An Exploratory Study of the Acute Effects of Football Heading on Postural Control and Corticospinal Inhibition

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Accept after minor

Comments for author File: Comments.pdf

Comments on the Quality of English Language

A minor correction in English improvement is possible

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors examine the acute effects of 10 shots and 10 headers in adult recreational footballers, comparing linear and nonlinear postural-control metrics alongside the TMS cortical silent period (cSP). The main findings are that, after heading, the anterior–posterior Complexity Index (CI-AP) decreases, RMS-AP and COPx shift increase, and cSP lengthens (some effects are marginal or only significant in pairwise tests). On this basis, the authors argue that nonlinear complexity measures may be more sensitive to detecting non-concussive head impacts (NCHI).The content of the article is complete and the results are reliable, but there are still some issues that need to be addressed：

1. The abstract reads unevenly, and the phrase “this exploratory study” is ambiguous—unclear whether it refers to prior work or to the present study. Please revise to make the subject explicit (e.g., “In this exploratory study, we…”).
2. There is duplicated and inconsistent citation formatting in the same sentence: “(Pearce et al., 2015) (Pearce et al., 2025).” Please verify the years and either merge or remove one of them, and ensure consistent style.
3. Although the heading technique was standardized by instruction (forward header, no jump), in practice the first participant used a ball-delivery machine while all others received hand-tossed balls. This likely altered the consistency of incoming speed and angle. How did you monitor and ensure technical consistency across participants? Was neck-muscle activation assessed to account for possible differences in effort?
4. “Kicking” was chosen as a control to match factors other than head impact, yet the experiment used a fixed sequence: baseline → kicking → heading. Could the kicking task itself modify lower-limb proprioception or postural-control strategies and thus interact with the heading condition? Did you consider a more neutral control (e.g., ball-free simulated movement) or analytic adjustments for order effects?
5. Figure 1 is noticeably blurry. Please replace it with a high-resolution image. Also review all figures and tables for consistent formatting (resolution, font sizes, line widths, color scheme) and standardize them across the manuscript.
6. You note that only 13 participants were included for various reasons and frame the study as exploratory. A sensitivity analysis is provided to show detectable effect sizes at this sample size, but it is based on repeated-measures ANOVA and paired t-tests, whereas the actual analysis relies on linear mixed models (LMMs). Please discuss this mismatch—ideally supplement with an LMM-appropriate sensitivity/simulation analysis, or explain the rationale and limits of using ANOVA-based estimates.
7. The study uses several device-specific, multivariate complexity indices (e.g., mMSE-XY). What is their criterion validity relative to the more commonly reported, force-plate–based univariate metrics (e.g., CI-AP) in the academic literature? Can they be directly compared? Please provide supporting references or analyses.
8. The Methods state that participants completed 60 incongruent Stroop trials with spoken responses, but the Results do not report accuracy, reaction times, or any basic compliance measures. Without these, it’s hard to confirm comparable dual-task load. Please report Stroop performance and consider including it as a covariate or manipulation check.
9. Please temper the wording of the findings and provide a fuller account of missing data. Given the relatively high proportion of missingness, specify the reasons (equipment issues, non-compliance, artifacts, etc.), describe the presumed missingness mechanism, and explain how it was handled (complete-case analysis, multiple imputation, sensitivity analyses) and how this might affect the conclusions.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 

The paper investigates whether ten controlled football headers (non-concussive head impacts) produce short-term alterations in postural control and corticospinal inhibition in amateur players. The study uses a within-subject design with three conditions (baseline, kicking, heading), measuring center-of-pressure (COP) parameters and cortical silent period (cSP) via TMS.
Results suggest decreased postural complexity (CI-AP) and increased corticospinal inhibition post-heading, indicating subtle neurophysiological effects of routine heading.

