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I am happy with the revision made by the authors, and the manuscript is ready for publication.
[# PeerJ Staff Note - this decision was reviewed and approved by Mike Climstein, a PeerJ Section Editor covering this Section #]
Please address the comments from Reviewer 3
1. The manuscript is written in clear, precise, and professional English, with improved flow and logical structuring of sections, making it easy to follow for both researchers and practitioners.
2. The background and literature review provide a comprehensive and up-to-date overview, integrating recent high-quality studies and situating the work well within the broader field of sports science.
1. The comprehensive multi-database search strategy, combined with manual reference list screening, reflects a thorough and systematic approach to study identification.
2. The data extraction, risk of bias assessment, and statistical methods (including sensitivity analyses) are described in detail for replication.
1. The conclusions are consistent with the results, remain within the scope of the data, and provide practical recommendations for athletes and coaches.
1. The discussion section is well-balanced, integrating theoretical mechanisms, practical implications, and relevant literature to contextualize the results.
2. The manuscript makes a valuable contribution to applied sports science by providing evidence-based insights for optimizing core training programs.
Specific Comments
Methods
The manuscript states the literature search covered studies published "up to December 2024". This is a typographical error and should be corrected to December 2023 or the actual end date of the search.
There is a direct contradiction in the description of the statistical analysis. Lines 435-440 state that subgroup analyses and meta-regression were not performed due to the limited number of studies. However, lines 441-449 state that meta-regression was conducted to explore sources of heterogeneity. Please reconcile this and provide a single, consistent account of the analyses that were performed.
Results
In the meta-analysis for sprint performance (Figure 4), the study by Wang (2024) is a significant outlier with a very large effect size and a small weight (0.8%). While the general sensitivity analysis is mentioned, it would greatly enhance transparency and robustness to explicitly state the pooled effect size for sprint performance when the Wang (2024) study is removed in the "leave-one-out" analysis. This would show the reader how much that single study influences the overall result.
In the forest plot figures (Figures 2, 3, and 4), the results column is labeled "IV, Fixed, 95% CI". Given that a random-effects model was correctly used for pooling due to high heterogeneity, this label could be confusing. Please add a note to each figure caption clarifying that the overall diamond represents a pooled estimate from a random-effects model.
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1. The manuscript is written in generally clear and professional English, though minor grammatical refinements are suggested throughout (e.g., line 45–46: “has been as the capacity…” should read “has been defined as the capacity…”).
2. The introduction provides a well-contextualized background and clearly outlines the rationale behind the study.
3. The literature is current and well-cited, with appropriate references supporting all major points.
4. The abstract succinctly summarizes objectives, methodology, key findings, and conclusions.
5. Figures and tables are relevant, well-labelled, and support the narrative.
6. Data availability and registration (INPLASY2023100048) are appropriately declared.
1. The research question is well-defined and addresses a clear knowledge gap in the comparative effectiveness of ICT vs TCT on trunk strength and sprint performance.
2. The use of PRISMA guidelines and the PICOS framework enhances the transparency and reproducibility of the systematic review and meta-analysis.
3. Search strategy across six databases is comprehensive, and inclusion/exclusion criteria are detailed and justified.
4. Use of the PEDro scale for risk of bias assessment is appropriate.
5. Data extraction and synthesis methods are described with clarity.
1. The findings are statistically sound with appropriate meta-analytic methods and effect size interpretation.
2. Results are robust across multiple athletic populations and training contexts.
3. Sensitivity and Egger’s tests are used to assess publication bias—commendable.
1. Strong theoretical justification for the advantage of ICT over TCT.
2. Thorough classification and breakdown of trunk strength components and sprint metrics.
3. The discussion thoughtfully integrates findings with prior research.
4. Limitations are appropriately acknowledged.
Introduction
Several ideas regarding stabilization functions are repeated throughout the introduction. I recommend condensing this section to avoid redundancy and improve flow.
The introduction lacks a dedicated paragraph that clearly outlines specific gaps in the literature beyond the general statement of “a lack of systematic reviews.” It would be valuable to quantify how many comparative studies currently exist and specify which populations are underrepresented.
Methods
Registration and Protocol
Please provide the active hyperlink to the INPLASY registration (INPLASY2023100048) and confirm that the registration date preceded the initiation of the database searches. This would enhance transparency and methodological rigor.
Search Strategy
For clarity, specify the language filters applied (e.g., English only?) and describe how grey literature and manual reference screening were handled. Including an appendix with the full search strings for each database would substantially strengthen replicability.
Eligibility Criteria (PICOS)
Clarify the definition of “healthy athletes” (e.g., are individuals with minor injuries excluded?). Additionally, elaborate on the inclusion of non-randomized trials and clearly state the exact inclusion and exclusion criteria to minimize ambiguity.
