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Thank you for diligently addressing the reviewer feedback. Your manuscript is now suitable for acceptance and publication.
[# PeerJ Staff Note - this decision was reviewed and approved by Mike Climstein, a PeerJ Section Editor covering this Section #]
The reviewers have identified areas for strengthening the manuscript. Largely, these relate to reducing the strength of language in the conclusions and discussion. Please respond to the the reviewer feedback and provide evidence of modification or rebuttal in your resubmission.
The manuscript is generally well written in clear and professional English. The revisions made since the prior round have improved clarity, particularly in the Abstract (sample size, surgery types) and Introduction (added statistics and prior findings). Figures and tables are appropriately labeled, and raw data and code have been provided.
Remaining areas for improvement:
Some sentences in the Introduction remain lengthy and could be streamlined further to sharpen the rationale and knowledge gap.
While Table 1 now presents effect sizes, Figure 1 still functions more as a procedural illustration than a data figure. Consider clarifying its caption to highlight why the setup is relevant to interpretation.
Minor typographical inconsistencies remain (e.g., spacing around “p≤0.05” or subscripts like “N∙cm-2”), which should be corrected in final proofing.
The research question is well defined and relevant, and the authors have appropriately clarified ethical approval, inclusion/exclusion criteria, and recruitment procedures. These revisions strengthen methodological transparency.
Remaining concerns:
The reliance on convenience sampling and inclusion of only athletes “cleared” for return to sport likely introduces selection bias. This limitation should be acknowledged more explicitly in the Methods as well as the Discussion.
The use of handheld dynamometry is pragmatic, but its limitations compared to isokinetic testing should be emphasized in the Methods. The Discussion now notes discrepancies with prior studies, but the methodological constraints should be flagged earlier.
The training history of the healthy control group (SAM) was not collected, which limits the interpretation of group differences. While this is mentioned in the Discussion, it should also be acknowledged upfront as a design limitation.
The statistical analyses are appropriate and well reported with p-values and effect sizes. The conclusions are mostly consistent with the data, and the authors now emphasize sample size and power limitations.
Remaining issues:
The Discussion sometimes attributes observed differences (e.g., greater hamstrings strength in POST) to rehabilitation program effectiveness. Given the study’s design and small sample size, these claims should be softened to avoid causal inference. It would be more accurate to state that the findings are consistent with effective rehabilitation but cannot confirm causality.
The sample size (n=18) remains underpowered to detect subtle effects. The risk of Type II error is acknowledged, but should be more strongly emphasized as limiting the generalizability of the results.
Functional outcomes (e.g., rate of force development, balance, jump testing) were not included. This restricts the applicability of the findings, and the need for multimodal assessment should be reinforced in the Conclusions.
The study addresses an important question in sports rehabilitation and demonstrates the feasibility of combining ultrasound imaging and strength testing in return-to-sport evaluations.
The addition of effect sizes and clearer reporting of group sizes strengthens the paper.
I encourage the authors to further temper causal language in the Abstract and Conclusions to reflect the exploratory, pilot-scale nature of the study.
With these adjustments, the manuscript could make a useful contribution as preliminary evidence that warrants replication in larger, more diverse cohorts.
The article is interesting and provides a strong addition to the benefits of sports.
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**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.
Quadriceps and hamstrings muscle size and strength comparison between post-operative and healthy individuals
Title
It could be improved by adding the clarification "after knee surgery" to reduce ambiguity.
Note:
The title is publishable in this format, but it would be more powerful if it read: Comparison of quadriceps and hamstrings muscle size and strength between young athletes post-knee surgery and healthy controls.
Abstract:
- The sample size is missing in the abstract.
- It is preferable to clarify the type of surgery (ACL? meniscus?) as it may affect interpretation.
I suggest rephrasing the conclusion in the abstract to be more specific:
These results suggest that the rehabilitation program was effective in restoring quadriceps function and enhancing hamstring strength in young athletes following knee surgery.
Introduction:
- Lacks a comprehensive list of the magnitude of the problem in numbers or global statistics (e.g., the percentage of athletes undergoing knee surgery).
- No specific reference to the types of injuries/surgeries included (ACL? Meniscal? Multiple?).
- It would have been better to include similar studies and their results briefly to clarify where this study differs or agrees.
- Add a short paragraph presenting the magnitude of the problem in numbers (e.g., An estimated X% of young athletes experience knee injuries requiring surgery annually).
- Include examples of previous study results, especially those that found weakness in the quadriceps muscle or improvement in the hamstring muscle.
- Clarify the type of surgery (if applicable) or state that it is multiple.
Method
- The number of participants is not clearly stated in the Participants section (it would be better to state the number of each group here).
