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The final version is already fit to be published on PeerJ. However, I advise you to read thoroughly before publication when you receive the proofread manuscript. Good luck.
[# PeerJ Staff Note - this decision was reviewed and approved by Mike Climstein, a PeerJ Section Editor covering this Section #]
The second reviewer still suggests several points to be revised. Please read it carefully and revise accordingly. I will make my decision after I receive your revision.
**PeerJ Staff Note**: Please ensure that all review, editorial, and staff comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
"parasympathetic" vs. "vagal" has been standardized per Reviewer feedback, which strengthens clarity.
Ensure all figures are high resolution (≥300 dpi if submitted as images).
Current stated that the "Participants were rescheduled if menstruating at the time of testing."
This excludes active menstruation, but does NOT control for cycle phase in the remaining female participants. Either (a) document cycle phase at time of assessment in Methods section, or (b) prominently feature cycle phase as unmeasured confound in Limitations section
Address whether VO₂max measurement adds clinical value beyond simple PA assessment in clinical settings.
Thank you for your submission.
We have received comments back from Reviewer 1 and Reviewer 2, which can be seen below.
Reviewers request clearer, more concise writing, consistent terminology, consideration of menstrual cycle effects on HRV, inclusion of effect size in Table 1 and corrections to the p-value in the legend of Figure 1.
Minor revisions are required to meet publication standards. We invite you to submit a minor revision, ensuring that you carefully respond to all of the reviewers comments and provide a detailed, point-by-point rebuttal.
**PeerJ Staff Note:** Please ensure that all review, editorial, and staff comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
**Language Note:** When preparing your next revision, please ensure that your manuscript is reviewed either by a colleague who is proficient in English and familiar with the subject matter, or by a professional editing service. PeerJ offers language editing services; if you are interested, you may contact us at [email protected] for pricing details. Kindly include your manuscript number and
This study addresses an important gap in understanding autonomic function in overweight/obese college students. The comprehensive examination of PA intensity, body composition, and sex-specific HRV patterns is valuable. However, minor revisions would strengthen the manuscript's rigor and clarity
1. The introduction and abstract contain substantial repetition. Consolidate for clarity.
2. Consistently use "parasympathetic" vs. "vagal"—terms are used interchangeably without a clear distinction.
3. Menstrual cycle status in female participants could influence HRV. Was this assessed or discussed
No comments
Table 1: Provide effect sizes (e.g., Cohen's d) for between-group comparisons, not just p-values.
Nil
No comment
No comments
No comment
Figure 1 legend
Significance levels: *P < 0.05; **P < 0.01; *P < 0.001; NS = not significant (P > 0.05).
<0.001 Probably require three ***
**PeerJ Staff Note:** Please ensure that all review, editorial, and staff comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
**PeerJ Staff Note:** PeerJ's policy is that any additional references suggested during peer review should only be included if the authors find them relevant and useful.
**Language Note:** When preparing your next revision, please ensure that your manuscript is reviewed either by a colleague who is proficient in English and familiar with the subject matter, or by a professional editing service. PeerJ offers language editing services; if you are interested, you may contact us at [email protected] for pricing details. Kindly include your manuscript number and title in your inquiry. – PeerJ Staff
Strengths
I appreciate the authors for addressing an important public health issue by assessing heart rate variability (HRV) in overweight and obese college students. The manuscript demonstrates a better understanding of the physiological mechanisms linking physical activity, body composition, and autonomic nervous system function. The study design appropriately uses validated instruments (IPAQ-SF, Kubios HRV software) and follows ethical guidelines with proper institutional approval.
Areas for Improvement
1. Language and Grammar Issues (Critical) The English language needs significant improvement to ensure clarity for an international audience. Specific examples requiring revision include:
• Line 23: "To investigate how physical activity intensity and body composition independently influence heart rate variability" - should specify "examine" rather than "investigate how"
• Line 77: "All participants provided voluntary written informed consent" – can be rephrased as "All participants provided written informed consent voluntarily"
• Lines 121-122: "Inter-group differences of HRV indices were analyzed with the Kruskal-Wallis H test, followed by post hoc analyses" - needs clarification of which post hoc test was used
• Line 128: The sentence structure regarding variable selection is confusing and should be restructured for clarity
2. Literature Context and Knowledge Gap (Major) The introduction needs substantial expansion, particularly lines 57-66. While the authors mention that "the precise effects and dose-response relationships of varying PA intensities... require further investigation," they should:
• Provide more specific evidence of the knowledge gap in overweight/obese college populations specifically
• Better distinguish how their study differs from existing research
• Include more recent systematic reviews or meta-analyses on HRV and physical activity in this population
3. Professional Article Structure Issues
• The "Study Strengths and Limitations" section appears twice (lines 342-363); change it
• Figure legends need more descriptive detail, particularly Figure 3, which lacks sufficient explanation of the correlation coefficients and their interpretation
Strengths
The research question is well-defined and relevant to current public health concerns. The sample size calculation is appropriate (n=157 calculated, n=184 recruited), and the study meets ethical standards with proper institutional approval.
