Review Reports - Acute Effects of Intermittent High-Intensity Exercise on Cardiac Autonomic Regulation in Male Non-Elite Badminton Players: A Multi-Point Time Series Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript Title: Acute Effects of Intermittent High-Intensity Exercise on Cardiac Autonomic Regulation in Male Non-Elite Badminton Players: A Multi-Point Time Series Analysis

First of all, the reviewer would like to thank the authors for their work and efforts to improve knowledge in sports science.

The acute time-course effects of a sport-specific intermittent high-intensity badminton field test on heart rate variability (HRV) indices in male non-elite college players are examined in this study. This topic is important for training-load management in applied sport physiology, especially for recreational or amateur athletes who are underrepresented in the HRV literature. Theoretical strengths include the use of effect sizes and a multi-time-point design. However, the paper has several methodological, analytical, and reporting issues that need to be resolved before publication can be considered, despite its practical significance. Although the work needs significant improvement, it has the potential to be published.

Abstract

Line 15-16: The authors said

“until reaching fatigue (≥92% HRmax or RPE≥18).”

This means until exhaustion. Please change it until exhaustion.

Line 17: The authors said

“Stress index (SI)”

How was this expression measured? Please cite it

Line 35-41: The language used in this section is too sharp and direct. These expressions should be softened somewhat.

Introduction section

The introduction should be rewritten to include information for non-elite athletes, discuss sport-specific load protocols, and address multi-time-point recovery.

Line 76-77: Details should be provided.

Methods section

Line 109: Needle phobia?? Why was this prescribed? Is there an invasive procedure involved? If not, should it be removed?

It should be specified whether caffeine, alcohol, sleep, and exercise restrictions were checked.

Was hydration checked? If not, it should be added as a limitation.

Were the measurements taken under the same environmental conditions? This should be specified.

How was HRmax calculated? Was it an estimated formula or a measurement?

Respiratory rate was not checked. HF interpretation is therefore limited. This should be added as a limitation.

Results section

This section is well-designed and well-written.

Discussion section

Overall, the discussion is well-written and incorporates relevant literature.

Limitations

No control group, no respiratory control, small sample size, and only male, hydration, and sleep were not controlled. A new limitations section should be written in this context.

References

The authors should check the writing style of references according to the journal guidelines

Author Response

Dear Reviewer 1,

We sincerely appreciate your attention and comments regarding our manuscript titled "Acute Effects of Intermittent High-Intensity Exercise on Cardiac Autonomic Regulation in Male Non-Elite Badminton Players: A Multi-Point Time Series Analysis" (ID: healthcare-4184254). Your feedback is invaluable and has been instrumental in the revision and enhancement of our manuscript, while also providing significant guidance for our future research. The revised sections have been highlighted in red text throughout the manuscript. Additionally, to improve readability, we have engaged a professional English editing service to enhance the language, with these modifications indicated in blue text. Below is our point-by-point response to your comments. We look forward to your reply. The certificate of English editing is provided as follows.

Reviewer 1

Comment: First of all, the reviewer would like to thank the authors for their work and efforts to improve knowledge in sports science.

Responses:

We thank the reviewers for their comments and contributions.

Abstract

Comment: Line 15-16: The authors said

“until reaching fatigue (≥92% HRmax or RPE≥18).”
This means until exhaustion. Please change it until exhaustion.

Responses:

Thank you for your comments. We have completed the revisions. Furthermore, based on suggestions from another reviewer, we have simplified the abstract section.

Revisions: Line 16.

Participants completed 5 sets of high-intensity intermittent court tests until exhaustion

Comment: Line 17: The authors said

“Stress index (SI)”

How was this expression measured? Please cite it

Responses:

Thank you for your comments and suggestions. We have added the calculation formula for SI and relevant literature citations in the Methods section.

Revisions: Line 158-163.

The stress index (SI) was to calculated to assess sympathetic tone and reactivity based on heart rate variability [24]. The SI formula is SI=(AMo)*100 / (2Mo* MxDMn), where Mo is the mode, the most common RR interval during a study period; (AMo)x100 is the % of the number of mode values compared to all values; and MxDMn is the difference between the maximum and the minimum value of the RR intervals. A description of the HRV indicators is shown in Table 1 [25,26].

