Comparison of Strength Adaptation Responses Among Individuals with Different Muscle Fiber Type Profiles

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

please see attached

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 1,

We sincerely appreciate the time and effort you have devoted to reviewing our manuscript. We fully understand how valuable your time is and we are truly grateful for your careful reading, insightful observations, and constructive comments.

Please find attached our detailed response document, in which we have addressed each comment point by point.

We believe that your suggestions have significantly helped us improve the quality and clarity of the manuscript.

Thank you again for your valuable contribution.

Sincerely,
Corresponding Author

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addresses a relevant topic in resistance training and muscle physiology; however, the current version presents substantial methodological, conceptual, and interpretative weaknesses that considerably limit the scientific validity of the findings. The major concern is the indirect and insufficiently validated classification of muscle fiber types, combined with the absence of direct hypertrophy measurements, lack of a control group, and limited statistical robustness. Several conclusions are overstated relative to the design and available data.

Specific commentaries:

Line 24-29: The manuscript repeatedly refers to “muscle hypertrophy,” yet no direct hypertrophy measurements (e.g., muscle thickness, CSA, ultrasound, DXA, MRI) were collected; the terminology should be revised to “strength adaptations” throughout the manuscript.

Line 27-29: The study objective is ambiguously formulated because it claims to examine “strength development” while the title focuses on “muscle hypertrophy responses”; the objective and title should be aligned.

Line 31-39: The quasi-experimental design without a control group substantially weakens causal inference; the authors should justify this design more rigorously or temper all causal interpretations.

Line 34-36: The classification of muscle fiber type using repetitions at 80% 1RM is highly indirect and insufficiently validated to support categorical assignment into Type I, Type II, and Mixed groups.

Line 35-36: The manuscript should provide reliability and validity evidence for the repetition-based muscle fiber classification method in trained bodybuilding populations.

Line 41-43: The authors report percentage improvements but do not provide confidence intervals or variability estimates for these changes; inferential statistics for change scores should be expanded.

Line 45-47: The conclusion overstates the practical implications considering the indirect estimation of muscle fiber composition and lack of mechanistic measurements.

Line 63-67: The statement that 30–80% of hypertrophy potential is genetically determined is overly broad and should be contextualized with more recent evidence.

Line 82-87: The authors present indirect testing methods as widely accepted alternatives, yet the limitations and controversies surrounding these methods are insufficiently discussed.

Line 89-95: The literature gap is not convincingly established; the introduction requires a clearer synthesis of previous studies specifically comparing resistance training adaptations across muscle fiber typologies.

Line 96-100: The rationale should explain why only bench press performance was selected to represent generalized training adaptation across multiple muscle groups.

Line 101-113: The justification for the chosen design is weak because the absence of randomization and control conditions introduces multiple confounding variables that are not controlled statistically.

Line 114-116: The hypothesis includes “hypertrophy development,” but hypertrophy was never directly assessed; this represents a major conceptual inconsistency.

Line 120-127: The study design section lacks sufficient detail regarding allocation procedures and whether baseline equivalence between groups was tested.

Line 130-140: No sample size calculation or a priori power analysis is presented; a post hoc power analysis alone is insufficient to justify adequacy of the sample.

Line 136-137: Dietary intake was not monitored or standardized, despite nutrition being a major determinant of hypertrophy and strength adaptation.

Line 137-138: The instruction to “refrain from participating in activities involving physical activity” is unrealistic and insufficiently operationalized for trained athletes.

Line 160-184: The exclusion criteria mention anabolic agents and supplements, but no verification procedure (questionnaire, screening, biochemical verification) is described.

Line 186-196: The manuscript lacks information regarding test-retest reliability and standardization procedures for 1RM assessment.

Line 193-196: Loads for non-bench press exercises were determined “through observational assessments,” which introduces substantial measurement bias and poor reproducibility.

Line 197-203: The rationale linking bench press performance to generalized skeletal muscle fiber distribution is scientifically weak because muscle fiber composition varies considerably between muscle groups.

Line 205-212: The 1RM testing protocol lacks information regarding rest intervals between attempts and whether standardized spotting procedures were used.

Line 215-221: The cut-off values used for muscle fiber classification appear arbitrary and should be supported with stronger validation evidence.

