The Effects of the Leg Position on the Nordic Hamstring Exercise Eccentric Force: A Randomized Cross-Over Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

Thanks for your submission. Sadly at this stage I cannot endorse this effort for publication as I have strong objections with the design, stats, and the info that is presented. 

I suggest you attempt to write it again from the start, using my feedback for having better clarity and acceptance. 

For example, you manually hold the tibia in proper position, which led to error in the measurement.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Minor syntax and grammar issues

Author Response

Dear Reviewer,

Thank you for your extensive review of our manuscript. We truly appreciate your feedback and have made several revisions based on your suggestions. However, some points require further clarification.

For the Abstract, we incorporated many of your comments to improve clarity and detail. However, due to the journal's strict 200-word limit, we were unable to include all suggested changes.

In the Introduction section, you pointed out several areas for improvement. Our introduction aimed to explain the importance of hamstring strengthening, methods for achieving this (focusing on eccentric strength and its advantages), and one of the most common eccentric exercises for the hamstring (i.e., Nordic hamstrings). We also discussed the anatomy and function of the hamstrings, the influence of tibial positioning on their activation, and the justification for our study. While we understand your preference for a different approach, we believe our introduction is coherent and relevant to the study. For instance, we did not delve into electromyography in the introduction as it serves as a methodological tool rather than a core background topic. Additionally, much of the information you suggested for the introduction is already covered in the Discussion section to avoid redundancy.

The Methods section was where the main issues were reported. We acknowledge that our sample size of 13 volleyball players may be relatively small. Before conducting the study, we tried to perform a priori analysis to estimate the necessary sample size. However, as stated in the introduction section, relevant studies to inform this calculation were scarce. Generally, the rule of thumb for this type of study is a sample size of 10-20 individuals per group. To ensure consistency, we tried to reach a sample that not only was homogeneous (sex, age, internal load, external load, etc), but also was routinized on how to perform the exercise, resulting in 13 participants. The other main issue highlighted was the tibia positioning. In this study, the same evaluator manually positioned the leg in three positions (internal, external, neutral). The maximum tibial rotation was determined when no further range of motion could be achieved without compensation. In order to avoid some constraints potentially encountered with this leg stabilization, the athletes performed three correct executions in each position, and mean values were calculated individually. We chose manual positioning to mimic the real-life exercise execution. The Nordic hamstrings exercise usually involves two individuals, where one person performs the exercise by resisting a forward-falling motion from a kneeling position, using their hamstring muscles to maximize loading during the eccentric phase; the second person stabilizes the lower legs/feet with their hands. So, the person who is maintaining the leg might unintentionally rotate for one of the three positions, hypothetically altering the hamstring activation. Our methods reflect this practical variability. Although mechanical positioning could improve reliability, it would not accurately represent real-world conditions. Moreover, some issues were also referred to in the Nordic exercise execution. Regarding those issues, we followed the recommendation of these two studies: Alt, T.; Schmidt, M. The ANHEQ evaluation criteria: introducing reliable rating scales for assessing Nordic hamstring exercise quality. Sports Medicine-Open 2021, 7, 91.; Alt, T.; Severin, J.; Schmidt, M. Quo Vadis Nordic Hamstring Exercise-Related Research?—A Scoping Review Revealing the Need for Improved Methodology and Reporting. International Journal of Environmental Research and Public Health 2022, 19, 11225.

We acknowledge that our study has limitations. Many of these cannot be addressed post hoc. Therefore, we think that many of the issues reported are more suitable in the limitations section (where we have already made additions), rather than making changes in the main text.

We hope this response addresses many of your concerns, and we are open to further constructive feedback.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the opportunity to review this article. I went through this work with pleasure, well developed by the authors, whom I also congratulate. The introduction is correctly made, it conceptually delimits the terms used appropriately. Materials and Methods correctly described, and the results are clearly and objectively presented. The discussions and conclusions are easy to understand, the ideas flow easily, an aspect that complements the accuracy of the presentation. The bibliographic sources are sufficient, most recent and in agreement with the theme. I would not change anything, I would leave the article in its current form.

Author Response

Thank you for your reply. We appreciate the encouragement given in your feedback.

Reviewer 3 Report

Comments and Suggestions for Authors

1.     The keywords must be different from the title.

Introduction

1.     The introduction could benefit from a more detailed explanation of the specific gap this study aims to fill.

2. In the review of existing literature would be beneficial to highlight the novelty of your study more explicitly.

3.     The hypotheses for the study should appear at the end of the introduction.

Methods

1.     The sample is small, which may limit the generalizability of the findings. Consider discussing the implications of this limitation.

2.     The characteristics of the sample, such as age, years of federated practice, body mass and height, should be included in this section.

3.     Porque não fizeram o MVC?

4.     The description of the exercise protocol and EMG procedures could be more detailed. Include diagrams or images of the electrode placement and exercise positions for better understanding.

5.     The statistical methods are appropriate, but the rationale behind the choice of tests should be explained in more detail. Ensure clarity on why specific effect size measures were used.

Results

1.     Clearly differentiate between significant and non-significant findings in the text. Use terms like "statistically significant" to avoid ambiguity.

Discussion

1.     The discussion should explicitly state how these findings contribute to the existing body of knowledge.

2.     The comparison with existing studies could be more extensive.

3.     The limitations section is adequate but could discuss more potential biases and how they were mitigated. For example, discuss the impact of the small sample size and any potential measurement errors in the EMG data.

4. Suggestions for future research are mentioned but could be more specific. Propose concrete future studies that could build on your findings.
5. How can this study help players and coaches?

6.     At the end of the discussion, there should be a list of the hypotheses that should be added at the end of the discussion so that it is possible to conclude whether the study was in line with what was initially hypothesized or not.

