limitation that may be unique to wildland firefighters, is their perennial exposure to specific respirable toxic pollutants during fire suppression activities [ 74 , 75 ]. These individual environmental exposures may permanently alter immune system immunomodulation and gene expression of key metabolic pathways to confound our results. Further epigenetics investigation would help to illuminate this potential bias.

Conclusions

Overall, we observed clear evidence for the regulation of physiological and biochemical processes typically coordinated to supply energy and oxygen demands from intense exercise. In plasma, we found signatures of tissue damage and an acute repair response. In terms of metabolism, lipolysis, glycolysis, and TCA cycle were up-regulated to meet increased energy demands. The urine analysis showed a strong regulation of the renin-angiotensin system toward an adaptive response required to increase catabolite elimination, reabsorption of nutrients and maintain fluid balance. Decreases in inflammatory molecules and increases in antimicrobial peptides in saliva could be viewed as paired responses, one to improve respiratory function, and the other to increase immune surveillance under conditions of increased susceptibility to infection. Furthermore, we also found that this compensatory mechanism might be insufficient to protect professionals after tasks that demand intense physical effort. This study is a critical first step towards developing a comprehensive understanding of the physiological, biochemical, and immunological effects of stress, definition of the molecular markers of those effects, and the development of effective methods for monitoring and mitigating those effects in critical first responder populations like firefighters.

Availability of data and material

The raw LC-MS/MS proteomics data files are publicly available at ProteomeXchange-associated Pride data repository under the accession numbers PXD020122, PXD020131, PXD020164 and PXD020352. All raw lipidomics and metabolomics data files are publicly available at MetaboLights data repository under the accession number MTBLS1891.

Abbreviations

Angiotensin-converting enzyme

Angiotensin-converting enzyme 2

Chronic obstructive pulmonary disease

Diacylglycerol

Extracellular matrix

Ethylenediaminetetraacetic acid

Gas chromatography-mass spectrometry heavy isotope internal standard mix

Gas chromatography-mass spectrometry

Intensity-based absolute quantification

Immunoglobulin A

Immunoglobulin E

Liquid chromatography-tandem mass spectrometry

Monoacylglycerophosphoethanolamine

N -Methyl- N -(trimethylsilyl)trifluoroacetamide

Diacylglycerophosphocholine

Acylalkylglycerophosphocholine

Diacylglycerophosphoethanolamine

Diacylglycerophosphoglycerol

Diacylglycerophosphoinositol

Robust Mahalanobis distance based on peptide abundance vectors

Sphingomyelin

Statistical procedure for the analyses of peptide abundance normalization strategies

Tricarboxylic acid

Triacylglycerol

Trimethylchlorosilane

Tandem mass tags

Peak oxygen consumption

Hawley JA, Hargreaves M, Joyner MJ, Zierath JR. Integrative biology of exercise. Cell. 2014;159(4):738–49.

Article   PubMed   CAS   Google Scholar  

Friganovic A, Selic P, Ilic B, Sedic B. Stress and burnout syndrome and their associations with coping and job satisfaction in critical care nurses: a literature review. Psychiatr Danub. 2019;31(Suppl 1):21–31.

PubMed   Google Scholar  

Adrian AL, Skeiky L, Burke TM, Gutierrez IA, Adler AB. Sleep problems and functioning during initial training for a high-risk occupation. Sleep Health. 2019;5(6):651–7.

Article   PubMed   Google Scholar  

Sugden C, Athanasiou T, Darzi A. What are the effects of sleep deprivation and fatigue in surgical practice?. Semin Thorac Cardiovasc Surg. 2012;24(3):166–75.

Contrepois K, Wu S, Moneghetti KJ, Hornburg D, Ahadi S, Tsai MS, et al. Molecular choreography of acute exercise. Cell. 2020;181(5):1112-30.e16.

Article   PubMed   PubMed Central   CAS   Google Scholar  

Geyer PE, Kulak NA, Pichler G, Holdt LM, Teupser D, Mann M. Plasma proteome profiling to assess human health and disease. Cell Syst. 2016;2(3):185–95.

Guijas C, Montenegro-Burke JR, Cintron-Colon R, Domingo-Almenara X, Sanchez-Alavez M, Aguirre CA, et al. Metabolic adaptation to calorie restriction. Sci Signal. 2020;13(648):eabb490.

Article   Google Scholar  

Keshishian H, Burgess MW, Specht H, Wallace L, Clauser KR, Gillette MA, et al. Quantitative, multiplexed workflow for deep analysis of human blood plasma and biomarker discovery by mass spectrometry. Nat Protoc. 2017;12(8):1683–701.

