Review Reports - Does a Greater Hamstring Muscle Thickness Mean a Greater Aponeurosis Thickness?

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The primary purpose of this study was to investigate whether a significant correlation exists between muscle thickness and the thickness of the superficial and deep layers of the aponeurosis at various points along the hamstrings. Furthermore, it aimed to explore how this relationship might influence the prediction of muscle injuries. While the study is both innovative and interesting, several methodological improvements are necessary to enhance the robustness and relevance of its findings.

One major area for improvement is the diversification of the study population. The study focused exclusively on physically active individuals, excluding other critical groups such as elite athletes, sedentary individuals, and patients with a history of muscle injuries. Including these groups would significantly enhance the generalizability of the findings and their clinical applicability. For example:

Elite athletes: Could provide valuable insights into how intensive training adaptations influence the muscle-aponeurosis relationship.
Patients with prior injuries: Are crucial for understanding how scarring, remodeling, or structural changes affect this correlation.
Sedentary individuals: Could offer a baseline perspective on muscle and aponeurotic structures in the absence of significant mechanical stimuli.

If it is not feasible to include these populations, the study must clearly justify why a specific group was chosen and explain how this decision adds clinical relevance to the research.

Moreover, it is essential to expand the analysis to explore sex-based differences. Evidence suggests that muscle and aponeurotic structures may vary significantly due to hormonal and biomechanical factors. Including a detailed comparison between males and females would enrich the study and broaden its clinical applicability, enabling the identification of sex-specific patterns.

The statistical analysis employed in the study also warrants attention. While the Kolmogorov-Smirnov test was used to assess data normality, this test is not appropriate for sample sizes smaller than 50, as is the case here. Instead, the Shapiro-Wilk test, which is better suited for small sample sizes, should be used to ensure reliable results.

Additionally, incorporating multivariate statistical models is highly recommended to deepen the understanding of the relationships between the studied variables. These models would allow for:

Controlling for confounding variables: Adjusting for factors such as sex, age, body mass, physical activity level, and specific anatomical characteristics of the participants. This would help isolate the direct effects of muscle and aponeurosis thickness.
Evaluating interactions: Exploring the interplay between muscle thickness, superficial aponeurosis thickness, and deep aponeurosis thickness. This approach would provide a clearer understanding of the interrelationships among these dimensions and their functional implications.

These statistical enhancements would not only strengthen the study’s internal validity but also clarify the conclusions, providing a more solid foundation for future research and clinical applications.

This study presents an innovative and clinically relevant approach to a pressing research question. However, to maximize its impact, the study must diversify its population, provide clear justifications for methodological choices, and reinforce its statistical analyses. These improvements would enhance the study’s robustness and ensure that its findings can be applied more broadly and effectively in clinical and athletic contexts.

Author Response

Reviewer 1

Comment: The primary purpose of this study was to investigate whether a significant correlation exists between muscle thickness and the thickness of the superficial and deep layers of the aponeurosis at various points along the hamstrings. Furthermore, it aimed to explore how this relationship might influence the prediction of muscle injuries. While the study is both innovative and interesting, several methodological improvements are necessary to enhance the robustness and relevance of its findings.

Response: Thank you very much for your constructive comments and your positive feedback on our manuscript. Please find below the responses to your comments.

Comment: One major area for improvement is the diversification of the study population. The study focused exclusively on physically active individuals, excluding other critical groups such as elite athletes, sedentary individuals, and patients with a history of muscle injuries. Including these groups would significantly enhance the generalizability of the findings and their clinical applicability. For example:

Elite athletes: Could provide valuable insights into how intensive training adaptations influence the muscle-aponeurosis relationship.
Patients with prior injuries: Are crucial for understanding how scarring, remodeling, or structural changes affect this correlation.
Sedentary individuals: Could offer a baseline perspective on muscle and aponeurotic structures in the absence of significant mechanical stimuli.

If it is not feasible to include these populations, the study must clearly justify why a specific group was chosen and explain how this decision adds clinical relevance to the research.

Response: The decision to include physically active individuals in our study was made to maintain a controlled and homogeneous sample population, which potentially would reduce variability associated with significant differences in physical activity levels, training status, and injury history. This approach was essential for isolating and accurately assessing the relationship between muscle thickness and the thickness of the superficial and deep layers of the aponeurosis providing reference values for the comparisons with other groups. In the revised manuscript, we acknowledge the inclusion of physically healthy individuals as a limitation (Lines 381-382) and have provided a clear justification for selecting this population (Lines 382-386).