Line 224-230: The acknowledgment that the classification is only a “phenotypic proxy” substantially undermines the strength of the main conclusions and should be emphasized more clearly in the discussion and conclusion.

Line 231-236: The absence of progressive overload during the 6-week intervention is a major methodological limitation because progressive loading is a fundamental principle of resistance training adaptation.

Line 233-235: Training at fixed 80% 1RM for six weeks without load adjustment likely altered relative intensity over time and may have affected group comparisons.

Line 237-242: The rationale for maintaining constant loads contradicts established resistance training principles and may have limited ecological validity.

Line 243-258: The statistical analysis section does not report whether baseline group differences were assessed prior to comparing change scores.

Line 248-251: Multiple pairwise comparisons were conducted without any adjustment for type I error (e.g., Bonferroni correction), increasing the risk of false-positive findings.

Line 257-258: The post hoc power analysis is insufficiently described; the effect size assumptions and software parameters should be reported.

Line 271-273: Non-normality was assessed only for pooled data; normality and homogeneity should also be examined separately for each group.

Line 274-283: The manuscript reports a very large effect size for the intervention, yet without a control group it is impossible to determine whether improvements exceed expected training effects or measurement variability.

Line 278-286: Reporting both mean ± SD and median (Q1–Q3) without clear justification creates inconsistency in data presentation.

Line 292-295: Table 8 is unclear because it does not explicitly state whether analyses were performed on raw post-test values or delta changes.

Line 296-303: The intergroup analysis lacks effect sizes and confidence intervals, limiting interpretation of the practical significance of the findings.

Line 305-308: Figure 2 presents percentage changes without error bars or variability measures, reducing interpretability and statistical transparency.

Line 312-321: The discussion repeatedly attributes findings to muscle fiber composition despite the absence of direct physiological assessment.

Line 323-324: Neural adaptations are mentioned but not measured; therefore, mechanistic explanations should be presented more cautiously.

Line 333-343: The discussion relies heavily on indirect repetition-based assumptions while overlooking the large interindividual variability in repetition capacity unrelated to fiber type.

Line 350-358: The manuscript acknowledges that repetition performance is multifactorial, yet the conclusions still strongly emphasize muscle fiber typology.

Line 364-365: The explanation involving “greater recruitment of high-threshold motor units” is speculative because no EMG or neuromuscular assessment was conducted.

Line 367-373: The manuscript correctly recognizes neural adaptations as contributors to strength gains; however, this further weakens the central claim regarding hypertrophy and fiber-type-specific adaptation.

Line 375-378: The practical recommendations for individualized training programs are premature given the methodological limitations and indirect classification approach.

Line 380-399: The conclusion section is excessively descriptive and repeats methodological details instead of emphasizing scientifically supported interpretations.

Line 390-399: The authors should avoid implying causal relationships between muscle fiber type and adaptation magnitude because the study design cannot establish causality.

Line 401-428: The limitations section is appropriate but indirectly confirms that the central variable of the study (muscle fiber type) was not accurately measured; this issue substantially compromises the validity of the conclusions.

Line 410-414: The explanation regarding pectoral muscles and type II growth is speculative and unsupported by data collected in the study.

Line 415-423: The manuscript itself acknowledges the weak scientific validation of the indirect performance tests used; therefore, stronger caution is required in the interpretation of results.

Line 454-553: Several references are outdated or not directly related to the specific research question; the literature review should incorporate more recent high-quality evidence on resistance training adaptations and muscle fiber typology.

Author Response

Dear Reviewer 2,

We sincerely appreciate the time and effort you have devoted to reviewing our manuscript. We fully understand how valuable your time is and we are truly grateful for your careful reading, insightful observations, and constructive comments.

Please find attached our detailed response document, in which we have addressed each comment point by point.

We believe that your suggestions have significantly helped us improve the quality and clarity of the manuscript.

Thank you again for your valuable contribution.

Sincerely,
Corresponding Author

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

The study addresses an interesting and practically relevant question: whether individuals classified according to different functional muscle fiber-type profiles show different adaptations to the same resistance training protocol. The topic has clear relevance for individualized resistance training prescription.