Liu Y, Buil A, Collins BC, Gillet LC, Blum LC, Cheng LY, et al. Quantitative variability of 342 plasma proteins in a human twin population. Mol Syst Biol. 2015;11(1):786.

Article   PubMed   PubMed Central   Google Scholar  

Wu C, Duan J, Liu T, Smith RD, Qian WJ. Contributions of immunoaffinity chromatography to deep proteome profiling of human biofluids. J Chromatogr B Analyt Technol Biomed Life Sci. 2016;1021:57–68.

Lewis GD, Farrell L, Wood MJ, Martinovic M, Arany Z, Rowe GC, et al. Metabolic signatures of exercise in human plasma. Sci Transl Med. 2010;2(33):33ra7.

De Miguel Z, Khoury N, Betley MJ, Lehallier B, Willoughby D, Olsson N, et al. Exercise plasma boosts memory and dampens brain inflammation via clusterin. Nature. 2021;600(7889):494–9.

Scheiman J, Luber JM, Chavkin TA, Macdonald T, Tung A, Pham LD, et al. Meta-omics analysis of elite athletes identifies a performance-enhancing microbe that functions via lactate metabolism. Nat Med. 2019;25(7):1104–9.

Horowitz AM, Fan X, Bieri G, Smith LK, Sanchez-Diaz CI, Schroer AB, et al. Blood factors transfer beneficial effects of exercise on neurogenesis and cognition to the aged brain. Science. 2020;369(6500):167–73.

Incident management situation report. 2020. https://famprod.nwcg.gov/batchout/IMSRS_from_1990_to_2022/2020/ . Accessed 7 Aug 2023.

Nakayasu ES, Nicora CD, Sims AC, Burnum-Johnson KE, Kim YM, Kyle JE, et al. MPLEx: a robust and universal protocol for single-sample integrative proteomic, metabolomic, and lipidomic analyses. mSystems. 2016;1(3):e00043–16.

Wang Y, Yang F, Gritsenko MA, Wang Y, Clauss T, Liu T, et al. Reversed-phase chromatography with multiple fraction concatenation strategy for proteome profiling of human MCF10A cells. Proteomics. 2011;11(10):2019–26.

Mertins P, Tang LC, Krug K, Clark DJ, Gritsenko MA, Chen L, et al. Reproducible workflow for multiplexed deep-scale proteome and phosphoproteome analysis of tumor tissues by liquid chromatography-mass spectrometry. Nat Protoc. 2018;13(7):1632–61.

Nakayasu ES, Syed F, Tersey SA, Gritsenko MA, Mitchell HD, Chan CY, et al. Comprehensive proteomics analysis of stressed human islets identifies GDF15 as a target for type 1 diabetes intervention. Cell Metab. 2020;31(2):363–74.

Mayampurath AM, Jaitly N, Purvine SO, Monroe ME, Auberry KJ, Adkins JN, et al. DeconMSn: a software tool for accurate parent ion monoisotopic mass determination for tandem mass spectra. Bioinformatics. 2008;24(7):1021–3.

Petyuk VA, Mayampurath AM, Monroe ME, Polpitiya AD, Purvine SO, Anderson GA, et al. DtaRefinery, a software tool for elimination of systematic errors from parent ion mass measurements in tandem mass spectra data sets. Mol Cell Proteom. 2010;9(3):486–96.

Article   CAS   Google Scholar  

Kim S, Pevzner PA. MS-GF + makes progress towards a universal database search tool for proteomics. Nat Commun. 2014;5:5277.

Monroe ME, Shaw JL, Daly DS, Adkins JN, Smith RD. MASIC: a software program for fast quantitation and flexible visualization of chromatographic profiles from detected LC-MS(/MS) features. Comput Biol Chem. 2008;32(3):215–7.

Tyanova S, Temu T, Cox J. The MaxQuant computational platform for mass spectrometry-based shotgun proteomics. Nat Protoc. 2016;11(12):2301–19.

Gibbons BC, Chambers MC, Monroe ME, Tabb DL, Payne SH. Correcting systematic bias and instrument measurement drift with mzRefinery. Bioinformatics. 2015;31(23):3838–40.

Grassl N, Kulak NA, Pichler G, Geyer PE, Jung J, Schubert S, et al. Ultra-deep and quantitative saliva proteome reveals dynamics of the oral microbiome. Genome Med. 2016;8(1):44.

