EXcellence and PERformance in Track and Field (EXPERT)—A Mixed-Longitudinal Study on Growth, Biological Maturation, Performance, and Health in Young Athletes: Baseline Results (Part 2)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Introduction

The introduction is clearly written and establishes a coherent theoretical framework linking physical, psychological, and environmental determinants of youth athletic development. The cited literature is relevant and appropriately supports the key constructs addressed, including biological maturation, motivation, and perseverance. However, part of the discussion on psychological traits—particularly grit—draws on evidence from other sports (e.g., swimming and diving). While this contributes to a broader understanding, incorporating references or arguments more specific to athletics could strengthen the internal consistency of the rationale.

Furthermore, the stated aim of the study is primarily descriptive, focusing on the characterization of growth, maturation, and motivation in young athletes. Although this aligns with the study’s cross-sectional nature, adding a more analytical or interpretive dimension could enhance the scientific depth and alignment with the experimental orientation commonly valued by JFMK.

Materials and Methods

The methodological section is generally clear and detailed, particularly regarding the description of measurement protocols in the individual domain, which are consistent with international kinanthropometric standards. However, some methodological aspects would benefit from clarification or further justification.

First, the study refers to a mixed-longitudinal design, but the current manuscript presents only baseline data without specifying the intended follow-up duration, competitive seasons, or measurement intervals. Clarifying these elements would help contextualize the longitudinal scope and strengthen the coherence between design and objectives.

Second, while the inclusion of effect size estimation (ω²) is noted, it remains unclear whether effect sizes were systematically interpreted to assess the practical significance of the findings. Given the large sample and the number of comparisons, a clear explanation of how effect sizes were handled and interpreted would enhance methodological transparency.

Third, in the motor performance domain, strength-related variables are comprehensively addressed through multiple tests, but endurance is represented solely by a 1000 m run without a specific bibliographic reference or validation source. Similarly, the single-arm throwing test lacks details regarding the type and mass of the implement used, as well as references supporting its application to youth track and field populations. Providing such information or referencing prior validation studies would ensure reproducibility and scientific robustness.

Fourth, the club domain questionnaire provides relevant contextual information, yet it appears to be a study-specific instrument without reported psychometric validation. Although exploratory tools can be justified in field-based studies, a brief discussion of its development process or reliability assessment would be valuable.

Finally, the use of ANOVA and ANCOVA is appropriate for analyzing sex and age differences in cross-sectional data. However, if the broader project aims to generate longitudinal evidence, it would be important to indicate whether mixed-model approaches or repeated-measures analyses are planned for subsequent phases, ensuring alignment between the analytical strategy and the study design.

Results Section
General comment
The Results section is well organized into four coherent subsections (anthropometry and body composition; motivation and perseverance; motor performance; and club characteristics). The structure follows the three analytical domains defined in the EXPERT study and provides a detailed presentation of findings supported by tables and supplementary figures. Nevertheless, several aspects could be improved to enhance statistical transparency, visual clarity, and interpretive balance.
 Anthropometry and body composition
The description of anthropometric and body composition data is complete and methodologically consistent with the applied two-way ANOVA (sex × age). The inclusion of F-values, p-values, and effect sizes (ω²) adds analytical value. However, the text tends to reproduce numerical results without sufficient synthesis or emphasis on developmental patterns. A more integrative approach highlighting key transitions—such as the reversal of height and strength advantages between 12 and 13 years or the influence of maturity offset on sex divergence—would improve readability and interpretation.
Stylistically, the subsection meets scientific standards, though the notation of interactions should be standardized (“age × sex” instead of “edad×sexo”). Finally, the maturity-offset results are reported accurately, but their functional or athletic relevance remains unaddressed, weakening the connection to the subsequent discussion.
 Motivation and perseverance
The use of ANCOVA is appropriate because psychological variables are sensitive to chronological age. However, two methodological and one formal issue deserve attention:
 Sample reduction: The decrease from 425 to 128 athletes is not discussed. This substantial loss (> 70 %) limits representativeness and should be explicitly acknowledged, clarifying that questionnaires were administered only to athletes aged ≥ 12 years.
Effect-size interpretation: Although ω² values are reported, their magnitude (small, moderate, or large) is never interpreted, which limits the practical understanding of the results.
Formatting issue in Table 2: The table appears visually misaligned—shifted to the right, with line numbers or markers remaining on the left margin—making it difficult to read across rows. This layout problem should be corrected prior to publication, as it directly affects readability and comprehension.
Overall, the results confirm the expected trends (higher intrinsic motivation and enjoyment among girls), but the section would benefit from clearer comments on the proportion of variance explained by the covariate and a concise interpretation of the observed effects.