Areas for Improvement
1. Methodological Concerns (Major)
• The use of IPAQ-SF for physical activity assessment introduces significant recall bias, as acknowledged by the authors. However, they should discuss how this limitation specifically affects their conclusions
• The Astrand-Rhyming indirect test for VO2max assessment may not be optimal for obese individuals. The authors should justify the basis of choosing this and discuss potential accuracy limitations
• The 5-minute HRV recording, while standard, may not capture full autonomic variability in this population, and adequate rest was ensured through any history mentioning it.
2. Statistical Analysis Clarity (Moderate)
• Lines 128-130: The description of variable selection using AIC needs a clearer explanation
• The authors should specify which post hoc tests were used after Kruskal-Wallis testing
• Multicollinearity assessment (VIF < 5) is mentioned, but results are not reported
Strengths
The statistical approach using both correlation and multiple regression analysis is appropriate. The finding that moderate-to-high intensity physical activity improves HRV in this population is clinically relevant and supported by the data.
Critical Issues
1. Statistical Reporting (Major)
• The regression models explain only 5.2% to 14.7% of HRV variation, indicating substantial unmeasured confounding. The authors acknowledge this, but should discuss specific potential confounders and how they might affect interpretation
• Gender differences are reported, but the interaction between gender and physical activity on HRV outcomes is not explained
• The authors should report confidence intervals for all regression coefficients, not just beta values and p-values
2. Interpretation and Causality (Major)
• As a cross-sectional study, the authors appropriately acknowledge limitations regarding causality, but their conclusions sometimes imply causal relationships (e.g., "Physical activity enhances HRV")
• The finding that VO2max doesn't independently predict HRV when PA is included needs better interpretation
3. Clinical Significance (Moderate)
• While statistical significance is demonstrated, the clinical significance of the observed changes in HRV parameters should be discussed
• The authors should compare their effect sizes to established minimal clinically important differences in HRV parameters
1. Language and Clarity: The manuscript requires professional English editing before publication. The current language barriers significantly impact comprehension and scientific communication.
2. Statistical Reporting: Confidence intervals, effect sizes, and clinical significance interpretations need to be added throughout. The low R² values require more discussion of potential confounders.
Minor Issues
• Table 1 formatting could be improved with consistent decimal places
• Figure 4 legend should specify what the error bars represent
• References formatting needs consistency (some journal names are abbreviated, others are not)
1. The authors have addressed a very relevant topic, i.e., the impact of physical activity levels & body composition on HRV in OW/OB college students. It is a cross-sectional study where 184 students were enrolled.
2. Figure legends should have a full explanation of abbreviations and sufficient information to enable the reader to understand the figure without resorting to the text. The number of participants (n) should be mentioned for clarity of the figures.
3. There is no mention of VC (I believe “vital capacity”) in the methodology section, but it is mentioned in figures 1 & 3.
4. The description of “heart functional capacity” should be provided in the methodology section as well as in Figure 1.
5. The note provided for Figure 1 mentions that “it presents body composition indicators for the low, moderate, and high physical activity groups,” whereas the graphs included show parameters related to cardiorespiratory fitness.