Comment: Line 35-41: The language used in this section is too sharp and direct. These expressions should be softened somewhat.

Responses:

Thank you for your comments. We have revised the text to adopt a more moderate expression.

Revisions: Line 35-44.

Conclusions: Following high-intensity exercise leading to peripheral fatigue, cardiac autonomic function demonstrates a “suppression-recovery” dynamic pattern: cardiac stress levels increase significantly within 15 minutes post-exercise, with decreased overall HRV regulatory capacity and strong inhibition of parasympathetic activity; HRV status may return to baseline levels after 24 hours. However, the frequency-domain indices of HRV showed no significant changes in response to the acute effects of high-intensity exercise.

Introduction section

Comment: The introduction should be rewritten to include information for non-elite athletes, discuss sport-specific load protocols, and address multi-time-point recovery.

Line 76-77: Details should be provided.

Responses:

Thank you for your comments. We have revised the expression and added literature citations to re-explain the physiological mechanisms of HRV. Additionally, in the final paragraph, we have highlighted that this paper includes information on non-elite athletes, discusses sport-specific loading protocols, and addresses the value of multi-time-point recovery analysis.

Revisions: Line 65-91.

Methods section

Comment: Line 109: Needle phobia?? Why was this prescribed? Is there an invasive procedure involved? If not, should it be removed

Responses:

Thank you for your careful reminder. We have removed "Needle phobia" as no invasive procedures were involved.

Revisions: Line 111-112.

Subjects were excluded if they had one of the following conditions: joint or muscle dysfunction, including severe back, neck, knee, and ankle pain;

Comment: It should be specified whether caffeine, alcohol, sleep, and exercise restrictions were checked.
Was hydration checked? If not, it should be added as a limitation.

Responses:

Thank you for your comments. Prior to the experiment, we had specific requirements regarding alcohol, sleep, and exercise restrictions; however, caffeine status was not recorded. Post-exercise, participants were provided with normal hydration without specific requirements or documentation. We have added relevant statements and included explanations regarding the potential effects of caffeine and hydration in the Limitations section.

Revisions: Line 119-123.

All participants were instructed to abstain from alcohol and other vigorous exercise for 3 days prior to the experiment until 48 hours after the exercise load, and to maintain normal sleep patterns without staying up late. Hydration was provided after the exercise test, but there was no specific requirement to record fluid intake.

Revisions: Line 339-354.

Although the present findings support integrating time-domain HRV (RMSSD, SDNN) and stress index into training monitoring for recreational badminton players, several methodological and physiological constraints warrant cautious interpretation. First, breathing patterns can significantly interfere with frequency-domain HRV indices [31]; although time-domain indices are less affected by respiration, uncontrolled breathing patterns may still constitute an influencing factor. Second, sleep quality is a critical but difficult-to-control recovery regulatory factor; despite requiring participants to maintain habitual sleep schedules, unmonitored sleep structure and quality may lead to inter-individual differences in HRV recovery dynamics. Third, the single-arm uncontrolled experimental design limits causal inference; our findings are also only applicable to young male amateur athletes. Fourth, participants were provided with hydration post-exercise, but the amount of fluid intake was not specifically recorded; although all participants were healthy young adults, the hydration status may also influence the results. Future multi-time-point studies should incorporate assessments of respiratory rate, hydration status, and subjective sleep quality to control for the effects of these factors on post-exercise autonomic recovery.

Comment: Were the measurements taken under the same environmental conditions? This should be specified.

Responses:

We have added clarification that the 24-hour and 48-hour tests were conducted under identical environmental conditions.

Revisions: Line 155-157.

The measurements at 24 and 48 hours post-exercise were scheduled at the same time points and under the same environmental conditions.

Comment: How was HRmax calculated? Was it an estimated formula or a measurement?

Responses:

We have added the formula and citations.

Revisions: Line 144-147.

(1) cannot run or stop by participants themselves or (2) HR of 92% of HRmax (calculated using the formula: 220 - 0.78 × age) [21,22], or ③ RPE ≥18 score [23].

Comment: Respiratory rate was not checked. HF interpretation is therefore limited. This should be added as a limitation.