Study Selection
Indicate how many reviewers screened the studies at each phase and report the inter-rater agreement using Cohen’s κ coefficient. Also, describe how discrepancies were resolved (e.g., through discussion, third-party adjudication) to reinforce the robustness of the selection process.
Risk of Bias Assessment
Instead of reporting only the total PEDro scores, I recommend presenting a detailed item-by-item risk of bias table for each study. Also, describe how disagreements in scoring were addressed to ensure transparency.
Quantitative Synthesis
It is essential to specify and justify the statistical model used (fixed-effect vs. random-effects). Given that heterogeneity (I²) exceeded 75% in several analyses, sensitivity analyses or meta-regressions are strongly recommended to explore potential sources of heterogeneity.
Results
High Heterogeneity
With I² values ranging from 79% to 91% in stabilization strength and above 90% in dynamic strength, subgroup analyses are urgently needed (e.g., protocol duration, type of sport, unstable surface). Additionally, report the exact p-values from the Q-test to contextualize the observed variability.
Effect Estimates
Please complement the reported effect sizes and 95% confidence intervals with precise p-values. Where applicable, consider applying corrections for multiple comparisons. Furthermore, disaggregate sprint-related outcomes by athletic level or sport modality to provide more actionable insights for practice.
Publication Bias
Include full funnel plots and report the quantitative results from Egger’s test. This will allow readers to better assess the robustness and potential bias in the results.
Graphical Presentation
Enhance the resolution and clarity of the forest plots by using descriptive titles, clearly labeled axes, and more detailed legends. In high-impact journals, such improvements substantially increase the interpretability of findings.
Discussion
The discussion appears overly favorable toward ICT and would benefit from a more balanced tone. Please give greater attention to studies reporting non-significant findings and offer specific hypotheses to explain these inconsistencies.
Consider expanding on clinical implications: based on the findings, which 6–12 week protocols would be most appropriate, depending on the sport or athletic population?
Conclusion
While the conclusions are aligned with the results and study objectives, they reiterate previously reported findings at length. I suggest condensing this section into 3–4 key takeaway sentences and proposing concrete directions for future research (e.g., combined ICT + TCT interventions).
General Comments
This systematic review and meta-analysis explores the impact of instability core training versus traditional core training on trunk strength and sprint performance in athletes. While the research question is certainly pertinent to sports science, the study, in its current form, presents several significant methodological and analytical issues. These concerns, unfortunately, substantially limit the validity and, more importantly, the generalizability of its findings.
Major Weaknesses
Perhaps the most critical limitation stems from the exceptionally high statistical heterogeneity observed across all meta-analyses (I² = 84-95%). This level of heterogeneity fundamentally undermines the suitability of statistically pooling these studies. Such pronounced heterogeneity strongly suggests that the included studies might be measuring different constructs or involve distinct populations, rendering their statistical combination inappropriate. Although the authors acknowledge this considerable heterogeneity, they unfortunately fall short in adequately addressing its implications or thoroughly exploring its sources through appropriate subgroup analyses.
Furthermore, the modest number of included studies (n=12) and the relatively small total participant count (664 individuals) severely restrict the generalizability of any conclusions drawn. It's also worth noting that several studies incorporated into the meta-analysis utilized varying outcome measures, training protocols, and even different athlete populations. This variability raises legitimate questions about the clinical meaningfulness of the reported pooled effect sizes. The intervention protocols themselves exhibited substantial differences in equipment types, training durations (ranging from 6 to 12 weeks), frequencies (2-3 sessions per week), and intensities. This makes it highly questionable whether these disparate interventions genuinely represent a consistent "intervention construct", and it very likely contributes to the high statistical heterogeneity observed.
Minor Weaknesses
On a slightly less critical note, the manuscript contains some formatting errors and inconsistencies, which do detract from its overall professional presentation. Additionally, there appear to be inconsistencies in the search strategy timeline, and certain methodological details could benefit from greater specificity. Finally, the discussion section tends to overstate the strength of the conclusions, particularly when considering the significant limitations identified throughout the study.
Specific Comments
Title and Abstract
Page 1, Line 45: There's a formatting error with "&J&"; it should correctly read "defined".
Page 1, Lines 28-29: For improved clarity, the PEDro score range should specify the total possible score (e.g., "5-7 out of 10 points").
Page 1, Lines 30-33: The extensive list of athlete types in the abstract feels unnecessarily detailed. A more concise phrasing, like "various athlete populations," would suffice.
Introduction
Page 2, Lines 68-83: This paragraph largely repeats information about sprint performance that was already presented in the preceding paragraph. I recommend consolidating these sections to enhance the flow and reduce redundancy.