- There is no mention of the body that granted ethical approval (IRB approval), which is very important.
- The post-surgery period (how many months after surgery) is not mentioned, a crucial piece of information that affects interpretation.
- There is no clear description of the sample selection method (was it random? Purposive sampling?)
- Add the number of participants for each group within the Participants section.
- Include text about the ethics committee approval and state the approval number.
- Specify the time period after surgery.
- Clarify the method of participant selection.
Result
- There are no accompanying tables or graphs in this text. Their presence is very important to clarify the results.
- The effect size is not mentioned, although the p-value alone is not sufficient for scientific judgment.
- Some results (e.g., "no significant interaction") could be presented in summary tables instead of lengthy text.
- The total sample size is not stated in the results presentation (although the numbers are mentioned later in the results).
- Add a table summarizing all ANOVA results with p-values and effect sizes.
- Provide a graph (bar graph or scatter plot) showing the difference in MVIC_ABS and MVIC_REL between the two groups.
- Clearly state the sample size (n) for each variable.
- State the effect size (Cohen's d or η²), especially for significant results.
Discussion
- The explanation for the superiority of hamstrings in the POST group was not sufficiently expanded.
- There are no clear suggestions for future studies.
- A clearer clinical implication of the outcome would have been preferable.
- Some non-significant variables were not commented on (why were there no differences in the quadriceps?)
- Broaden the discussion by providing deeper physiological explanations for the superior hamstring strength.
- Recommend future studies with larger sample sizes and longer follow-up periods.
- Highlight the clinical implications of these results for designing athlete rehabilitation programs.
Conclusion
- Consider summarizing the study's limitations briefly in the conclusion for greater objectivity.
- Conclude with a direct call for future research involving different surgical types and larger sample sizes.
Best Regards
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**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.
The manuscript is generally well-written in clear and professional English. The authors employ appropriate terminology throughout, making the content accessible to an academic and clinical audience. That said, minor grammatical inconsistencies—such as occasional awkward punctuation and inconsistent use of hyphenated terms like "cross-sectional area"—should be addressed to enhance readability and flow.
The introduction effectively contextualizes the study, referencing a range of relevant and up-to-date sources that underscore the importance of post-operative rehabilitation in sports medicine. Key literature concerning ACL reconstruction, limb asymmetry, and strength recovery is cited. However, the manuscript would benefit from more clearly defining its specific contribution to the existing literature. While the authors reference prior research, they should better articulate what makes their study unique—for instance, simultaneous assessment of muscle size and relative strength using panoramic ultrasound and dynamometry in athletes at the point of return to sport.
Figure 1 supports the methodology by illustrating the dynamometry setup and is appropriately placed and labeled, though it would benefit from higher resolution for better visual clarity. Table 1 is detailed and neatly presents the main outcomes across groups and limbs. Including effect sizes (e.g., Cohen’s d) in the table itself would add interpretive value for readers.
The raw data and supplemental materials are appropriately referenced and appear to be provided in accordance with journal policy. This transparency supports the reproducibility of the research and meets PeerJ’s data sharing standards.
The research question is well-defined and highly relevant to both clinical rehabilitation and return-to-sport decision-making. The study aims to compare quadriceps and hamstring muscle characteristics between post-operative individuals and healthy, matched controls, which is a meaningful contribution to sports medicine and physiotherapy practice.
The use of a case-control design is appropriate for addressing the research question. Participant inclusion and exclusion criteria are clearly outlined, and the methodological steps are adequately detailed. However, the small sample size (n=9 per group) significantly limits the study’s statistical power and generalizability. Although the authors acknowledge this, they should further discuss how this limitation affects the risk of Type II error and the interpretability of their findings.
The authors report proper ethical clearance and informed consent procedures, adhering to the standards for research involving human participants. This reinforces the ethical validity of the study.
Methodological details—particularly regarding ultrasound imaging, strength testing, and statistical analysis—are sufficient to support replication. The authors provide detailed information on equipment, protocols, and measurement sites. Still, while intra-rater reliability is reported and impressive, the manuscript should at least comment on inter-rater reliability to recognize potential variability in image analysis, even if it was not assessed.
The statistical approach—primarily 2x2 mixed factorial ANOVAs and effect size measures—is appropriate for the study design. The authors also provide interpretations using both partial eta squared and Cohen’s d, which strengthens the robustness of their analysis. However, due to the small sample size, the manuscript should emphasize the risk of underpowered analyses and avoid interpreting non-significant findings as evidence of equivalence.