Comment: Moreover, it is essential to expand the analysis to explore sex-based differences. Evidence suggests that muscle and aponeurotic structures may vary significantly due to hormonal and biomechanical factors. Including a detailed comparison between males and females would enrich the study and broaden its clinical applicability, enabling the identification of sex-specific patterns.

Response: Please see the comment below. We added in the revised manuscript a multiple regression analysis to adjust for confounding variables such as gender as suggested.

Comment: The statistical analysis employed in the study also warrants attention. While the Kolmogorov-Smirnov test was used to assess data normality, this test is not appropriate for sample sizes smaller than 50, as is the case here. Instead, the Shapiro-Wilk test, which is better suited for small sample sizes, should be used to ensure reliable results.

Response: Following your suggestion, we have reanalyzed the data using the Shapiro-Wilk test, which is more appropriate for small sample sizes. The results confirm that the data's normality remains consistent with the findings obtained using the Kolmogorov-Smirnov test. These changes have been updated in the manuscript accordingly (Line 186).

Comment: Additionally, incorporating multivariate statistical models is highly recommended to deepen the understanding of the relationships between the studied variables. These models would allow for:

Controlling for confounding variables: Adjusting for factors such as sex, age, body mass, physical activity level, and specific anatomical characteristics of the participants. This would help isolate the direct effects of muscle and aponeurosis thickness.
Evaluating interactions: Exploring the interplay between muscle thickness, superficial aponeurosis thickness, and deep aponeurosis thickness. This approach would provide a clearer understanding of the interrelationships among these dimensions and their functional implications.

Response:

Thank you very much for this suggestion, we agree. In response to your comment, we have performed a multivariate regression analysis adjusting for the physical activity, body mass and gender (Lines 177-183). We exclude the age of the participants as a confounding factor due to the homogeneity of the included participants (physically active young individuals). The new statistical analysis did not significantly change the results of the study (Lines 199-201, 223-226, 243-246, 264-266).
To address this, we included interaction terms in our multivariate regression models to assess how these dimensions interrelate and whether their relationship varies based confounding variables like body mass, physical activity, and sex (Lines 177-183).

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The presented work is highly relevant to the fields of rehabilitation therapies, training programs, and injury prevention in high-performance sports. It addresses the analysis of the correlation between the anatomical morphologies of the hamstring muscles and their corresponding aponeuroses. The study was conducted on a sample of 50 physically active individuals. The results are significant, as they reveal limited correlations and substantial variability between these anatomical characteristics.

Based on these findings and the limitations discussed in the study, I have the following question: To what extent can the observed data variability be attributed to the methodology used for the measurements? It is well known that ultrasound techniques may be subject to operator-introduced errors. In this context, would it be possible to estimate the error associated with these measurements from your data? This would allow readers to assess whether the variability observed in the correlated points significantly exceeds the margin of error of the measurements.

Another point of concern relates to the determination of the six ultrasound measurement sites (15%, 30%, … 90%) and the regions used in the analysis: proximal, proximal-middle, middle, distal-middle, and distal. How are these points correlated? Specifically, which measurements taken from the ultrasound images correspond to each of these regions? Clarifying this relationship could enhance the interpretation of the results and their applicability in clinical or sports contexts.

In conclusion, this study provides interesting and valuable data for the areas mentioned at the beginning of this review. Moreover, it opens the door to future research that could address questions such as: What happens with these correlations in elite athletes? or How are these relationships affected by age? These lines of study would serve as a valuable complement to the existing knowledge.

Author Response

Reviewer 2

Comment: The presented work is highly relevant to the fields of rehabilitation therapies, training programs, and injury prevention in high-performance sports. It addresses the analysis of the correlation between the anatomical morphologies of the hamstring muscles and their corresponding aponeuroses. The study was conducted on a sample of 50 physically active individuals. The results are significant, as they reveal limited correlations and substantial variability between these anatomical characteristics.

Response: Thank you very much for the time spending on our manuscript and for your useful suggestions.