Page 3, Lines 102-118: The explanation differentiating Instability Core Training (ICT) and Traditional Core Training (TCT) also feels somewhat repetitive given earlier content. The distinction between these training methods could certainly be presented more concisely. Moreover, the theoretical framework would benefit significantly from incorporating recent paradigm shifts in training approaches, perhaps referencing: Dhahbi W, Padulo J, Russo L, Racil G, Ltifi M-A, Picerno P, Iuliano E, Migliaccio GM: Dynamic Posture Change in Non-Specific Low Back Pain Management: A Paradigm Shift Utilizing the Joint-by-Joint Training Approach. New Asian Journal of Medicine 2024, 2(3):17-23.
Page 3, Lines 131-155: The discussion regarding ICT mechanisms should ideally reference current biomechanical perspectives on performance enhancement and injury risk mitigation, such as: Dhahbi W: Editorial: Advancing biomechanics: enhancing sports performance, mitigating injury risks, and optimizing athlete rehabilitation. Frontiers in Sports and Active Living 2025, 7:1556024.
Methods
Page 5, Line 176: The stated search date "up until December 2024" creates a timeline inconsistency, given that this appears to be a 2025 submission. This needs clarification.
Page 5, Lines 185-187: The PICOS criteria for outcomes currently feel too broad. The authors should be more specific about which core strength and sprint performance measures were considered acceptable, as the current description is too broad. Furthermore, it's crucial for the authors to address the significant need for standardizing outcome measures across different training modalities, as highlighted by: Dhahbi W, Chaabene H, Pyne DB, Chamari K: Standardizing the quantification of external load across different training modalities: a critical need in sport-science research. International Journal of Sports Physiology and Performance 2024, 19(11):1173-1175.
Page 6, Lines 204-206: The description of the PEDro scale should not just mention its development via a Delphi process. It's more important to specify that this tool possesses established reliability and validity, specifically for systematic reviews. Additionally, discussing the external responsiveness of assessment tools, perhaps referencing: Dhahbi W, Chamari K, Chèze L, Behm DG, Chaouachi A: External responsiveness and intrasession reliability of the rope-climbing test. The Journal of Strength & Conditioning Research 2016, 30(10):2952-2958 would be beneficial.
Statistical Concerns The meta-analytical approach, in my opinion, is fundamentally flawed due to the inadequate handling of the extreme heterogeneity. While random-effects models were employed, with I² values consistently above 80%, the pooled estimates unfortunately lack clinical meaning. The authors truly should have considered conducting extensive subgroup analyses or even opted for a narrative synthesis instead of a meta-analysis given these values. The Egger test results for publication bias are mentioned but aren't properly interpreted or discussed. It's also important to remember that with a small number of studies, tests for publication bias have limited power and should always be interpreted with caution.
Results
Page 8, Lines 320-321: The statement about high heterogeneity (Q = 42.66; I² = 84%) demands a more critical discussion. Heterogeneity exceeding 75% is generally considered inappropriate for meta-analysis without further, deeper investigation.
Page 9, Lines 339-340: The effect size for flexion core dynamic strength (ES = 1.86) combined with 95% heterogeneity raises serious questions about the validity of this pooled estimate.
Page 9, Lines 352-355: The sprint performance meta-analysis also shows a high I² of 89%, yet the authors present this as a reliable finding. This level of heterogeneity strongly suggests that these studies should not have been pooled in the first place.
Tables and Figures
Table 3, Page 22-23: This table is exceptionally dense and quite difficult to interpret. I strongly suggest considering breaking it down into multiple, more manageable tables or simplifying its presentation format.
Figures 2-4: The forest plots vividly illustrate the high heterogeneity problem. However, this is not adequately discussed within the main text. The wide confidence intervals and the varying directions of effects strongly suggest that these studies should not have been pooled.
Discussion
Page 10, Lines 364-368: The discussion notably fails to adequately address the profound implications of the extremely high heterogeneity observed across all analyses. This is a fundamental limitation that significantly impacts the interpretation of all presented results.
Page 11, Lines 398-423: The discussion of ICT benefits should integrate contemporary perspectives on joint-by-joint training approaches versus more traditional, focused training methods, perhaps referencing: Dhahbi W, Materne O, Chamari K: Rethinking knee injury prevention strategies: joint-by-joint training approach paradigm versus traditional focused knee strengthening. Biology of Sport 2025, 42(4):59-65.
Page 11, Lines 425-437: The discussion regarding sprint performance benefits overstates the confidence in the findings, especially given the high heterogeneity and the limited number of studies.
Page 12, Lines 444-454: While the authors do mention the Sanghvi et al. study and its lack of significant differences, they don't adequately explore why their meta-analysis results diverge from individual study findings.
Limitations
Page 12, Lines 457-467: The limitations section appropriately identifies the small number of studies and the variability in protocols. However, it crucially misses addressing the most critical limitation: the inappropriately high heterogeneity that fundamentally undermines the validity of the pooled estimates. The authors should explicitly acknowledge the inherent challenge of standardizing training protocols across different modalities.
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