The findings suggest that quadriceps size and strength were similar between the post-operative and control groups, while hamstrings strength was significantly greater in the post-operative group. These results are presented clearly and align with the reported statistical values. The conclusion that rehabilitation protocols may have successfully restored or even enhanced muscle function in the post-operative group is plausible. However, the authors should also address potential selection bias—such as whether more motivated or higher-performing athletes were more likely to be cleared for return to sport and included in the study.
The discussion thoughtfully compares findings to prior literature and considers possible reasons for differences in results, including variations in measurement techniques and rehabilitation focus. This comparative analysis adds depth to the interpretation and shows critical engagement with the field.
The manuscript addresses a clinically meaningful and relatively underexplored area: muscle recovery status in athletes following orthopedic knee surgery. The study's use of advanced imaging (panoramic ultrasound) and accessible clinical tools (handheld dynamometry) enhances its relevance for both research and applied settings. Its structure—from introduction to discussion—is logically organized, and the argument is easy to follow.
There are several areas where the manuscript can be strengthened. First, the small sample size should be more prominently discussed, including potential implications on the strength of conclusions and interpretation of non-significant results. Second, future work should include broader functional measures, such as balance, agility, or jump performance, to create a more complete assessment of post-operative recovery. Third, collecting data on participants’ training history or rehabilitation protocols would enhance understanding of group differences—especially given the unexpected finding of superior hamstrings strength in the post-operative group. Lastly, attention to consistency in abbreviation use and terminology would improve clarity.
Title
It could be improved by adding the clarification "after knee surgery" to reduce ambiguity.
Note:
The title is publishable in this format, but it would be more powerful if it read: Comparison of Quadriceps and Hamstrings Muscle Size and Strength between Young Athletes Post-Knee Surgery and Healthy Controls
Abstract:
- The sample size is missing in the abstract.
- It is preferable to clarify the type of surgery (ACL? meniscus?) as it may affect interpretation.
Recommendation:
I suggest rephrasing the conclusion in the abstract to be more specific:
These results suggest that the rehabilitation program was effective in restoring quadriceps function and enhancing hamstring strength in young athletes following knee surgery.
Introduction:
Points for improvement:
- Lacks a comprehensive list of the magnitude of the problem in numbers or global statistics (e.g., the percentage of athletes undergoing knee surgery).
- No specific reference to the types of injuries/surgeries included (ACL? Meniscal? Multiple?).
- It would have been better to include similar studies and their results briefly to clarify where this study differs or agrees.
Improvement recommendations:
- Add a short paragraph presenting the magnitude of the problem in numbers (e.g., An estimated X% of young athletes experience knee injuries requiring surgery annually).
- Include examples of previous study results, especially those that found weakness in the quadriceps muscle or improvement in the hamstring muscle.
- Clarify the type of surgery (if applicable) or state that it is multiple.
Method
Points for improvement:
- The number of participants is not clearly stated in the Participants section (it would be better to state the number of each group here).
- There is no mention of the body that granted ethical approval (IRB approval), which is very important.
- The post-surgery period (how many months after surgery) is not mentioned, a crucial piece of information that affects interpretation.
- There is no clear description of the sample selection method (was it random? Purposive sampling?)
Improvement recommendations:
- Add the number of participants for each group within the Participants section.
- Include text about the ethics committee approval and state the approval number.
- Specify the time period after surgery.
- Clarify the method of participant selection.
Result
Points for Improvement:
- There are no accompanying tables or graphs in this text. Their presence is very important to clarify the results.
- The effect size is not mentioned, although the p-value alone is not sufficient for scientific judgment.
- Some results (e.g., "no significant interaction") could be presented in summary tables instead of lengthy text.
- The total sample size is not stated in the results presentation (although the numbers are mentioned later in the results).
Improvement Recommendations:
- Add a table summarizing all ANOVA results with p-values and effect sizes.
- Provide a graph (bar graph or scatter plot) showing the difference in MVIC_ABS and MVIC_REL between the two groups.
- Clearly state the sample size (n) for each variable.
- State the effect size (Cohen's d or η²), especially for significant results.
Discussion
Points for Improvement:
- The explanation for the superiority of hamstrings in the POST group was not sufficiently expanded.
- There are no clear suggestions for future studies.
- A more clear clinical implication of the outcome would have been preferable.
- Some non-significant variables were not commented on (why were there no differences in the quadriceps?)
Recommendations for Improvement:
- Broaden the discussion by providing deeper physiological explanations for the superior hamstrings strength.
- Recommend future studies with larger sample sizes and longer follow-up periods.
- Highlight the clinical implications of these results for designing athlete rehabilitation programs.
Conclusion
Recommendations for Improvement:
- Consider summarizing the study's limitations briefly in the conclusion for greater objectivity.
- Conclude with a direct call for future research involving different surgical types and larger sample sizes.
Best Regards
no coment
no coment
no coment
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