Motor performance
This is among the technically strongest parts of the manuscript. The two-way ANOVA is well justified, and the findings are appropriately supported by Supplementary Figures 2 (Figs. 7–22). The age- and sex-related trends are coherent with existing evidence, and the breadth of physical tests is commendable.
However:
The subsection is overloaded with raw F- and p-values, which hinders interpretive clarity. Summarizing results by type of ability (strength, speed, jump, endurance) would provide a clearer synthesis.
Effect sizes are provided but not interpreted; including a short explanation of their magnitude thresholds would enhance the analytical rigor.
•Some performance tests (e.g., 1000 m run, single-arm throw) lack bibliographic validation references; this omission, already noted in the Methods section, should be briefly reiterated here to reinforce transparency.
The supplementary figures correctly reflect age × sex interactions, but figure captions are too generic (p ≤ 0.05 without specifying comparisons) and do not indicate whether bars represent SD or SE; this should be clarified.
 Club characteristics
Table 4 adequately fulfills its descriptive purpose but must be interpreted cautiously since the club questionnaire lacks psychometric validation. The authors handle the data descriptively (frequencies and percentages), which is appropriate, yet they should clearly state that the instrument is exploratory and cannot infer quality, efficiency, or causal relations with athlete development.
The subsection is clearly written but would benefit from:
•    indicating the number of clubs surveyed at the beginning;
•    explaining how missing data were handled;
•    revising table alignment and typography for consistency; and
•    adding a short integrative comment linking infrastructural limitations to potential developmental implications, thus improving the transition to the Discussion.

Discussion

The Discussion section follows an appropriate structural logic, but its development is unbalanced. Some subsections are overly descriptive, while others lack analytical depth or coherence with the study’s stated aims. The interpretation does not always align with the introductory framework, and certain arguments remain conceptually fragmented. The following detailed comments address each subsection.

Anthropometry, Body Composition, and Biological Maturation

This subsection is excessively long and descriptive, with numerous cross-study comparisons that obscure the main developmental tendencies. The authors list age- and sex-related differences but fail to synthesize them into a clear developmental trend. The discussion should be condensed to emphasize the general trajectory—linear increase in stature and lean mass, reversal of female advantage around ages 13–14, and widening sex differences in fat and fat-free mass—rather than restating numerical contrasts. A more conceptual synthesis would enhance interpretive clarity and better connect to the practical implications of growth and maturation in young athletes.

Motivation and Perseverance

The discussion focuses almost exclusively on sex differences, with no examination of age-related evolution or the developmental progression of motivation and perseverance across the 10–14 age range. This omission limits interpretive value, as this period is critical for shaping intrinsic motivation and self-efficacy in youth sport. The absence of any temporal analysis or reflection on potential motivational change weakens the subsection’s depth.
Moreover, the treatment of grit remains confined to sex comparisons, without exploring contextual or maturational dimensions. It would strengthen the discussion to acknowledge explicitly the absence of age-related variation as a meaningful result in itself, interpreting motivational stability across early adolescence as an important developmental feature rather than a limitation.

Performance

The discussion of aerobic endurance lacks internal coherence. Although the study used a 1000 m running test, the authors compare their results to studies employing shuttle-run or other distances (800–1500 m) without clarifying the methodological differences. This leads to inconsistent reasoning, as the physiological demands and performance determinants differ substantially across protocols. In addition, the endurance test was not theoretically introduced or justified in the Introduction, leaving this discussion disconnected from the original framework. It should be reformulated to delineate the specific relevance of the 1000 m test in athletics and to avoid extrapolations between non-equivalent assessments.
Beyond this issue, the remainder of the performance discussion is coherent and technically sound, though it would benefit from a clearer identification of which motor capacities are most sensitive to growth (e.g., explosive strength and sprint speed) and which remain relatively stable (e.g., agility).