Kim YM, Schmidt BJ, Kidwai AS, Jones MB, Deatherage Kaiser BL, Brewer HM, et al. Salmonella modulates metabolism during growth under conditions that induce expression of virulence genes. Mol Biosyst. 2013;9(6):1522–34.

Hiller K, Hangebrauk J, Jager C, Spura J, Schreiber K, Schomburg D. MetaboliteDetector: comprehensive analysis tool for targeted and nontargeted GC/MS based metabolome analysis. Anal Chem. 2009;81(9):3429–39.

Kind T, Wohlgemuth G, Lee DY, Lu Y, Palazoglu M, Shahbaz S, et al. FiehnLib: mass spectral and retention index libraries for metabolomics based on quadrupole and time-of-flight gas chromatography/mass spectrometry. Anal Chem. 2009;81(24):10038–48.

Dautel SE, Kyle JE, Clair G, Sontag RL, Weitz KK, Shukla AK, et al. Lipidomics reveals dramatic lipid compositional changes in the maturing postnatal lung. Sci Rep. 2017;7:40555.

Pluskal T, Castillo S, Villar-Briones A, Oresic M. MZmine 2: modular framework for processing, visualizing, and analyzing mass spectrometry-based molecular profile data. BMC Bioinf. 2010;11:395.

Stratton KG, Webb-Robertson BM, Mccue LA, Stanfill B, Claborne D, Godinez I, et al. pmartR: quality control and statistics for mass spectrometry-based biological data. J Proteome Res. 2019;18(3):1418–25.

Matzke MM, Waters KM, Metz TO, Jacobs JM, Sims AC, Baric RS, et al. Improved quality control processing of peptide-centric LC-MS proteomics data. Bioinformatics. 2011;27(20):2866–72.

Webb-Robertson BJ, Matzke MM, Jacobs JM, Pounds JG, Waters KM. A statistical selection strategy for normalization procedures in LC-MS proteomics experiments through dataset-dependent ranking of normalization scaling factors. Proteomics. 2011;11(24):4736–41.

Da Huang W, Sherman BT, Lempicki RA. Bioinformatics enrichment tools: paths toward the comprehensive functional analysis of large gene lists. Nucleic Acids Res. 2009;37(1):1–13.

Clair G, Reehl S, Stratton KG, Monroe ME, Tfaily MM, Ansong C, et al. Lipid Mini-On: mining and ontology tool for enrichment analysis of lipidomic data. Bioinformatics. 2019;35(21):4507–8.

Schonfeld P, Wojtczak L. Short- and medium-chain fatty acids in energy metabolism: the cellular perspective. J Lipid Res. 2016;57(6):943–54.

Schulz H. Beta oxidation of fatty acids. Biochim Biophys Acta Mol Cell Biol Lipids. 1991;1081(2):109–20.

Bhattacharya S, Khan MM, Ghosh C, Bank S, Maiti S. The role of dermcidin isoform-2 in the occurrence and severity of Diabetes. Sci Rep. 2017;7(1):8252.

Rennie MJ, Tipton KD. Protein and amino acid metabolism during and after exercise and the effects of nutrition. Annu Rev Nutr. 2000;20:457–83.

Felig P, Wahren J. Amino acid metabolism in exercising man. J Clin Invest. 1971;50(12):2703–14.

Calles-Escandon J, Cunningham JJ, Snyder P, Jacob R, Huszar G, Loke J, et al. Influence of exercise on urea, creatinine, and 3-methylhistidine excretion in normal human subjects. Am J Physiol. 1984;246(4 Pt 1):E334–8.

PubMed   CAS   Google Scholar  

Sun T, Wu Y, Wu X, Ma H. Metabolomic profiles investigation on athletes’ urine 35 minutes after an 800-meter race. J Sports Med Phys Fit. 2017;57(6):839–49.

Google Scholar  

Pechlivanis A, Papaioannou KG, Tsalis G, Saraslanidis P, Mougios V, Theodoridis GA. Monitoring the response of the human urinary metabolome to brief maximal exercise by a combination of RP-UPLC-MS and 1 H NMR spectroscopy. J Proteome Res. 2015;14(11):4610–22.

Wolyniec W, Ratkowski W, Kasprowicz K, Jastrzebski Z, Malgorzewicz S, Witek K, et al. Glomerular filtration rate is unchanged by ultramarathon. J Strength Cond Res. 2018;32(11):3207–15.

Magalhaes DM, Nunes-Silva A, Rocha GC, Vaz LN, De Faria MHS, Vieira ELM, et al. Two protocols of aerobic exercise modulate the counter-regulatory axis of the renin-angiotensin system. Heliyon. 2020;6(1):e03208.