Comment: Based on these findings and the limitations discussed in the study, I have the following question: To what extent can the observed data variability be attributed to the methodology used for the measurements? It is well known that ultrasound techniques may be subject to operator-introduced errors. In this context, would it be possible to estimate the error associated with these measurements from your data? This would allow readers to assess whether the variability observed in the correlated points significantly exceeds the margin of error of the measurements.

Response: Reliability analysis of our experimental procedures, including ultrasound measurements and analysis has been performed in our previous study (Sahinis and Kellis 2024). This analysis assessed between-day reliability and demonstrated relatively small measurement errors and high intraclass correlation coefficients, indicating excellent reliability. These findings suggest that operator-introduced variability was minimal and unlikely to significantly contribute to the observed data variability. Additionally, this high variability between individuals has also been observed in previous studies that have examined the proximal muscle tendon unit dimensions of biceps femoris (Evangelidis et al., 2016)

Comment: Another point of concern relates to the determination of the six ultrasound measurement sites (15%, 30%, … 90%) and the regions used in the analysis: proximal, proximal-middle, middle, distal-middle, and distal. How are these points correlated? Specifically, which measurements taken from the ultrasound images correspond to each of these regions? Clarifying this relationship could enhance the interpretation of the results and their applicability in clinical or sports contexts.

Response: Thank you for your comment, to clarify:

The six ultrasound measurement sites along the femur length correspond to equally spaced percentages of the total femur length while the regions represent broader anatomical zones.

These regions corresponding the measurement sites as follows:

- Proximal: 15 and 30%

- Proximal-middle: 30 and 45 %

- Middle: 45 and 60 %

- Distal-middle: 60 and 75%

- Distal: 75% and 90%

After obtaining the ultrasound images at the six measurement sites, each site provided 60 datapoints, resulting in a total of 360 datapoints per participant. For analysis, each measurement site was subdivided into 72 evenly spaced datapoints along the width of the muscle
Each region's data integrates the respective measurement sites' results. For instance, the "proximal" region uses the values from the 15 and 30% measurement site, while the "middle" region aggregates data from the 30 and 45% site.

This information was now included in the revised manuscript (Lines 158-161).

Comment: In conclusion, this study provides interesting and valuable data for the areas mentioned at the beginning of this review. Moreover, it opens the door to future research that could address questions such as: What happens with these correlations in elite athletes? or How are these relationships affected by age? These lines of study would serve as a valuable complement to the existing knowledge.

Response: We agree that the inclusion of diverse population could significantly improve the applicability of the present findings. However, the decision to include only physically active individuals was made to maintain a controlled and homogeneous sample population, which potentially would reduce variability associated with significant differences in physical activity levels, age, training status, and injury history. This approach was essential for isolating and accurately assessing the relationship between muscle thickness and the thickness of the superficial and deep layers of the aponeurosis providing reference values for the comparisons with other groups. In the revised manuscript, we acknowledge the inclusion of physically healthy individuals as a limitation (Lines 381-382) and have provided a clear justification for selecting this population (Lines 382-386).

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Your paper covered an interesting and cleared up some issues.

The only change I would recommend is on the second line of the abstract.

In this sentence you indicate you have 50 subjects, but the numbers you give only add up to 49. However, in the methods you indicate you have 28 males and 22 females. Which of these numbers are correct?

Author Response

Reviewer 3

Comment: Your paper covered an interesting and cleared up some issues. The only change I would recommend is on the second line of the abstract. In this sentence you indicate you have 50 subjects, but the numbers you give only add up to 49. However, in the methods you indicate you have 28 males and 22 females. Which of these numbers are correct?

Response: Thank you for your positive feedback on our manuscript. We included 50 participants (28 males and 22 females), this section of the abstract is now updated.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept in present form

Author Response

Thank you for your helpful comments provided for our manuscript

Reviewer 2 Report

Comments and Suggestions for Authors

After reviewing the responses provided by the authors, I find no objections to supporting the publication of their results. As a final recommendation, I suggest conducting a thorough review of the manuscript to ensure it is free from typographical or grammatical errors that could affect its presentation.

Author Response

Comment: After reviewing the responses provided by the authors, I find no objections to supporting the publication of their results. As a final recommendation, I suggest conducting a thorough review of the manuscript to ensure it is free from typographical or grammatical errors that could affect its presentation.

Response: Thank you very much for your constructive comments. We have read again the manuscript as suggested