Review Reports - The Latent Dimensionality of Physical and Technical Performance Across Three Youth Soccer Tiers

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

I greatly appreciate the effort you have made in addressing my comments. I believe that the quality of the manuscript and the impact of the results have improved following the revision process.

I would still suggest that you include descriptive statistics, possibly as supplementary material to the manuscript.

Author Response

Dear Reviewer,

We would like to thank you for contributing to the substantial improvement of our

manuscript.

Please find the detailed responses below and the corresponding revisions/corrections highlighted in the re-submitted file.

Kind regards,

The authors

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

Dear authors,
Thank you for your responses to the first review; I appreciate the effort you have made to improve your manuscript, particularly in relation to methodological aspects that influence the study’s discussion and conclusions.
I have set out below the points that should be revised to strengthen the analytical and interpretative rigour of the study, particularly the report on the factor analysis, which is still incomplete (lack of KMO, Bartlett’s test results, and communalities), and the justification for the use of PCA and Varimax rotation, which requires greater conceptual clarity. Furthermore, I note a discrepancy between the results and the conclusions that need to be clarified before publication. Finally, the stated limitation regarding the absence of indicators of biological maturity needs to be addressed in greater depth in the discussion.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

We would like to thank you for contributing to the substantial improvement of our

manuscript.

Please find the detailed responses and the corresponding revisions/corrections

highlighted in the re-submitted file.

Kind regards,

The authors

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

Dear Authors,
I confirm that you have addressed the suggestions from the second review. Therefore, I consider the manuscript approved for publication.
Excellent work.
Sincerely

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

Thank you for the opportunity to review your manuscript. The study addresses a relevant topic by analyzing latent dimensions of anthropometric, physical, and technical variables in young footballers.

In general terms, the manuscript has an adequate structure; however, I believe that some improvements are needed to strengthen its conceptual and methodological rigour. I suggest reinforcing the state of the art and the justification for the study, improving the clarity of the methodology section, and expanding the factorial analysis report by incorporating statistical information that allows for a more accurate evaluation of the quality of the model.

Likewise, the discussion could benefit from greater integration with the existing literature and a more cautious interpretation of some results.

Below, I present specific comments organised by section of the manuscript.

Kind regards.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for your interest in our paper and for your useful advices.

A point-by-point response to your comments are listed in the box below and revised version of the manuscript is uploaded as a Word file (please see the attachment):

Introduction

In general, it is suggested that the conceptual framework and state of the art be organised considering anthropometric, physical and technical domains, and that recent studies identifying latent factors in youth football be continued.

Point 1: Lines 50-54: Citations are missing.

Response: Authors have added missing reference.

Point 2: Line 55: Review the conceptual basis of explosive strength and power as a motor skill.

Response: As suggested, the sentence has been revised.

Point 3: Rows 57-58: A transition is needed in the state of the art of anthropometric variables and physical abilities to understand the idea outlined.

Response: A transition sentence has been added between Lines 57 and 58. This clarifies the relationship between anthropometry and physical abilities.

Point 4: Row 61: More biomechanical justification or solid empirical evidence is required regarding the association between upper limb muscle strength and lower limb power.

Response: Thank you for pointing this out. We have expanded Line 61 to include a biomechanical justification.

Point 5: Rows 75 to 87: I suggest reviewing these studies to account for the current state of the art on the point they raise or rethinking the argument that justifies conducting their study.

https://doi.org/10.3390/app14177569

https://doi.org/10.3390/jfmk10010040

https://doi.org/10.47197/retos.v61.110400

Response: We agree that the study rationale should focus on the conceptual necessity of the research. We have revised the introduction to acknowledge the current state.

Point 6: At the end of the section, it is suggested that the justification for the study be strengthened, emphasizing why it is important to analyze latent dimensions beyond mentioning development by age and why factor analysis adds value to the study.

Response: We agree that the methodological rationale needed more depth. We have added a concluding paragraph to the Introduction explaining that latent dimension analysis is essential for identifying the primary constructs of performance

Materials and methods

Point 7: Line 94: There is a need to justify why a cross-sectional design is appropriate for inferring the latent structure of anthropometric variables of physical capacities and motor skills specific to football.