Nehme A, Zouein FA, Zayeri ZD, Zibara K. An update on the tissue renin angiotensin system and its role in physiology and pathology. J Cardiovasc Dev Dis. 2019;6(2):14.

PubMed   PubMed Central   CAS   Google Scholar  

Bautista R, Manning R, Martinez F, Avila-Casado Mdel C, Soto V, Medina A, et al. Angiotensin II-dependent increased expression of Na + -glucose cotransporter in hypertension. Am J Physiol Renal Physiol. 2004;286(1):F127–33.

Maeda S, Iemitsu M, Jesmin S, Miyauchi T. Acute exercise causes an enhancement of tissue renin-angiotensin system in the kidney in rats. Acta Physiol Scand. 2005;185(1):79–86.

Stebbins CL, Symons JD. Role of angiotensin II in hemodynamic responses to dynamic exercise in miniswine. J Appl Physiol. 1995;78(1):185–90.

Brothers RM, Haslund ML, Wray DW, Raven PB, Sander M. Exercise-induced inhibition of angiotensin II vasoconstriction in human thigh muscle. J Physiol. 2006;577(Pt 2):727–37.

Joyner MJ, Casey DP. Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs. Physiol Rev. 2015;95(2):549–601.

Chlif M, Chaouachi A, Ahmaidi S. Effect of aerobic exercise training on ventilatory efficiency and respiratory drive in obese subjects. Respir Care. 2017;62(7):936–46.

Fu S, Tar MT, Melman A, Davies KP. Opiorphin is a master regulator of the hypoxic response in corporal smooth muscle cells. FASEB J. 2014;28(8):3633–44.

Squier CA, Kremer MJ. Biology of oral mucosa and esophagus. J Natl Cancer Inst Monogr. 2001;29:7–15.

Vieira RP, Claudino RC, Duarte AC, Santos AB, Perini A, Faria Neto HC, et al. Aerobic exercise decreases chronic allergic lung inflammation and airway remodeling in mice. Am J Respir Crit Care Med. 2007;176(9):871–7.

Barnes PJ. Immunology of asthma and chronic obstructive pulmonary disease. Nat Rev Immunol. 2008;8(3):183–92.

Bousquet J, Jeffery PK, Busse WW, Johnson M, Vignola AM. Asthma: from bronchoconstriction to airways inflammation and remodeling. Am J Respir Crit Care Med. 2000;161(5):1720–45.

Hancox RJ, Poulton R, Greene JM, Filsell S, Mclachlan CR, Rasmussen F, et al. Systemic inflammation and lung function in young adults. Thorax. 2007;62(12):1064–8.

Lacomb CO, Tandy RD, Ping Lee S, Young JC, Navalta JW. Oral versus nasal breathing during moderate to high intensity submaximal aerobic exercise. IJKSS. 2017;5(1):8–16.

Niinimaa V, Cole P, Mintz S, Shephard RJ. Oronasal distribution of respiratory airflow. Respir Physiol. 1981;43(1):69–75.

Clark KA, Rogers KS. The respiratory system. In: Racz L, Yamamoto D, Eninger RM, editors. The respiratory protection handbook: safeguarding against current and emerging hazards. 1st ed. Boca Raton: CRP Press; 2017.

Nieman DC. Risk of upper respiratory tract infection in athletes: an epidemiologic and immunologic perspective. J Athl Train. 1997;32(4):344–9.

Davison G, Allgrove J, Gleeson M. Salivary antimicrobial peptides (LL-37 and alpha-defensins HNP1-3), antimicrobial and IgA responses to prolonged exercise. Eur J Appl Physiol. 2009;106(2):277–84.

Gaughan DM, Cox-Ganser JM, Enright PL, Castellan RM, Wagner GR, Hobbs GR, et al. Acute upper and lower respiratory effects in wildland firefighters. J Occup Environ Med. 2008;50(9):1019–28.

Tiollier E, Gomez-Merino D, Burnat P, Jouanin JC, Bourrilhon C, Filaire E, et al. Intense training: mucosal immunity and incidence of respiratory infections. Eur J Appl Physiol. 2005;93(4):421–8.

Robson-Ansley P, Howatson G, Tallent J, Mitcheson K, Walshe I, Toms C, et al. Prevalence of allergy and upper respiratory tract symptoms in runners of the London marathon. Med Sci Sports Exerc. 2012;44(6):999–1004.