6. In Figure 2, the values for the LF/HF ratio should be cross-checked (much higher values are mentioned) as the normal range documented in literature varies, but could be from 1.1 to 1.6, with a mean of 2.8
a. (Nunan D, Sandercock GRH, Brodie DA. A quantitative systematic review of normal values for short-term heart rate variability in healthy adults. Pacing Clin Electrophysiol (2010) 33:1407–17. 10.1111/j.1540-8159.2010.02841.x)
b. Munoz, M. L., van Roon, A., Riese, H., Thio, C., Oostenbroek, E., Westrik, I., de Geus, E. J., Gansevoort, R., Lefrandt, J., Nolte, I. M., & Snieder, H. (2015). Validity of (Ultra-)Short Recordings for Heart Rate Variability Measurements. PloS one, 10(9), e0138921. https://doi.org/10.1371/journal.pone.0138921
1. The authors have clearly stated the gap in knowledge and have nicely mentioned the rationale of the study while linking it with the importance of the investigation
2. In the methodology section, clarification is required regarding the categorization of overweight and obesity. The authors have used a cutoff point of 24kg/m2, whereas WHO WHO-recommended overweight category is from 25 kg/m2 to 29.9, and obesity is from 30 kg/m2 onwards. The limits for the Asian population are different (overweight 23-27.99 and obese 28 and above).
a. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight#:~:text=overweight%20is%20a%20BMI%20greater,than%20or%20equal%20to%2030
b. https://www.researchgate.net/publication/296026141_An_Epidemiological_Study_of_Overweight_and_Obesity_Among_Women_in_an_Urban_Area_of_North_India/figures?lo=1
3. Probably because of the confusion, there is overlap in OW & OB groups in the sense that some subjects (n=5 or 6 ) with BMI in the range of 28 to 28.4 are included in OB, whereas some subjects (n=3) with BMI 28.4 to 29.9 are included in the OW group. Two subjects are pathologically obese (Class III obesity and their data could affect the results in an unwanted way.
4. The calculation of physical activity levels and METS needs a little more explanation for the convenience of easy understanding for the reader
1. Age, Gender, and BMI are known to affect the values of HRV. Therefore, it is advised that the analysis should take care of these factors that could affect the interpretation of results.
a. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation. 1996 Mar 1;93(5):1043-65. PMID: 8598068).
b. Shaffer, F., & Ginsberg, J. P. (2017). An Overview of Heart Rate Variability Metrics and Norms. Frontiers in public health, 5, 258. https://doi.org/10.3389/fpubh.2017.00258
2. In the section on data and statistical analysis, it is mentioned that non-normally distributed data were log-transformed. It should also mention which variables were found to be not normally distributed and were log-transformed. (Figure 2 shows HRV data that is not log transformed, whereas Figure 4 shows that the data was log transformed). Looking at the Excel file, the HRV data seems to be non-normally distributed.
3. For HRV parameters discussion, it is always advisable to mention the respiratory rate during the recording of the ECG for HRV analysis. Shifts in respiratory rate and volume can markedly affect HRV indices.
4. There are some concerns about the actual data as given in the Excel file.
a. Some values of RMSSD in the data file are too small and force a person to think whether this is correct or not (2 ms or 3 ms).
b. At places, the heart rate and IBI (inter-beat intervals) do not correspond, though they are reciprocal. With an HR of 69, it is not possible to have a RR interval of 754. HR should be around 79bpm.
c. The values of the LF/HF ratio are too large. I am not sure whether the output of the software Kubios is responsible for this, or if there is some other problem.
d. Data should be reviewed and cross-checked.
1. As it is a cross-sectional study, the authors may not use words such as “improved”, “enhanced” when comparing the mild, medium, and heavy physical activity groups. Improvement or enhancement may be seen in longitudinal studies when one takes repeated measurements. The OW/OB college students performing moderate to vigorous physical activity exhibited higher values of HRV indices indicative of better autonomic control.
2. The conclusions should include statements based on the present piece of research work. The facts that are already documented should not be highlighted in the conclusions. E.g., Females are documented to have higher HRV indices, which does not necessarily mean that they have better outcomes in relation to autonomic activity/control. They are physiologically different, and one of the observed differences is that they have relatively higher values of HRV indices. It would suffice to say that the pattern of higher HRV indices was also observed in the OW/OB female college students.
3. There are some missing pieces in the methodology, results, and figures. Discussion may be improved by emphasizing the results of the study and avoiding jumping to conclusions on the basis of limited data, which has a lot of variance.
4. The claim that the medium physical activity group and high physical activity group did not differ in certain respects should be presented with a milder emphasis because of the following reasons:
a. The number of participants in the high activity group is far less (n=21) than the medium activity (n=76) and low physical activity (n=87). A non-significant result for HRV parameters could be a Type II error, especially with unequal sample sizes.
b. As there is a lot of variability in data, this could also lead to nonsignificant differences between medium and high physical activity groups.
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