Response: We have addressed this by adding a justification at the end of the Introduction. We clarify that the cross-sectional design was selected to identify stable latent structures at specific developmental milestones while minimizing the confounding effects of individual longitudinal training variability.

Point 8: Line 107: Indicate the type of sampling.

Response: The manuscript has been revised (Line 107) to specify the sampling method. A cluster sampling approach was employed.

Point 9: Justify why biological maturation was not considered as a potential factor.

Response: We acknowledge that biological maturation is a significant factor in youth performance. However, this study focused on the latent structural organization of performance traits within established competitive age categories (chronological age), rather than individual development. To mitigate the influence of maturation variance, we employed a large sample size (N=427) and strictly adhered to the competitive tiers defined by the national football association. While the lack of maturation data is a limitation, which we have explicitly addressed in the Limitations section.

Point 10: Line 110: Greater methodological clarity is required. The grouping indicated generates an overlap between ages (11-13, 13-15, 15-17). For example, 13 and 15-year-olds appear in two categories. It would be advisable to explicitly explain the competitive categories used (U13, U15, U17) and the corresponding years of birth: U13 (11-12 years); U15 (13-14 years); U17 (15-16 years).

Response: We appreciate the reviewer's concern regarding the age overlap. To clarify, the groups were formed based on birth years in accordance with the Serbian Football Association's competitive regulations. We have revised the text (Line 111) to explicitly state that the categories are mutually exclusive and have updated the nomenclature to U13, U15, and U17 to avoid further ambiguity.

Point 11: Line 123: It is suggested to justify why these specific tests would be appropriate for declaring latent dimensions in young football players.

Response: These variables have been shown in previous studies to representatively assess each of the segments covered in this research

Point 12: Line 124: Cite studies that support the variables considered in the study.

Response: Cited.

Point 13: Line 127: Justify and specify the procedures of the tests applied.

Response: We have expand the Procedure section.

Point 14: Line 128: It is necessary to specify the assessment criteria according to ISAK and the expertise of the assessors, according to ISAK criteria (level 3).

Response: We have specify this more detailed in the Procedure section.

Point 15: Lines 129 to 125: The joint inclusion of these anthropometric measurements in the factor analysis needs to be justified.

Response: We appreciate the reviewer's technical observation. The decision to include a diverse set of anthropometric variables in a single factor analysis is based on the multi-dimensional model of morphological space. Following the reviewer's suggestion, we have added a brief methodological justification in the textto clarify the rationale for the inclusion of these specific variables.

Point 16: Line 136: The validity of the motor skills tests selected for the population of young footballers (the citation refers to the EUROFIT test) has not been indicated. It is suggested that the selection of these tests as part of the physical abilities dimension be justified.

Response: We have added a methodological justification to the manuscript clarifying that basic motor tests were included to define the foundational physical substrate necessary for youth soccer players.

Point 17: Line 145: It is suggested that the validity and current relevance of the selected battery be justified.

Response: We agree with the reviewer’s suggestion. The manuscript has been updated to include a methodological justification for the specific motor skill battery. Authors have added a reference in the 2.2 Sample of Procedures section.

Point 18: Line 215: It is necessary to specify whether there was a standardized warm-up before the application of the tests, or to specify what it consisted of.

Response: Thank you for the comment. Authors have added a warm up description in the Procedure section.

Point 19: It is suggested that you indicate whether pilot tests were carried out.

Response: Although a formal pilot study was not conducted, a comprehensive familiarization session and preliminary protocol testing were carried out with the participants. This ensured that the players were fully acquainted with the technical demands of each test and that all equipment was accurately calibrated before the formal data collection began. We have added this clarification to Section 2.3.

Point 20: It is necessary to indicate how fatigue was controlled, specifying rest times between tests and whether there was a random order to avoid bias.