Peters EM, Bateman ED. Ultramarathon running and upper respiratory tract infections-an epidemiological survey. S Afr Med J. 1983;64(15):582–4.

Nieman DC, Johanssen LM, Lee JW, Arabatzis K. Infectious episodes in runners before and after the Los Angeles Marathon. J Sports Med Phys Fit. 1990;30(3):316–28.

CAS   Google Scholar  

Furusawa K, Tajima F, Okawa H, Takahashi M, Ogata H. The incidence of post-race symptoms of upper respiratory tract infection in wheelchair marathon racers. Spinal Cord. 2007;45(7):513–7.

Moreira A, Mortatti AL, Arruda AF, Freitas CG, De Arruda M, Aoki MS. Salivary IgA response and upper respiratory tract infection symptoms during a 21-week competitive season in young soccer players. J Strength Cond Res. 2014;28(2):467–73.

Men accounted for about 75 percent of workers in protective service occupations in 2020. 2020. https://www.bls.gov/opub/ted/2021/men-accounted-for-about-75-percent-of-workers-in-protective-service-occupations-in-2020.htm . Accessed 7 Aug 2023.

Goodwin ML, Harris JE, Hernandez A, Gladden LB. Blood lactate measurements and analysis during exercise: a guide for clinicians. J Diabetes Sci Technol. 2007;1(4):558–69.

Navarro KM, Clark KA, Hardt DJ, Reid CE, Lahm PW, Domitrovich JW, et al. Wildland firefighter exposure to smoke and COVID-19: a new risk on the fire line. Sci Total Environ. 2021;760:144296.

Navarro KM, West MR, O’dell K, Sen P, Chen IC, Fischer EV, et al. Exposure to particulate matter and estimation of volatile organic compounds across wildland firefighter job tasks. Environ Sci Technol. 2021;55(17):11795–804.

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Acknowledgements

The authors thank Dr. Raghavendra Mirmira, University of Chicago, for insightful discussions. A portion of this research was performed at the Environmental Molecular Sciences Laboratory, a Department of Energy (DOE) Office of Science User Facility sponsored by the Biological and Environmental Research (BER) program under Contract No. DE-AC05-76RL01830.

This study was supported by the BRAVE Agile Investment from the PNNL.

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Ernesto S. Nakayasu, Marina A. Gritsenko, Young-Mo Kim, Jennifer E. Kyle, Kelly G. Stratton, Carrie D. Nicora, Yuqian Gao, Karl K. Weitz, Vanessa L. Paurus, Kent J. Bloodsworth & Lisa M. Bramer

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Contributions

ESN helped with the conceptualization of the project, led the data analysis and biological interpretations, and wrote the first draft of the manuscript. MAG contributed to the conceptualization of the project, sample collection and sample preparation, performed the ELISA assays, and contributed to the manuscript draft. YMK, VLP and NM performed the metabolomics analysis, and contributed with the manuscript draft. CDN, YG and KKW performed the proteomics analysis, and helped with the manuscript draft. JEK and KJB performed the lipidomics analysis and helped with the manuscript draft. LMB, KGS and DC performed the statistical analysis and helped with the manuscript draft. KGS, DC and LMB performed the multi-omics data integration and helped with the manuscript draft. KMN and KAC contributed to the biological interpretations and helped with the manuscript draft. KAA led the logistics of the project, and helped with the study design and project supervision. FM contributed to the project supervision, cohort recruitment and physiological aspects of the project. GT contributed to the conceptualization of the project, cohort recruitment and supervision of the project. JT and KEBJ led the project, obtained the funds, and contributed to biological interpretations and writing the manuscript. All authors read and approved the final manuscript.

Corresponding authors

Correspondence to Ernesto S. Nakayasu , Justin Teeguarden or Kristin E. Burnum-Johnson .

Ethics declarations

The study was conducted after approval from the Institutional Review Board of the Pacific Northwest National Laboratory (PNNL IRB #2019-17) and participants signed information consent in accordance with federal regulations.

Consent for publication

The consent signed by participants of the study included permission for publishing the research findings and was captured in accordance with federal regulations.

Competing interests

The authors declare that they have no competing interests.

Supplementary Information

Additional file 1:.