Responses:

Thank you for pointing this out. Since our subjects were healthy young amateur athletes, respiratory frequency increased significantly during high-intensity exercise, but returned to normal levels at 24 and 48 hours post-exercise; therefore, we did not specify requirements for respiratory frequency. The literature has reported the effects of respiratory frequency on HRV, and we have accordingly added this explanation in the Limitations section.

Revisions: Line 341-344.

First, breathing patterns can significantly interfere with frequency-domain HRV indices [31]; although time-domain indices are less affected by respiration, uncontrolled breathing patterns may still constitute an influencing factor.

Results section

Comment: This section is well-designed and well-written.

Responses: We appreciate your recognition of our work.

Discussion section

Comment: Overall, the discussion is well-written and incorporates relevant literature.

Responses:

We appreciate your recognition of our work. Based on the comments from other reviewers, we have revised the discussion section accordingly.

Limitations

Comment: No control group, no respiratory control, small sample size, and only male, hydration, and sleep were not controlled. A new limitations section should be written in this context.

Responses:

Thank you for your suggestions. Following your recommendations, we have rewritten the Limitations section. We have re-explained the potential impacts of the single-arm design without control group, small sample size, male-only participants, lack of respiratory control, and uncontrolled hydration and sleep on the results.

Revisions: Line 337-354.

References

Comment: The authors should check the writing style of references according to the journal guidelines

Responses:

We have revised the manuscript by removing duplicate references and adding new citations.

Finally, we would like to thank you again for your constructive comments and valuable critiques, as well as for taking the time to analyze this manuscript. We are deeply grateful for your assistance and patience.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors clearly presented the impact of intense cardiac exercise on badminton players. This study is of interest to the readers in the health care community. My minor comments to the authors are attached.

Comments to the author:

1. From Figure 3b, it is observed that the SI decreases during post-exercise, and why does the stress index increase to 41.68 for post-exercise 48 hours?

2. Why does the LF/HF ratio decrease to a lower value than in the pre-exercise condition?

3. Include a paragraph in the discussion highlighting the challenges from the present study.

4. Rewrite the first paragraph in the discussion as: In this section, the interpreted results are discussed from the perspective of previous studies. Future research directions are also highlighted.

Author Response

Dear Reviewer 2,

Comment: The authors clearly presented the impact of intense cardiac exercise on badminton players. This study is of interest to the readers in the health care community. My minor comments to the authors are attached.

Comments to the author:

1. Comment: From Figure 3b, it is observed that the SI decreases during post-exercise, and why does the stress index increase to 41.68 for post-exercise 48 hours?

Responses:

We thank you for this careful observation. Indeed, consistent with the data from Figure 3b and Table 3, the SI increased significantly immediately post-exercise and at 15 minutes (from 36.92 to 45.16 and 46.76), decreased to 36.08 at 24 hours, but then increased again to 41.68 at 48 hours. We have verified the data and confirmed no errors were present. Statistically, the SI value at 48 hours showed no significant differences from the other four time points (our post-hoc test indicates that the 48-hour data in Table 3 is not marked with letters a-d). The potential cause may be measurement fluctuations due to the small sample size, despite the lack of statistical significance. However, other factors cannot be ruled out, which requires further explanation and validation. We have added relevant statements in the Results section.

Revisions: Line 216-220.

At 24 and 48 hours post-exercise, values were 36.08 and 41.68 respectively, showing no significant differences (P>0.05). Although no statistical significance was observed, the SI value at 48 hours post-exercise increased to 41.68.

2. Comment: Why does the LF/HF ratio decrease to a lower value than in the pre-exercise condition?

Responses:

Thank you for this careful observation. Similar to the previous issue, Table 3 shows that the three frequency-domain parameters (LF, HF, and LF/HF) exhibited no statistically significant differences across the five time points (both trend analysis and pairwise post-hoc tests showed all P-values > 0.05). The LF/HF ratio at 48 hours was 1.15, lower than the pre-exercise value of 1.21, primarily due to a greater reduction in LF, though neither reached statistical significance. We suggest that this may be attributed to measurement fluctuations caused by the small sample size. Additionally, our experiment indicates that frequency-domain HRV analysis is not sensitive following high-intensity exercise. Furthermore, we have added literature citations and included a paragraph in the Introduction stating that the physiological interpretation of LF/HF requires more cautious consideration, as its validity as a sympathetic-parasympathetic marker remains under debate.

Revisions: Line 64-66.