Response: We agree that fatigue control is essential for the validity of motor and technical assessments. The protocol included standardized recovery intervals: 1 minute between consecutive attempts and 5 to 10 minutes between different tests. The manuscript has been updated in Section 2.3 to specify these intervals.

Point 21: It is important to clarify the decision to take the tests on the same day rather than over two days to avoid fatigue.

Response: We appreciate the opportunity to clarify this logistical decision. All measurements were conducted on the same day to ensure identical climatic and environmental conditions for all participants, as well as to maintain consistent levels of motivation. To prevent any impact of fatigue on the results, we implemented a rigorous recovery protocol (1-minute rest between trials and 5–10 minutes between tests). The manuscript has been updated in Section 2.3 to reflect this justification.

Point 22: Line 284. It is suggested to justify the factorial method, specifying whether it is principal component analysis or factor analysis (common factor analysis).

Response: We confirm that Principal Component Analysis (PCA) was employed as the factorial method and it was modified in the Statistical analysis section.

Point 23: It is suggested that the KMO (Kaiser-Meyer-Olkin) be indicated to assess the suitability of the sample for factor analysis.

Response: The suitability of the data for factor analysis is clearly demonstrated by the robust and stable factor structure obtained across all age groups. High factor loadings (many exceeding 0.70 and 0.80) and the logical clustering of variables provide empirical evidence of high sampling adequacy.

Point 24: It is suggested that Bartlett's sphericity test be included to assess whether the correlation matrix is different from an identity matrix.

Response: We agree with the reviewer’s suggestion. The Bartlett's test of sphericity was employed to verify that the correlation matrix significantly differed from an identity matrix.

Point 25: The threshold for factor loadings has not been indicated. What was the cut-off for considering loadings significant? (>0.40 or >0.50)

Response: We appreciate the reviewer’s request for clarification. The threshold for considering factor loadings as significant was set at >0.40 in the Statistical section.

Point 26: Indicate whether you evaluated communalities or variables with low saturation.

Response: We evaluated both the communalities and variables with low factor saturation. All variables were found to have acceptable communalities, indicating that they contributed meaningfully to the overall variance. While some variables exhibited lower saturation (loadings < 0.40) on certain factors, they were retained in the final model to maintain a comprehensive representation of the athletes' morphological and motor profiles.

Point 27: The description of the factorial procedure could benefit from greater methodological detail, as key elements for evaluating the suitability of the method are missing

Response: We agree that a more detailed description of the factor analysis procedure enhances the methodological transparency of the study. Accordingly, we have expanded Section Statistical Analysis

Results

Point 28: 1. The presentation structure is clear. Results are reported by age group and variable type, and the figures complement the textual explanation well.

Response: We sincerely thank the reviewer for this positive feedback regarding the clarity of our results presentation and the quality of the figures.

Point 29: 2. It is suggested that the general patterns be summarized, considering that the presentation is excessively narrative and offers an extensive description of each factor.

Response: We appreciate this constructive suggestion. We agree that the extensive description of each factor could be simplified to highlight broader trends. In the revised manuscript, we have condensed the individual factor descriptions and added a summary paragraph at the end of the Results section.

Point 30: 3. It is suggested that a complete table with factor loadings, including communalities and the variance explained by each factor, be presented in a standard format. This would facilitate the evaluation of the quality of the model and the interpretation of the factorial structure.

Point 31: 4. We suggest improving the quality of the factor analysis report by explicitly explaining the eigenvalues of each factor, the cumulative variance explained, and the factor loadings that support the interpretation and naming of the factors.

Point 32: 5. It is also recommended to indicate the criteria used to interpret the factor loadings (e.g., the minimum threshold considered significant).

Response: We have added in the Statistical analysis section.

Point 33: 6. It is suggested that the description of the factors be summarized. Instead of listing all the loadings, it could be noted, for example: Factor 1 grouped variables related to speed with and without the ball, with loadings between 0.59 and 0.73. This could improve the flow without losing content.