Table S1 Quantitative proteomics analysis of plasma, saliva, and urine. Plasma samples were immunodepleted for the top 14 most abundant proteins, digested with trypsin, labeled with tandem mass tags, and fractionated by high pH reverse phase chromatography before being analyzed by LC-MS/MS. Saliva and urine were digested with trypsin and analyzed by label-free LC-MS/MS. Proteins were considered significantly different with a P ≤ 0.05 by Student’s t -test (highlighted in green). Fold changes are highlighted in degrees of red (up-regulation) and blue (down-regulation). Table S2 Quantitative lipidomics analysis of plasma, saliva, and urine. Plasma, saliva, and urine extracted with chloroform: methanol: water and analyzed by LC-MS/MS in both positive and negative ionization modes. Lipids were considered significantly different with a P ≤ 0.05 by Student’s t -test (highlighted in green). Fold changes are highlighted in degrees of red (up-regulation) and blue (down-regulation). “_A”, “_B” or “_C” denotes different chromatographically resolved isomers. Table S3 Metabolomics analysis of plasma, saliva, and urine. Plasma, saliva, and urine extracted with methanol, derivatized and analyzed by GC-MS. Metabolites were considered significantly different with a P ≤ 0.05 by Student’s t -test (highlighted in green). Fold changes are highlighted in degrees of red (up-regulation) and blue (down-regulation). Table S4 Quantitative plasma proteomics analysis. Plasma samples were immunodepleted for the top 14 most abundant proteins, digested with trypsin, labeled with tandem mass tags, and fractionated by high pH reverse phase chromatography before being analyzed by LC-MS/MS. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S5 Quantitative plasma metabolomics analysis. Plasma samples were extracted with methanol, derivatized with N -methyl- N -(trimethylsilyl)trifluoroacetamide and analyzed by GC-MS. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S6 Quantitative plasma lipidomics analysis. Plasma samples were extracted with MPLEx and analyzed by LC-MS/MS in both positive and negative ionization modes. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S7 Quantitative urine proteomics analysis. Urine samples were digested with trypsin and analyzed by LC-MS/MS. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S8 Quantitative urine metabolomics analysis. Urine samples were extracted with methanol, derivatized with N -methyl- N -(trimethylsilyl)trifluoroacetamide and analyzed by GC-MS. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S9 Quantitative urine lipidomics analysis. Urine samples were extracted with MPLEx and analyzed by LC-MS/MS in both positive and negative ionization modes. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S10 Quantitative saliva proteomics analysis. Saliva samples were digested with trypsin and analyzed by LC-MS/MS. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S11 Quantitative saliva metabolomics analysis. Saliva samples were extracted with methanol, derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide and analyzed by GC-MS. Significance was calculated with Student’s t -test. Values represent normalized intensities. Table S12 Quantitative saliva lipidomics analysis. Saliva samples were extracted with MPLEx and analyzed by LC-MS/MS in both positive and negative ionization modes. Significance was calculated with Student’s t -test. Values represent normalized intensities.

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Nakayasu, E.S., Gritsenko, M.A., Kim, YM. et al. Elucidating regulatory processes of intense physical activity by multi-omics analysis. Military Med Res 10 , 48 (2023). https://doi.org/10.1186/s40779-023-00477-5

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Writing a Research Paper Conclusion | Step-by-Step Guide

Published on October 30, 2022 by Jack Caulfield . Revised on April 13, 2023.

• Restate the problem statement addressed in the paper
• Summarize your overall arguments or findings
• Suggest the key takeaways from your paper

The content of the conclusion varies depending on whether your paper presents the results of original empirical research or constructs an argument through engagement with sources .

Table of contents

Step 1: restate the problem, step 2: sum up the paper, step 3: discuss the implications, research paper conclusion examples, frequently asked questions about research paper conclusions.

The first task of your conclusion is to remind the reader of your research problem . You will have discussed this problem in depth throughout the body, but now the point is to zoom back out from the details to the bigger picture.

While you are restating a problem you’ve already introduced, you should avoid phrasing it identically to how it appeared in the introduction . Ideally, you’ll find a novel way to circle back to the problem from the more detailed ideas discussed in the body.

For example, an argumentative paper advocating new measures to reduce the environmental impact of agriculture might restate its problem as follows:

Meanwhile, an empirical paper studying the relationship of Instagram use with body image issues might present its problem like this:

“In conclusion …”

Avoid starting your conclusion with phrases like “In conclusion” or “To conclude,” as this can come across as too obvious and make your writing seem unsophisticated. The content and placement of your conclusion should make its function clear without the need for additional signposting.

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Having zoomed back in on the problem, it’s time to summarize how the body of the paper went about addressing it, and what conclusions this approach led to.

Depending on the nature of your research paper, this might mean restating your thesis and arguments, or summarizing your overall findings.