3. Comment: Include a paragraph in the discussion highlighting the challenges from the present study.

Responses:

We thank the reviewer for this suggestion. We have added a paragraph addressing the challenges.

Revisions: Line 305-315.

Recent studies have demonstrated that immediately post-exercise, SDNN, RMSSD, HF, and LF values significantly decreased compared to pre-exercise levels [9,10]. The HRV response to exercise modalities was similar between high-intensity exercise and moderate-intensity exercise, suggesting that this similarity may be advantageous for exercise prescription and programming from an autonomic function perspective [9]. However, these previous studies were based on small sample sizes, which may introduce random measurement errors. Our present analysis, based on 25 subjects, faces similar limitations. Different HRV measurement methodologies necessitate cautious interpretation of results [16]. The inconsistent reports regarding LF, HF, and LF/HF responses following high-intensity exercise, while requiring careful physiological interpretation, present challenges for future research.

4. Comment: Rewrite the first paragraph in the discussion as: In this section, the interpreted results are discussed from the perspective of previous studies. Future research directions are also highlighted.

Responses:

Following your recommendation, we have rewritten the first paragraph of the discussion section with additional elaboration.

Revisions: Line 278-283.

We interpret and discuss the findings of this study in conjunction with previous research. The results indicate that sport-specific high-intensity interval exercise leads to significant parasympathetic withdrawal in non-professional badminton players, with recovery dynamics that differ from those reported in professional athletes. The frequency-domain indices were insensitive to these acute changes, a phenomenon that raises important considerations for optimal HRV monitoring protocols in amateur sports settings.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Abstract

The abstract is overly dense and numerically overloaded; consider simplifying statistical reporting.
Some conclusions are overstated (e.g., “frequency-domain analysis is insensitive”) without sufficient nuance.
The practical recommendation appears stronger than warranted by the design.

Introduction

The rationale is generally well developed but somewhat repetitive.
The research gap should be more clearly articulated in one concise paragraph.
More recent consensus statements on HRV interpretation in exercise physiology should be included.
The physiological explanation of LF/HF requires more caution, given ongoing debate regarding its validity as a sympathovagal marker.

Methods

Single-arm design without control condition limits causal inference.
No comparison with other exercise intensities or a control day (rest condition).
External validity is limited to young male collegiate recreational players.

Exercise Protocol

The fatigue criteria (≥92% HRmax OR RPE ≥18 OR voluntary cessation) introduce heterogeneity in termination criteria.
It is unclear whether all participants reached comparable physiological stress levels.
The protocol duration (“15-minute field test”) appears inconsistent with fatigue-based termination.

HRV Measurement

5-minute recordings are appropriate; however:

Breathing rate was not controlled or reported (major limitation for HF interpretation).
Time of day standardization is not clearly described.
Caffeine, hydration, and prior training control procedures are insufficiently detailed.

The “Stress Index” algorithm requires clearer description and validation reference.

Discussion

The comparison with elite cohorts is interesting but indirect (no direct comparator group).
Statements about “insensitivity” of frequency-domain HRV are too definitive.
LF/HF interpretation should acknowledge methodological controversies.
Baroreflex sensitivity is mentioned in conclusions but not directly measured.
Recovery conclusion (“24 hours sufficient”) may be overstated without longer follow-up.
Practical recommendations are promising but somewhat speculative.

Conclusions

Conclusions should be more conservative.
Replace “HRV frequency-domain analysis is insensitive” with more cautious wording.
Avoid implying mechanistic explanations (e.g., baroreflex restoration) not directly measured.
Emphasize that findings apply specifically to young male recreational players.

Author Response

Dear Reviewer 3,

Abstract

1. Comment: The abstract is overly dense and numerically overloaded; consider simplifying statistical reporting.

Responses:

Thank you for your comments. We have simplified the abstract according to your suggestions.

Revisions: Line 12-44.

2. Comment: Some conclusions are overstated (e.g., “frequency-domain analysis is insensitive”) without sufficient nuance.

The practical recommendation appears stronger than warranted by the design.

Responses:

Thank you for your comments. We have revised the conclusion based on your suggestions.

Revisions: Line 12-44.

Introduction

3. Comment: The rationale is generally well developed but somewhat repetitive.

The research gap should be more clearly articulated in one concise paragraph.