Response: We have followed the reviewer’s suggestion and significantly condensed the description of the factors. Instead of listing every individual loading, we now present the interpreted factors by highlighting the functional groups of variables and their loading ranges. This has improved the clarity and flow of the Results section while retaining all essential statistical information.

Point 34: 6. The interpretation of the factors could be presented more concisely, avoiding repetition in the wording and directly describing the dimension represented by each factor. The results should be 100% descriptive, without speculation: Line 455: Example: "Based on this, we can define it as a factor of segmental speed of the lower extremities with and without the ball." Therefore, it is suggested to reduce the discussion within the results.

Response: We removed all interpretive phrases (e.g., 'Based on this...') to ensure the section remains descriptive.

Discussion

Point 35: 1. The discussion tends to repeat the description of the factorial results rather than delvingb into their biomechanical or functional significance.

Response: We have shifted the focus from a repetitive description of the factor analysis results to a more meaningful interpretation of their functional and biomechanical significance

Point 36: 2. Further research is needed into the practical and theoretical implications of the emergence of three, four, or two factors in each age group, particularly in relation to performance in youth football.

Response: We agree with the reviewer’s suggestion. We have expanded the discussion on the practical and theoretical implications of our findings.

Point 37: 3. The discussion could be strengthened by a more systematic dialogue with previous studies that have analyzed anthropometric profiles or latent performance structures in young footballers.

We suggest reviewing:

https://doi.org/10.3390/su13147713

https://doi.org/10.1519/JSC.0000000000003416

Response: We agree with the reviewer that a more systematic comparison with existing literature enhances the depth of our discussion. Accordingly, we have expanded the Discussion section to include a direct dialogue with recent studies.

Point 38: 4. Line 501: The interpretation of factor 1 as a general motor performance factor could be nuanced, as factor analysis identifies patterns of covariation between variables but does not necessarily imply the existence of an underlying causal construct.

Response: We acknowledge that factor analysis identifies patterns of covariation and does not inherently prove a causal construct. In response, we have revised the text (Line 501) to offer a more nuanced interpretation.

Point 39: 5. The interpretation of the shift from a general performance factor in early ages to greater specialization in later ages could benefit from greater bibliographic support in the literature on motor development in young football talents.

Response: We agree that the interpretation of the shift from general to specialized motor structures is a crucial finding. In the revised manuscript, we have integrated references to classic models of motor development.

Point 40: 6. It is suggested that the concepts used (e.g., 'motor performance', 'general physical performance', and 'motor ability') be clarified, as they appear to be used interchangeably throughout the text.

Response: We removed general phyisical perfrormance in text.

Point 41: 7. Line 518: It is suggested that more references be included in some statements (e.g., Elzen) to strengthen theoretical support for these interpretations.

Response: More references were added in the Discussion section.

Point 42: 8. Line 523: The differences observed between age groups are attributed to neuromuscular maturation processes. However, given that the study does not include direct indicators of biological maturation, this interpretation could be qualified or supported with further evidence from the literature.

Response: The interpretation is now supported with further evidence from literature.

Point 43: 9. Lines 528-536: Revise statements about predominant types of training at different stages of development that appear speculative, considering that the study does not evaluate specific training programs. It may be necessary to delve deeper into the current evidence on types of training that intersect with their results from specific studies.

https://doi.org/10.3389/fphys.2024.1502694

https://pmc.ncbi.nlm.nih.gov/articles/PMC8669935/

Response: Thank you for the comment. We have revised this part in the Discussion.

Point 44: 10. Line 531: Studies supporting this statement (studies on speed and power with age) are not cited.

https://doi.org/10.3389/fphys.2024.1502694

https://doi.org/10.1007/s11332-025-01352-7

Response: We have citet studies you suggested.

Point 45: 10. Line 547: While it is correctly recognized that factor analysis can simplify complex biological processes, this reflection could be expanded to consider additional factors that influence the development of young footballers, such as biological maturation, training experience, or the effect of relative age.

Response: Thank you for the comment. Authors have expaned this part.

Point 46: Conclusion

The conclusion indicates that two latent dimensions consisting of anthropometric variables

were identified; however, multiple factors were reported in the results for some age groups.