Argumentative paper: Restate your thesis and arguments

In an argumentative paper, you will have presented a thesis statement in your introduction, expressing the overall claim your paper argues for. In the conclusion, you should restate the thesis and show how it has been developed through the body of the paper.

Briefly summarize the key arguments made in the body, showing how each of them contributes to proving your thesis. You may also mention any counterarguments you addressed, emphasizing why your thesis holds up against them, particularly if your argument is a controversial one.

Don’t go into the details of your evidence or present new ideas; focus on outlining in broad strokes the argument you have made.

Empirical paper: Summarize your findings

In an empirical paper, this is the time to summarize your key findings. Don’t go into great detail here (you will have presented your in-depth results and discussion already), but do clearly express the answers to the research questions you investigated.

Describe your main findings, even if they weren’t necessarily the ones you expected or hoped for, and explain the overall conclusion they led you to.

Having summed up your key arguments or findings, the conclusion ends by considering the broader implications of your research. This means expressing the key takeaways, practical or theoretical, from your paper—often in the form of a call for action or suggestions for future research.

Argumentative paper: Strong closing statement

An argumentative paper generally ends with a strong closing statement. In the case of a practical argument, make a call for action: What actions do you think should be taken by the people or organizations concerned in response to your argument?

If your topic is more theoretical and unsuitable for a call for action, your closing statement should express the significance of your argument—for example, in proposing a new understanding of a topic or laying the groundwork for future research.

Empirical paper: Future research directions

In a more empirical paper, you can close by either making recommendations for practice (for example, in clinical or policy papers), or suggesting directions for future research.

Whatever the scope of your own research, there will always be room for further investigation of related topics, and you’ll often discover new questions and problems during the research process .

Finish your paper on a forward-looking note by suggesting how you or other researchers might build on this topic in the future and address any limitations of the current paper.

Full examples of research paper conclusions are shown in the tabs below: one for an argumentative paper, the other for an empirical paper.

• Argumentative paper
• Empirical paper

While the role of cattle in climate change is by now common knowledge, countries like the Netherlands continually fail to confront this issue with the urgency it deserves. The evidence is clear: To create a truly futureproof agricultural sector, Dutch farmers must be incentivized to transition from livestock farming to sustainable vegetable farming. As well as dramatically lowering emissions, plant-based agriculture, if approached in the right way, can produce more food with less land, providing opportunities for nature regeneration areas that will themselves contribute to climate targets. Although this approach would have economic ramifications, from a long-term perspective, it would represent a significant step towards a more sustainable and resilient national economy. Transitioning to sustainable vegetable farming will make the Netherlands greener and healthier, setting an example for other European governments. Farmers, policymakers, and consumers must focus on the future, not just on their own short-term interests, and work to implement this transition now.

As social media becomes increasingly central to young people’s everyday lives, it is important to understand how different platforms affect their developing self-conception. By testing the effect of daily Instagram use among teenage girls, this study established that highly visual social media does indeed have a significant effect on body image concerns, with a strong correlation between the amount of time spent on the platform and participants’ self-reported dissatisfaction with their appearance. However, the strength of this effect was moderated by pre-test self-esteem ratings: Participants with higher self-esteem were less likely to experience an increase in body image concerns after using Instagram. This suggests that, while Instagram does impact body image, it is also important to consider the wider social and psychological context in which this usage occurs: Teenagers who are already predisposed to self-esteem issues may be at greater risk of experiencing negative effects. Future research into Instagram and other highly visual social media should focus on establishing a clearer picture of how self-esteem and related constructs influence young people’s experiences of these platforms. Furthermore, while this experiment measured Instagram usage in terms of time spent on the platform, observational studies are required to gain more insight into different patterns of usage—to investigate, for instance, whether active posting is associated with different effects than passive consumption of social media content.

If you’re unsure about the conclusion, it can be helpful to ask a friend or fellow student to read your conclusion and summarize the main takeaways.

• Do they understand from your conclusion what your research was about?
• Are they able to summarize the implications of your findings?
• Can they answer your research question based on your conclusion?

You can also get an expert to proofread and feedback your paper with a paper editing service .

The conclusion of a research paper has several key elements you should make sure to include:

• A restatement of the research problem
• A summary of your key arguments and/or findings
• A short discussion of the implications of your research

No, it’s not appropriate to present new arguments or evidence in the conclusion . While you might be tempted to save a striking argument for last, research papers follow a more formal structure than this.

All your findings and arguments should be presented in the body of the text (more specifically in the results and discussion sections if you are following a scientific structure). The conclusion is meant to summarize and reflect on the evidence and arguments you have already presented, not introduce new ones.