More recent consensus statements on HRV interpretation in exercise physiology should be included.

Responses:

Thank you for your comments. We have revised the introduction section according to your suggestions, adding reference citations and consensus statements regarding HRV interpretation.

Revisions: Line 64-91.

However, LF/HF has traditionally been used to evaluate sympathovagal balance and the autonomic nervous response to physical stress, although its validity as a marker of sympathetic-parasympathetic activity remains controversial [7]. The prevailing view on post-exercise changes in cardiac autonomic function is that the immediate post-exercise reduction in HRV is a direct and primary manifestation of cardiac vagal tone inhibition [8-11]. However, reports on the sensitivity of HRV time-domain and frequency-domain analyses in capturing cardiac autonomic function changes following high-intensity exercise are inconsistent. Two studies reported significant reductions in both time-domain and frequency-domain HRV parameters immediately after acute exercise compared with pre-exercise levels [9,10], while two other studies indicated that frequency-domain parameters were unaffected following moderate-intensity continuous training or high-intensity interval exercise [12,13]. Additionally, research has shown that HRV responses to high-intensity exercise differ between populations (e.g., elite vs. recreational athletes) [14,15]. Recent consensus statements underscore that this variability arises from the context-dependent nature of autonomic recovery, influenced by exercise modality, measurement standardization, and individual autonomic responsiveness, rather than inherent ambiguity in physiological mechanisms [16,17]. For instance, compared with elite athletes, recreational players exhibit distinct autonomic recovery dynamics, but their HRV responses following sport-specific exercise loads lack in-depth investigation, particularly regarding HRV recovery patterns in amateur players [18,19].

This study aimed to investigate the acute HRV response characteristics of male recreational badminton players following a sport-specific high-intensity intermittent court test (FT) leading to peripheral fatigue. This study investigated sport-specific loading protocols and analyzed post-exercise HRV recovery at multiple time points in non-Elite athletes to elucidate the dynamic changes and recovery trajectories of the autonomic nervous system. The findings will provide evidence for developing personalized training strategies for recreational players, contributing to optimized training load management and monitoring of overtraining risks.

4. Comment: The physiological explanation of LF/HF requires more caution, given ongoing debate regarding its validity as a sympathovagal marker.

Responses:

we have added literature citations and included a paragraph in the Introduction stating that the physiological interpretation of LF/HF requires more cautious consideration, as its validity as a sympathetic-parasympathetic marker remains under debate.

Revisions: Line 64-66.

Methods

5. Comment: Single-arm design without control condition limits causal inference.

Responses:

Thank you for your comments. The rationale for considering a single-arm design is that, under natural conditions without external environmental changes, HRV in healthy young adults theoretically should not change significantly. Therefore, given our limited sample size, we chose a single-arm design without control group, which indeed limits causal inference. We have added this explanation in the Limitations section of the Discussion.

Revisions: Line 347-349.

Third, the single-arm uncontrolled experimental design limits causal inference; our findings are also only applicable to young male amateur athletes.

6. Comment: No comparison with other exercise intensities or a control day (rest condition).

Responses:

Thank you for your comments. Previous studies have compared high-intensity exercise and moderate-intensity exercise, showing similar HRV responses and suggesting that this similarity may be beneficial for exercise prescription and programming. Our primary objective was not to compare different exercise intensities and modalities, and our sample size was limited. For non-elite athletes, dynamic HRV monitoring following high-intensity loading is more valuable, so we selected high-intensity exercise. The testing times and environments at 24 hours and 48 hours were identical, and we have added relevant clarification.

Revisions: Line 155-157.

The measurements at 24 and 48 hours post-exercise were scheduled at the same time points and under the same environmental conditions.

Revisions: Line 305-315.

7. Comment: External validity is limited to young male collegiate recreational players.

Responses:

Thank you for your comments. Indeed, the external validity of our study is limited to young male university recreational athletes. Therefore, we have also added this limitation statement.

Revisions: Line 337-354.

Exercise Protocol

8. Comment: The fatigue criteria (≥92% HRmax OR RPE ≥18 OR voluntary cessation) introduce heterogeneity in termination criteria.

It is unclear whether all participants reached comparable physiological stress levels.