It is suggested that this synthesis be clarified to ensure consistency with the results

presented.

Response: We have revised the Conclusion to ensure consistency with the Results section.

Kind regards,

The authors

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addresses a potentially relevant topic; however, it is affected by major methodological shortcomings that significantly weaken the validity of the findings.

First, the authors fail to provide any information regarding who administered the tests and their level of training or expertise. Moreover, no reliability data are reported, which raises serious concerns about the consistency and reproducibility of the measurements.

The so-called sport-specific tests are neither validated nor supported by any evidence justifying their selection. In addition, their procedures and rationale are only superficially described, limiting the reader’s ability to understand and replicate the methodology.

Several tests appear to lack ecological validity in relation to the actual demands and dynamics of soccer performance. Furthermore, some tests labeled as “soccer-specific” do not meet this criterion and would be more appropriately classified as general motor skills assessments.

The manuscript also lacks essential descriptive statistics for the outcomes across the three groups in the individual tests, which prevents a clear understanding of the data.

The presentation and interpretation of the factor analysis are insufficiently detailed, making it difficult to evaluate the robustness and meaning of the results.

Finally, the authors do not consider positional differences (i.e., roles), which represent a critical contextual variable—particularly in the pioneer and cadet categories—and may substantially influence the development of specific skills.

Overall, these issues substantially limit the scientific rigor and interpretability of the study.

Author Response

Dear Reviewer,

Thank you very much for your interest in our paper and for your useful advices.

A point-by-point response to your comments are listed in the box below and revised version of the manuscript is uploaded as a Word file (please see the attachment):

Point 1: The manuscript addresses a potentially relevant topic; however, it is affected by major methodological shortcomings that significantly weaken the validity of the findings.

Response: Thank you for the comment. We have updated method section and clarified who administered the tests.

Point 2: The so-called sport-specific tests are neither validated nor supported by any evidence justifying their selection. In addition, their procedures and rationale are only superficially described, limiting the reader’s ability to understand and replicate the methodology.

Response: We have updated the manuscript with supporting references regarding our tests and variables.

Point 3: Several tests appear to lack ecological validity in relation to the actual demands and dynamics of soccer performance. Furthermore, some tests labeled as “soccer-specific” do not meet this criterion and would be more appropriately classified as general motor skills assessments.

Response: We appreciate this insightful observation. While these tests evaluate fundamental movement patterns, we categorized them as 'specific' because the inclusion of the ball-handling component significantly alters the coordination dynamics and attentional demands compared to general motor tasks.

Point 4: The manuscript also lacks essential descriptive statistics for the outcomes across the three groups in the individual tests, which prevents a clear understanding of the data.

Response: The authors acknowledge the reviewer’s suggestion to include descriptive statistics for each individual test. However, given that this study analyzes a large battery of 23 specific motor tests and 13 anthropometric variables across three distinct age groups, including full descriptive tables for every individual outcome would result in an excessive amount of data.

Point 5: The presentation and interpretation of the factor analysis are insufficiently detailed, making it difficult to evaluate the robustness and meaning of the results.

Response: As suggested by the reviewer, the factor analysis report has been enhanced. We have now explicitly included eigenvalues for each factor, the total cumulative variance, and specific factor loadings to provide a more robust statistical interpretation and justify the naming of the identified motor dimensions.

Point 6: Finally, the authors do not consider positional differences (i.e., roles), which represent a critical contextual variable—particularly in the pioneer and cadet categories—and may substantially influence the development of specific skills. Overall, these issues substantially limit the scientific rigor and interpretability of the study.

Response: We agree with the reviewer that playing positions are a crucial contextual variable that significantly influences the development of specific motor and technical skills, especially in older cohorts. However, the primary aim of this study was to establish a general developmental framework for the latent structure of abilities across different age categories. However, we have now addressed this point in the 'Limitations' section of the Discussion, suggesting that future research should incorporate positional roles to further refine the specialized profiles of young soccer players.

Author Response File: Author Response.docx