The main concern is that the manuscript repeatedly frames the study as being about muscle hypertrophy, while the measured outcome appears to be maximal strength performance, specifically 1RM in the bench press. No direct measure of hypertrophy, such as muscle thickness, cross-sectional area, ultrasound, DXA, circumference, or other morphological assessment, is reported. For this reason, the title, abstract, aim, discussion, and conclusion should be revised to focus on strength development or 1RM performance rather than hypertrophy.

The classification of participants into Type I, Type II, and Mixed groups is based on the number of repetitions completed at 80% of 1RM. This should be described consistently as an indirect, performance-based, functional estimate of fiber-type typology, not as direct determination of muscle fiber composition. The wording throughout the manuscript should be made more cautious to avoid implying that the actual histological fiber composition was measured.

There is a potential circularity in the methodology. Participants were classified using performance at 80% of 1RM, and then trained using a protocol also based on 80% of 1RM and 8-12 repetitions. This may partly predetermine group differences in response. The authors should explicitly discuss this issue and clarify how participants classified as Type II, who, by definition, performed fewer repetitions at 80% of 1RM, were able to complete training sets in the prescribed 8-12 repetition range without adjusting the load.

The lack of a control group and randomization limits the causal interpretation of the findings. Improvements in 1RM may reflect the training intervention, as well as familiarization with testing, technical learning, motivation, recovery, or other uncontrolled factors. The conclusions should therefore be softened and presented as associations rather than definitive causal effects.

The intervention requires further clarification. The authors state that loads were kept constant throughout the six-week period. If participants improved over time, the initial 80% 1RM load would progressively represent a lower relative intensity. This has implications for interpreting the training stimulus. Please clarify whether loads were adjusted, whether proximity to failure was monitored, whether session adherence was recorded, and whether tempo, range of motion, rest intervals, and technical execution were standardized.

The statistical analysis should be strengthened. The manuscript should report pre-test and post-test values separately for each group, not only global values. Baseline comparability between groups should be shown. Between-group comparisons of change should include effect sizes and confidence intervals. Post-hoc comparisons should include correction for multiple testing. The analysis would also be improved by using an approach that adjusts for baseline values, such as ANCOVA, a mixed model, or an appropriate non-parametric alternative.

The post hoc power analysis adds limited value in its current form. A clearer justification of sample size, or greater emphasis on confidence intervals and precision of estimates, would be more informative.

The discussion appropriately acknowledges some limitations, particularly the indirect assessment of fiber typology and the possible role of neural adaptations. However, these points should be integrated more strongly into the interpretation of the results. Since the intervention lasted only six weeks, neural adaptations may explain a substantial part of the observed 1RM improvement, which limits conclusions about morphological adaptation.

The generalizability of the findings should be stated more clearly. The sample included only young male fitness and bodybuilding athletes with prior training experience. The results should not be generalized to women, older adults, untrained individuals, clinical populations, elite athletes, or other muscle groups without caution.

The manuscript would benefit from substantial language editing. There are several typographical and grammatical issues, such as spelling errors and inconsistent capitalization of group names. The tables also require formatting and clarification, particularly the statistical tables and the training protocol table.

In Table 9, values reported as “.000” should be clarified. If these refer to p-values, they should be reported as “p < .001” rather than “p = .000”. The table should also clearly distinguish U values, Z values, and p-values.

Overall, the manuscript has potential, but it requires major revision. The strongest route to improvement would be to reframe the article as an exploratory study of maximal strength changes according to an indirect repetition-based typology, moderate the conclusions, strengthen the statistical reporting, and remove or substantially qualify claims related to hypertrophy and directly measured muscle fiber composition.

Kind regards,

Comments on the Quality of English Language

The reference base could be improved by adding more directly relevant studies on indirect fiber-type estimation, validity of repetition-based tests, and strength versus hypertrophy outcomes. The main issue is not the absence of references, but the mismatch between claims about hypertrophy and the actual 1RM-based outcome measured in the study.

Author Response

Dear Reviewer 3,

We sincerely appreciate the time and effort you have devoted to reviewing our manuscript. We fully understand how valuable your time is and we are truly grateful for your careful reading, insightful observations, and constructive comments.

Please find attached our detailed response document, in which we have addressed each comment point by point.

We believe that your suggestions have significantly helped us improve the quality and clarity of the manuscript.

Thank you again for your valuable contribution.