Conclusions

 

1. The conclusion summarizes the study well but could be more concise. Highlight the practical implications of the findings for practitioners.

 

 

By addressing these points, the manuscript will be significantly improved in terms of clarity, readability, and scientific rigor.

Comments on the Quality of English Language

• The manuscript is generally well-written but would benefit from a thorough proofread to correct minor grammatical errors and improve flow.

Author Response

Dear reviewer, thank you for your reply. We will respond point-by-point.

Comment 1: The keywords must be different from the title.

Response 1: Thank you for your comment. The keywords were changed.

Comments 2, 3, and 4: The introduction could benefit from a more detailed explanation of the specific gap this study aims to fill; In the review of existing literature would be beneficial to highlight the novelty of your study more explicitly; The hypotheses for the study should appear at the end of the introduction.

Response 2, 3, 4: Thank you for your point this out. Most of this information is provided in the lines 66-75. However, more information was added in the lines 75-81.

Comments 5 and 6: The sample is small, which may limit the generalizability of the findings. Consider discussing the implications of this limitation.; The limitations section is adequate but could discuss more potential biases and how they were mitigated. For example, discuss the impact of the small sample size and any potential measurement errors.

Responses 5 and 6: Thank you for the opportunity to clarify. We agree that the sample size may be small to achieve the relevant statistical analysis. Therefore, as recommended we added a limitation. Nevertheless, as referred to in our introduction, no study performed this analysis on the eccentric strength. Therefore, a previous calculation of the sample size was difficult to make. Therefore, we use the rule of thumb for this analysis, applying the 10-20 individuals per group (in this case, 13 per group)

Comment 7: The characteristics of the sample, such as age, years of federated practice, body mass, and height, should be included in this section.

Response 7: We cordially disagree with your comment. In the methods section we cannot explore these characteristics as, at this stage, we did not apply yet the eligibility criteria. Therefore, we think that is more appropriate for the results section.

Comment 8: Porque não fizeram o MVC?                

Response 8: MVC was not applied because of the fatigue effect and the study design. Our study design was a crossover, where the sample performed three valid repetitions, in three different positions, within the same session. MVC requires maximal effort from the muscles, which can increase the risk of injury, especially in exercises involving intense muscle elongation, like the Nordic hamstring exercise. Performing an MVC can lead to rapid muscle fatigue, which can affect the quality and consistency of subsequent measurements since fatigue can alter form and technique, compromising the validity of the results.

Comment 9: The description of the exercise protocol and EMG procedures could be more detailed. Include diagrams or images of the electrode placement and exercise positions for better understanding.

Response 9: Thank you for your comment. In the manuscript, there is Figure 1 (showing the NHE execution) and Figure 2 (showing the electrode and tibia position).

Comment 10: The statistical methods are appropriate, but the rationale behind the choice of tests should be explained in more detail. Ensure clarity on why specific effect size measures were used.

Response 10: The choice of ANOVA method is appropriate for comparing means across multiple groups, ensuring equal variances and data independence. The selection of effect size measures, such as eta-squared, is based on a clear interpretation of statistical significance and practical relevance of observed differences

Comment 11: Clearly differentiate between significant and non-significant findings in the text. Use terms like "statistically significant" to avoid ambiguity.

Response 11: We are sorry, but we are not understanding where the comment is applicable. The lines 187-188, state that: “Overall, the results indicated no statistically significant differences (p > 0.05) between positions, hamstrings muscles, or sides.” Can you be more specific to know where we need to be clearer?

Comments 12 and 13: The discussion should explicitly state how these findings contribute to the existing body of knowledge.; The comparison with existing studies could be more extensive.

Response 12 and 13: We agree with your comments. We tried our best to do such discussion. However, as stated, the information on the eccentric strength is still scarce. We tried to do so with information from studies that explored other types of strength (namely, concentric and isometric), triangulating with information about the muscle’s behavior under eccentric tension, and the sample's natural lower extremities natural position and demanings of the sport. Nevertheless, if you have specific literature that may refine our study, please let us know.

Comment 14: Suggestions for future research are mentioned but could be more specific. Propose concrete future studies that could build on your findings.

Response 14: Thank you for your comment. Suggestions are provided in the limitations section, namely, other sports, sex, and increased sample. As recommended we added more. Nevertheless, do you have others that may be included? If so, please let us know.

Comments 15, 16, 17: How can this study help players and coaches?; At the end of the discussion, there should be a list of the hypotheses that should be added at the end of the discussion so that it is possible to conclude whether the study was in line with what was initially hypothesized or not. The conclusion summarizes the study well but could be more concise. Highlight the practical implications of the findings for practitioners.

Responses 15, 16, 17: We agree with a change. As recommended in a previous comment, a hypothesis was added, that changed the conclusion.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors, thanks for your revised version and the clarifications.

Sadly even after the clarifications and your edits, I see that you failed to address the serious methodological issues that I raised in terms of design and stats used.

Comments on the Quality of English Language

Minor

Author Response

Comment: 

Dear authors, thanks for your revised version and the clarifications.

Sadly even after the clarifications and your edits, I see that you failed to address the serious methodological issues that I raised in terms of design and stats used.

Response: 

Dear Reviewer,

Thank you once again for taking the time to review our study and provide feedback. We sincerely regret that, despite our efforts to address the issues you raised, there remain concerns.

We understand the importance of rigorous methodology in scientific research and want to reiterate that many of the decisions made in our study were driven by practical considerations related to the nature of the exercise and the conditions under which it is typically performed. While we recognize that some aspects could be refined, we believe these decisions were necessary to maintain ecological validity and to reflect real-world applications of the Nordic Hamstrings Exercise.

Thank you once again for your time and thoughtful review.