Responses:

Thank you for your careful comments. Indeed, heterogeneity was introduced in the termination criteria based on individualized physiological differences. During testing, both heart rate and RPE were used simultaneously, and RPE was reported in the first paragraph of the Results (increased from 6 to 18.72 ± 1.31). Because RPE is a relative assessment, it allows most participants with different fitness levels to achieve similar physiological stress levels. Our method involved displaying a prominent RPE rating chart on the badminton court, with different colors and values representing different fatigue levels, facilitating participants' self-assessment and reporting, as shown in the figure below.

9. Comment: The protocol duration (“15-minute field test”) appears inconsistent with fatigue-based termination.

Responses:

Thank you for your careful review. Our entire testing protocol lasted approximately 15 minutes, including five sets of interval exercises.

10. Comment: 5-minute recordings are appropriate; however:

Breathing rate was not controlled or reported (major limitation for HF interpretation).

Responses:

Revisions: Line 341-344.

11. Comment: Time of day standardization is not clearly described.

Responses:

Thank you for your comments. Tests at 24 hours and 48 hours post-exercise were conducted at the same time points, and we have added relevant descriptions.

Revisions: Line 155-157.

The measurements at 24 and 48 hours post-exercise were scheduled at the same time points and under the same environmental conditions.

12. Comment: Caffeine, hydration, and prior training control procedures are insufficiently detailed.

Responses:

Thank you for your comments. We required participants to avoid vigorous exercise for 3 days before the experiment, and this statement has been added. However, we did not record caffeine intake. Post-exercise hydration was provided normally, but we did not record the amount of fluid intake. Therefore, we have also added this limitation statement.

Revisions: Line 118-122.

Revisions: Line339-354.

13. Comment: The “Stress Index” algorithm requires clearer description and validation reference.

Responses:

Thank you for your comments and suggestions. We have added the calculation formula for SI and relevant literature citations in the Methods section.

Revisions: Line 158-163.

Discussion

14. Comment: The comparison with elite cohorts is interesting but indirect (no direct comparator group).

Responses:

Thank you for your comments. Indeed, the comparison with elite cohorts was indirect, and we did not conduct statistical analysis. Therefore, this was simply discussed in the Discussion section and is not presented as our research findings and conclusions.

15. Comment: Statements about “insensitivity” of frequency-domain HRV are too definitive.

Responses:

Thank you for your comments. We have revised the expression.

Revisions: Line 64-66.

16. Comment: LF/HF interpretation should acknowledge methodological controversies.

Responses:

We have added relevant explanations and citations.

Revisions: Line 297-301.

LF/HF interpretation requires methodological caution given ongoing controversies regarding its validity as a sympathovagal balance marker [7]. The lack of significant changes in frequency-domain parameters in this study, —despite clear parasympathetic withdrawal evidenced by RMSSD, —reflects the known limitations of spectral analysis during non-stationary post-exercise recovery [6].

17. Comment: Baroreflex sensitivity is mentioned in conclusions but not directly measured.

Responses:

Thank you for your comments. We have revised the conclusion, removing statements about non-direct measurements.

Revisions: Line 64-66.

18. Comment: Recovery conclusion (“24 hours sufficient”) may be overstated without longer follow-up.
Practical recommendations are promising but somewhat speculative.

Responses:

Thank you for your comments. We have revised the conclusion, removing the statement that "24 hours is sufficient."

Revisions: Line 64-66.

19.Conclusions

Comment: Conclusions should be more conservative.

Replace “HRV frequency-domain analysis is insensitive” with more cautious wording.

Avoid implying mechanistic explanations (e.g., baroreflex restoration) not directly measured.

Emphasize that findings apply specifically to young male recreational players.

Responses:

Thank you for your comments and suggestions. We have revised the conclusion according to the reviewer's requirements and suggestions. Additionally, we have emphasized in the Limitations section that the research findings apply to young male recreational players.

Revisions: Line 356-361.

Following high-intensity exercise leading to peripheral fatigue, cardiac autonomic function demonstrates a “suppression-recovery” dynamic pattern: cardiac stress levels increase significantly within 15 minutes post-exercise, with decreased overall HRV regulatory capacity and strong inhibition of parasympathetic activity; HRV status may return to baseline levels after 24 hours. However, the frequency-domain indices of HRV showed no significant changes in response to the acute effects of high-intensity exercise.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors