Establishing Reference Data for Electromyographic Activity in Gait: Age and Gender Variations
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript is well-written. The results are interesting and meaningful to other work. I have a few comments to make the manuscript more comprehensive and accurate as well as easier to follow:
- The age and gender were investigated as key factors of difference in EMG data. What about height/leg length, weight or BMI? There might be a weak correlation between all these factors. In the discussion, it is suggested to establish clinical EMG reference for age and gender future study investigate gender and age without mentioning other factors. I think the results in this study are not enough to suggest age and gender to be the only clinical guidelines without considering other factors. It is suggested to explain to provide rational or add additional analysis to have comprehensive results.
- It would be helpful to add a figure demonstrating the location of each muscle and an example of what the raw data looks like per muscle per gait cycle. There should be a sequence of how each muscle was fired and that can be helpful to be used to explain the gait cycle segmentation/signal processing.
- Did you remove the first and last few gait cycles for the 15-m walkway? It should be specified if the reference range is concluded with or without these transition cycles.
- How much data is outside the reference range or confidence interval? I think it is important to present those results and discuss possible reasons.
- It would be also interesting to see the variance of each gait cycle within each subject to see if there is a difference or does it fit into the reference range.
- Either in the introduction or discussion, the broader impacts of having EMG references should be added. What is your vision of how these references being used by other research or applications? Saying being clinical guidance is not enough.
- I think a distribution of age should be provided as a figure in addition to Table 1, to give more details about the age factor.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
After critically reviewing your manuscript entitled "Establishing Reference Data for Electromyographic Activity in Gait: Age and Gender Variations," I would like to congratulate you on your excellent work. This study makes a valuable contribution to clinical biomechanics by investigating differences in electromyographic (EMG) activation during gait as a function of age and gender while using a modern statistical approach such as Statistical Parametric Mapping (SPM). The sample size appears adequate, and the justification for the need for normative data sets stratified by age and sex is well founded.
However, I have identified methodological limitations and gaps in the presentation and interpretation of results that should be improved before the manuscript is ready for publication. Below, I present my observations, highlight key issues, and suggest necessary revisions to improve the rigor and clarity of the study.
1. METHODOLOGY AND STUDY DESIGN
1.1. You initially mention 108 participants divided into three age groups but opted to exclude the “juvenile” group (13–18 years old) due to a small sample size (n = 11), leaving only 97 participants (children <13 years; adults >18 years). While this decision is statistically justifiable, completely omitting this intermediate age group creates a gap in understanding motor and muscular development during adolescence. I recommend performing an exploratory analysis to assess whether this group aligns more closely with adults or children. If this is not feasible, I suggest explicitly discussing the implications of this exclusion in the Discussion section (and providing a stronger justification for this decision).
1.2. The manuscript states that before 2013/14, EMG data were recorded using Biovision, whereas later, Delsys (and Myon 320) were used. Different systems may have distinct pre-amplification gains, hardware filters, and signal noise levels, affecting the amplitude and shape of the EMG signal. However, you do not clarify whether any cross-calibration process was conducted to ensure signal comparability. Please provide a methodological justification regarding data compatibility or, preferably, conduct a comparative analysis to confirm that findings were not influenced by technological variations. At the very least, discuss how these differences were statistically handled (e.g., additional normalizations, agreement tests).
1.3. While self-selected speed is commonly used in observational studies, gait speed can significantly affect EMG signal amplitude and shape. The literature suggests that speed directly impacts EMG amplitude, which could be an alternative explanation for some of the observed differences between children and adults. I recommend checking whether significant differences in speed exist between groups and, if they do, consider performing statistical adjustments to control for this bias. If this analysis is not feasible, a more in-depth discussion of this limitation should be included.
1.4. You describe filtering procedures (Butterworth 20–350 Hz band-pass, 9 Hz cutoff for the envelope) and normalization (based on the mean signal). However, I would appreciate further clarification on the choice of normalization method. For inter-subject and inter-group comparisons, some studies opt for normalization based on maximal voluntary isometric contraction (MVIC) or peak dynamic activation within the gait cycle. If I understood correctly, you used the mean signal. Please explain the rationale for this choice and discuss potential implications for the study’s results.
1.5. Your study primarily discusses kinematic and kinetic parameters in the sagittal plane. However, gender differences may also be observed in the coronal and transverse planes. While I understand that the focus of your article is electromyographic activity, I recommend briefly discussing why your analysis was limited to the sagittal plane. Providing this justification would enhance methodological transparency.
2. RESULTS STRUCTURE AND FIGURE CLARITY
2.1. The EMG envelopes and statistical significance intervals are well constructed, but the description of gait cycle periods where significant differences occur could be clearer. Currently, these time windows are scattered throughout the text and figures. I strongly suggest that a summary table be created that highlights the specific gait cycle phases in which differences were observed. At the very least, I recommend highlighting the precise phase boundaries within the figure captions.
2.2. The use of SPM allows for full time series analysis and you identify specific differences within the gait cycle. I recommend discussing whether these differences occur only at peak moments or are more widespread. Is there increased activity throughout the stance phase or are the differences concentrated in shorter time intervals? In addition, you suggest in some sections that significant differences occur within narrow time windows. A more detailed discussion of the clinical implications of these findings would strengthen their practical relevance.
2.3. While you present your findings, there is no explicit comparison with previous studies that have examined EMG activation patterns during gait. Including such a comparison would contextualize your findings. I suggest briefly discussing how your values compare to references such as Schwartz et al. (2008) and Di Nardo et al. (2015).
2.4. The recommendation to include age and sex in normative databases is valid and well supported. However, the link between your findings and clinical practice and rehabilitation should be made more explicit. If possible, please provide concrete clinical examples of how your data can assist in personalized motor rehabilitation programs.
3. DISCUSSION AND CONSISTENCY WITH THE LITERATURE
3.1. Your primary comparison is between children and adults, excluding adolescents. Although you briefly mention this as a limitation, I recommend expanding this discussion.
3.2. You discuss increased coactivation in children and stronger push-off forces in adults. However, I suggest incorporating neurophysiological (or biomechanical) explanations to support these findings, referencing classic studies on nervous system maturation and motor strategy development.
3.3. You mention a statistical power analysis, concluding that at least 47 participants (with 12 per subgroup) were needed to detect interactions. I suggest reinforcing how this calculation translates to clinical practice—for instance, if a rehabilitation clinic wants to establish its normative database, this information could help estimate the required sample size. Making this point more practical would significantly enhance the discussion.
4. CONCLUSIONS, LIMITATIONS, AND FINAL RECOMMENDATIONS
4.1. Your conclusions accurately reflect the results of the study, but two statements need to be rephrased:
4.1.1. You claim that the results are "robust" because the sample includes 97 participants and the statistical power was sufficient to detect age × sex interactions. However, this robustness does not necessarily apply to all comparisons in the study. I recommend refining this statement to be more specific.
4.1.2. The conclusion does not explicitly mention certain important methodological limitations, such as the exclusion of the adolescent group and the lack of control for gait speed. I recommend adding a final paragraph highlighting these points and suggesting future studies to address them.
Based on the above observations, I recommend a major revision. Your study has scientific merit and relevance, but methodological limitations and presentation gaps need to be addressed before publication.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe purpose of this study, to provide normative EMG gait data based on age and gender, was achieved. The authors showed a need for this research. More information is needed in the methods section. Several word choice and word tense errors were identified and need to be corrected. The results, discussion, and conclusion were consistent with the primary purpose of the study. Tables and figures complemented the text. Errors in the references were noted. See pdf for detailed comments and questions.
Comments for author File: Comments.pdf
Minor word choice and tense errors were noted.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for Authorsplease see my comment attached
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I sincerely appreciate your efforts in revising the manuscript and incorporating the suggested changes. The improvements in methodological clarity, the justification for the exclusion of the adolescent group, and a more structured discussion of the results have significantly improved the rigor of the second version of the manuscript. Your study remains a valuable contribution to clinical biomechanics, particularly in establishing normative electromyographic (EMG) data for gait analysis while accounting for age and gender differences.
While the second version of your manuscript is significantly improved, some minor but critical refinements are still needed to improve methodological transparency, structure, and interpretability. Below, I provide specific comments that I believe will further strengthen the study.
1. You provided a more explicit justification for the exclusion of the juvenile group, stating that the sample size was too small for statistical analysis. Although this rationale is valid, it would be helpful to include a brief discussion on the potential impact of this exclusion on the interpretation of age-related differences in EMG activation. Adolescence is a period of significant neuromuscular development, and the absence of data from this group may create a gap in understanding muscle activation transitions from childhood to adulthood.
2. You have added an important methodological improvement by explicitly stating that a quality check was performed to compare data between Biovision and Delsys/Myon 320 EMG Systems. However, in my opinion, a summary of the quality check results (e.g., whether statistical tests confirmed the absence of systematic differences) would add further credibility to this methodological adjustment.
3. While you now acknowledge that speed can influence EMG signals, it remains unclear whether gait speed was significantly different between age groups. If speed data were collected, I suggest a statistical comparison between children and adults should be included. If speed differed significantly, it would be ideal to perform an ANCOVA or other statistical adjustments to control for this variable. If this analysis is not feasible, the limitation should be discussed more explicitly.
4. You clarified that mean signal normalization was used rather than peak dynamic activation or maximal voluntary isometric contraction (MVIC). However, I recommend briefly discussing the potential limitations of this normalization approach in inter-group comparisons, particularly in studies comparing younger and older individuals with different muscle strengths.
5. You provide a reasonable justification for why the study primarily analyzed sagittal plane kinematics and kinetics. Although the analysis focuses on sagittal movement, it would be beneficial to acknowledge the clinical relevance of coronal and transverse plane deviations in conditions like gait asymmetrical or neuromuscular disorders.
6. You have now included a detailed power analysis confirming that 47 participants (with at least 12 per subgroup) are sufficient to detect age × sex interactions. If possible, the practical application of this power analysis could be further explained (e.g. by discussing how future gait laboratories or rehabilitation clinics could use this information to establish their reference datasets).
7. You mention greater semimembranosus activity at initial contact in adults and greater hamstring activation in midstance in children. I suggest that you briefly link these findings to motor control development, proprioceptive maturation, or biomechanical adaptations, which would provide a more comprehensive neurophysiological explanation.
8. You have improved the discussion by referencing studies such as Schwartz et al. (2008) and Di Nardo et al. (2015). If possible, it would be useful to include a direct numerical comparison of the study's EMG values with those from previous research. Another point, if available, is that providing a real-world example of how these data could be used in rehabilitation, clinical diagnostics, or sports performance assessment would increase the practical impact of the study.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThank you for addressing the initial comments/questions/suggestions; highlighting the changes really helped me in this review. However, there are several remaining word choice and word tense errors. In addition, I found a couple of instances where sentence clarification is needed. See pdf for specifics.
Comments for author File: Comments.pdf
many minor errors remain.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