Sincerely,
Corresponding Author

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I am happy with the revised version and have no further recommendations. 

Author Response

Dear Reviewer,

I sincerely thank you for the time, attention, and effort you have given to evaluating my manuscript. I greatly appreciate your observations and suggestions, which have significantly contributed to the improvement of the work.

I am glad that the changes made meet expectations and I am grateful for the constructive feedback provided during the review process.

With respect,
Dan Iulian Alexe

Reviewer 2 Report

Comments and Suggestions for Authors

No more commentaries.

Author Response

Dear Reviewer 2,

I sincerely thank you for the time, attention, and effort you have given to evaluating my manuscript. I greatly appreciate your observations and suggestions, which have significantly contributed to the improvement of the work.

I am glad that the changes made meet expectations and I am grateful for the constructive feedback provided during the review process.

With respect,
Dan Iulian Alexe

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

The revised manuscript has improved compared with the previous version. The change in title toward "Strength Adaptation Responses" is appropriate and better aligned with the actual outcome assessed, namely 1RM performance rather than direct muscle hypertrophy. The authors also responded constructively to the main concern that muscle fiber type was estimated indirectly and should not be interpreted as a direct histological measurement. The revised manuscript now states that the 80% 1RM repetition-based test is a functional, performance-oriented proxy rather than a direct physiological measurement, which strengthens the interpretative caution of the study.

The authors´ response letter adequately acknowledges several previous concerns, including the overemphasis on hypertrophy, the indirect classification of muscle fiber typology, the absence of a control group, the lack of randomization, the possible role of neural adaptations, and the need to frame the study as exploratory.

Despite these improvements, important scientific and methodological limitations remain. The study is still based on a quasi-experimental single-group pre-test/post-test design without a control group or randomization. This limits causal inference, and the findings should continue to be presented primarily as exploratory associations rather than evidence that fiber type determines training adaptation. The manuscript acknowledges this limitation, but some statements still remain more definitive than the design allows.

The main methodological concern remains the potential circularity between the classification procedure and the intervention. Participants were classified according to repetitions performed at 80% 1RM, and the training intervention was also prescribed at 80% 1RM with an 8-12 repetition range. This should be discussed more explicitly as a central limitation, not only as a minor methodological issue. It remains possible that the grouping procedure partly shaped the observed between-group differences.

The intervention description has improved, but relevant training-control details remain insufficient for a robust interpretation. The authors state that training loads were intentionally kept constant for six weeks, but this means that the relative intensity likely decreased as participants adapted. This is important because the intervention is interpreted as a standardized strength stimulus. The absence of progressive load adjustment, direct monitoring of proximity to failure, and detailed control of volume load or effort should be more clearly integrated into the interpretation of the findings.

The statistical reporting has improved, but the analysis remains limited. The manuscript reports non-parametric testing and comparisons of pre-post differences between groups, but it would still benefit from clearer baseline comparability between groups, group-specific pre-test and post-test descriptive values, effect sizes for between-group comparisons, confidence intervals, and correction for multiple comparisons. The decision not to apply ANCOVA or mixed models is acknowledged in the response letter, but this still limits the strength of the conclusions.

The conclusions are more cautious than in the previous version and now acknowledge that the absence of a control group and indirect fiber-type estimation prevent definitive generalization. This is an important improvement. However, the conclusions should be further refined to avoid implying that true muscle fiber composition was measured or that training response can be attributed primarily to fiber typology. The findings are better described as differences in 1RM adaptation associated with a repetition-based functional typology in young trained men.

Overall, the revised manuscript is scientifically clearer and more appropriately framed than the previous submission. However, the central limitations of design, indirect classification, possible circularity, and limited statistical adjustment remain. The article may be considered further if presented explicitly as an exploratory study with cautious interpretation, avoiding any strong causal claims about muscle fiber composition or hypertrophy.

Kind regards,

Author Response

Dear Reviewer,

I sincerely thank you for the time, attention and effort you have given to evaluating my manuscript. I greatly appreciate your observations and suggestions, which have significantly contributed to the improvement of the work.

I am glad that the changes made meet expectations and I am grateful for the constructive feedback provided during the review process.

Please review our responses in the attachment.

With consideration,
Dan Iulian Alexe

Author Response File: Author Response.pdf