Clubs

This subsection is the least convincing in interpretive terms. The comparison between multi-sport and single-sport clubs is not analytically relevant in the context of this study, as it does not relate to athlete performance or development variables. Furthermore, the contrasts with data from other sports (football, basketball) or other countries may provide contextual reference but are not generalizable to the Portuguese case due to structural and economic disparities.
The text would benefit from a concise, synthetic paragraph summarizing general findings: small club size, limited multidisciplinary teams, lack of specialized staff, and infrastructure constraints. Such a synthesis would yield more generalizable insights and avoid unnecessary cross-sport comparisons. Additionally, the discussion omits a minimal methodological description of the club questionnaire, which hinders the evaluation of data reliability.

The limitations are well presented and appropriately balanced. The authors clearly acknowledge the restricted age range, the cross-sectional nature of the baseline data, and the limited regional representativeness. These statements are pertinent and proportionate to the study’s scope. One additional limitation should be noted: the absence of psychometric validation for the club questionnaire, which further constrains generalization and comparability.

Conclusions

The Conclusions are clear, well structured, and effectively summarize the main findings of the study, offering a comprehensive overview of the anthropometric, motivational, and performance-related development of young track and field athletes in major Portuguese cities. The section maintains internal coherence and accurately reflects the results discussed throughout the paper.
However, from a methodological standpoint, several of the broader statements—particularly those concerning  club context—would benefit from stronger methodological support. The validity of these conclusions depends largely on the robustness of the instruments employed, some of which (notably the club questionnaire) were exploratory and lacked psychometric validation.
The conclusions appropriately position the study within the framework of the ongoing longitudinal EXPERT project, presenting a valuable snapshot of youth athletics development in Portugal. Nevertheless, the interpretive claims about the interaction of biological, psychological, and contextual factors should be presented with caution until longitudinal data are available. Likewise, remarks concerning club organization and resources should explicitly acknowledge the methodological constraints of the survey.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article aims to: This study aims to design and validate a community-based nursing strategy for the prescription of physical activity in vulnerable populations, integrating key social determinants of health to analyse their influence on accessibility, adherence, and the overall effectiveness of the intervention.

The authors are requested to address the following points:

• Body fat percentage and fat mass were measured using a Tanita BC-553 device; however, the manuscript does not report the hydration control protocol, the time elapsed since the last meal, clothing/shoe considerations, or the specific equation applied for paediatric populations.
• There is no evidence of a sample size calculation, statistical power estimation, or criteria for representativeness. The manuscript does not clarify whether the sample of 425 participants is sufficient for the numerous tests and comparisons performed.
• A large number of statistical tests are presented (multiple variables and interactions), yet no corrections for multiple comparisons (e.g., Bonferroni, FDR) are described. Multiple p-values and ω² statistics are reported without adjustment.
• The analysis does not control for several relevant confounding variables (training hours, sport specialisation, training age, socioeconomic status).
• Although the manuscript mentions data cleaning and outlier detection, it does not specify the criteria used or the number of cases excluded for each variable.
• ω² effect sizes are reported for main effects and interactions, but without confidence intervals or a clear interpretation of their magnitude (small/medium/large).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear authors,

please refer to the attached review

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revised version of the manuscript shows a clear improvement compared with the previous submission. The authors have adequately addressed the main points raised during the review process, particularly with regard to the coherence of the introduction, the alignment between objectives, methods, and results, and the overall balance of the discussion.
The methodological approach is appropriate and clearly described. The statistical analyses are correctly applied, and the psychological instruments used are validated and suitably integrated into the study design. The Results section is consistent with the Methods, and the Discussion provides a reasonable and cautious interpretation of the findings within a developmental framework.
Only minor revisions are recommended at this stage, mainly related to improving clarity and synthesis in some parts of the text. These adjustments are editorial in nature and do not affect the scientific quality or validity of the study.

Author Response

We would like to thank the reviewer for the positive and constructive feedback on the revised version of our manuscript. In response to this last comment, we have carefully revised the entire document to further improve clarity and conciseness, as suggested. In addition, all tables and figures were thoroughly reviewed and refined to enhance their quality and readability.

Thank you again for your valuable comments, which have helped improve the final version of our work.