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How to Write a Discussion Section | Tips & Examples

Published on 21 August 2022 by Shona McCombes . Revised on 25 October 2022.

The discussion section is where you delve into the meaning, importance, and relevance of your results .

It should focus on explaining and evaluating what you found, showing how it relates to your literature review , and making an argument in support of your overall conclusion . It should not be a second results section .

There are different ways to write this section, but you can focus your writing around these key elements:

• Summary: A brief recap of your key results
• Interpretations: What do your results mean?
• Implications: Why do your results matter?
• Limitations: What can’t your results tell us?
• Recommendations: Avenues for further studies or analyses

Table of contents

What not to include in your discussion section, step 1: summarise your key findings, step 2: give your interpretations, step 3: discuss the implications, step 4: acknowledge the limitations, step 5: share your recommendations, discussion section example.

There are a few common mistakes to avoid when writing the discussion section of your paper.

• Don’t introduce new results: You should only discuss the data that you have already reported in your results section .
• Don’t make inflated claims: Avoid overinterpretation and speculation that isn’t directly supported by your data.
• Don’t undermine your research: The discussion of limitations should aim to strengthen your credibility, not emphasise weaknesses or failures.

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Start this section by reiterating your research problem  and concisely summarising your major findings. Don’t just repeat all the data you have already reported – aim for a clear statement of the overall result that directly answers your main  research question . This should be no more than one paragraph.

Many students struggle with the differences between a discussion section and a results section . The crux of the matter is that your results sections should present your results, and your discussion section should subjectively evaluate them. Try not to blend elements of these two sections, in order to keep your paper sharp.

• The results indicate that …
• The study demonstrates a correlation between …
• This analysis supports the theory that …
• The data suggest  that …

The meaning of your results may seem obvious to you, but it’s important to spell out their significance for your reader, showing exactly how they answer your research question.

The form of your interpretations will depend on the type of research, but some typical approaches to interpreting the data include:

• Identifying correlations , patterns, and relationships among the data
• Discussing whether the results met your expectations or supported your hypotheses
• Contextualising your findings within previous research and theory
• Explaining unexpected results and evaluating their significance
• Considering possible alternative explanations and making an argument for your position

You can organise your discussion around key themes, hypotheses, or research questions, following the same structure as your results section. Alternatively, you can also begin by highlighting the most significant or unexpected results.

• In line with the hypothesis …
• Contrary to the hypothesised association …
• The results contradict the claims of Smith (2007) that …
• The results might suggest that x . However, based on the findings of similar studies, a more plausible explanation is x .

As well as giving your own interpretations, make sure to relate your results back to the scholarly work that you surveyed in the literature review . The discussion should show how your findings fit with existing knowledge, what new insights they contribute, and what consequences they have for theory or practice.

Ask yourself these questions:

• Do your results support or challenge existing theories? If they support existing theories, what new information do they contribute? If they challenge existing theories, why do you think that is?
• Are there any practical implications?

Your overall aim is to show the reader exactly what your research has contributed, and why they should care.

• These results build on existing evidence of …
• The results do not fit with the theory that …
• The experiment provides a new insight into the relationship between …
• These results should be taken into account when considering how to …
• The data contribute a clearer understanding of …
• While previous research has focused on  x , these results demonstrate that y .

Even the best research has its limitations. Acknowledging these is important to demonstrate your credibility. Limitations aren’t about listing your errors, but about providing an accurate picture of what can and cannot be concluded from your study.

Limitations might be due to your overall research design, specific methodological choices , or unanticipated obstacles that emerged during your research process.

Here are a few common possibilities:

• If your sample size was small or limited to a specific group of people, explain how generalisability is limited.
• If you encountered problems when gathering or analysing data, explain how these influenced the results.
• If there are potential confounding variables that you were unable to control, acknowledge the effect these may have had.

After noting the limitations, you can reiterate why the results are nonetheless valid for the purpose of answering your research question.

• The generalisability of the results is limited by …
• The reliability of these data is impacted by …
• Due to the lack of data on x , the results cannot confirm …
• The methodological choices were constrained by …
• It is beyond the scope of this study to …

Based on the discussion of your results, you can make recommendations for practical implementation or further research. Sometimes, the recommendations are saved for the conclusion .

Suggestions for further research can lead directly from the limitations. Don’t just state that more studies should be done – give concrete ideas for how future work can build on areas that your own research was unable to address.

• Further research is needed to establish …
• Future studies should take into account …
• Avenues for future research include …

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