The paper should be accepted after addressing the following issues

1. Consider cross-validating nonlinear COP complexity findings using permutation or bootstrap resampling to confirm robustness against small-sample bias.
2. The paper lacks explicit timing between heading bouts, rest intervals, and post-test measures. Temporal separation is critical to distinguish neural inhibition from fatigue or arousal effects.
3. Including only male players limits generalizability. The Discussion should acknowledge hormonal and anatomical sex differences that modulate impact biomechanics and neuromuscular control.
4. No direct kinematic or accelerometric data (e.g., peak linear/rotational acceleration) were recorded for each header. Without this, the interpretation of “non-concussive” exposure remains speculative.
   Suggest integrating instrumented mouthguards or headband accelerometers in future work.
5. While CI-AP reduction is interpreted via the “loss of complexity” framework, the biological linkage to neural inhibition remains correlative. Clarify whether CSP changes and CI-AP reductions were correlated within participants.
6. The paper would benefit from a schematic summarizing experimental workflow (baseline → kicking → heading → post-tests), including approximate timing and measurement order.
7. Provide rationale for the chosen 10-header exposure; cite epidemiological data linking such frequency to real-match exposure levels.
8. The Discussion should relate acute CI-AP changes to possible microstructural or metabolic alterations reported in recent omics or biomechanical studies.
   Specifically, integrate literature linking subtle biomechanics of head impacts to downstream molecular responses.
9. Clarify inclusion/exclusion criteria (history of concussion, neurological conditions, vestibular disorders).
10. Add a table summarizing mean ± SD and Cohen’s d for all significant and non-significant effects.
11. The manuscript would benefit from integrating some of these recent studies to enhance the mechanistic and translational context:

•    Cai, L., Yan, S., Ouyang, C., Zhang, T., Zhu, J., Chen, L.,... Liu, H. (2023). Muscle synergies in joystick manipulation. Frontiers in Physiology, 14, 1282295. doi: 10.3389/fphys.2023.1282295
•    Chen, Y., Yu, W., Benali, A., Lu, D., Kok, S. Y.,... Wang, R. (2024). Towards Human-like Walking with Biomechanical and Neuromuscular Control Features: Personalized Attachment Point Optimization Method of Cable-Driven Exoskeleton. Frontiers in Aging Neuroscience, 16, 1327397. doi: 10.3389/fnagi.2024.1327397

Comments for author File: Comments.pdf

Author Response

See attached

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

 Repetitive non-concussive head impacts (NCHIs) may 
contribute to long-term neurodegenerative conditions. However, 
objective, multimodal methods for monitoring acute changes in 
brain health biomarkers following NCHIs remain underdeveloped. 
This exploratory study examined the effects of ten kicking and ten 
heading trials related to association football on linear and nonlinear 
measures of postural control, and corticospinal inhibition. Postural 
control was assessed via force platform analysis in dual-stance and 
single-leg protocols, and corticospinal inhibition was measured us
ing transcranial magnetic stimulation with electromyography. 
Large effects of condition were found for anteroposterior postural 
complexity (CI-AP), anteroposterior sway amplitude, mediolateral 
centre of pressure shift and cortical silent period (η2 > 0.14). Pair
wise comparisons revealed large post-heading effects, particularly 
in CI-AP, which decreased significantly relative to baseline (dz = 
0.71, p = .018) and showed a moderate negative effect relative to 
post-kicking (dz = 0.53, p = .069). These findings suggest a possible 
reduction in postural control adaptability following exposure to ten 
NCHIs, consistent with patterns observed in mild traumatic brain 
injury. Whilst confirmatory research with larger samples is war
ranted, nonlinear measures of postural control complexity demon
strate promise as a sensitive biomarker for detecting acute NCHI
related changes.

There are some problems as follows:

1. The discrption of figure 2 and figure 3 should be more clear.
2. Table 2 and table 3 should be presented in figures form, not only in table form.
3. More experiments should be added in the paper.
4. The conclusion should be more clear.
5. The appendix should be moved to the main body.
6. The format of the paper should  be carefully edited to be more beautiful.
7. The contribution of the paper should be enhanced.

Comments on the Quality of English Language

The English is good.

Author Response

See attached

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have completed the revisions to the raised questions very well, and there are no additional modification suggestions here.