A Comparison of Denoising Methods in Onset Determination in Medial Gastrocnemius Muscle Activations during Stance

Round 1

Reviewer 1 Report

1.A greater number of subjects would fit better this kind of study

2.Is it unclear if and how subjects’ skin was prepared before the application of the surface EMG electrodes; furthermore, did Authors follow any guideline for the correct position of them?

3. Regarding the choice of reporting only gastrocnemius medialis: Authors wrote that collected more muscles data. Probably it would have been useful to analyze at least one other muscle (for example an antagonist like the anterior tibial) in comparison.

4. In the discussion Authors mentioned the phenomenon of fiber switching into type I especially in gastrocnemius muscle in elders: a reference would be appropriate.

Best regards

Author Response

A greater number of subjects would fit better this kind of study First of all, we thank the reviewers for their insightful comments and have improved the manuscript, as per the suggestions. The suggestions from reviewers were great and will help us design future study. Response: We agree with the reviewer, a larger population with different age groups would have been very useful. We plan on a future study with larger sample size. Is it unclear if and how subjects’ skin was prepared before the application of the surface EMG electrodes; furthermore, did Authors follow any guideline for the correct position of them? Thank you for your comment. We followed the standard skin preparation procedure. At first, we shaved the part of the body to remove hairs, then used sand paper and alcohol wipes to clean the skin surface. Sometimes it is reported to be itchy but, participants were informed about this during their IRB Consent. Regarding the choice of reporting only gastrocnemius medialis: Authors wrote that collected more muscles data. Probably it would have been useful to analyze at least one other muscle (for example an antagonist like the anterior tibial) in comparison. Thank you for this comment. The purpose of our study was to compare effects of denoising methods on muscle onset detections during stance. We plan to consider this suggestion for our future study. In the discussion Authors mentioned the phenomenon of fiber switching into type I especially in gastrocnemius muscle in elders: a reference would be appropriate. Thank you for your comment. We have added the references now. 1. Wilkinson, D.J., M. Piasecki, and P.J. Atherton, The age-related loss of skeletal muscle mass and function: Measurement and physiology of muscle fibre atrophy and muscle fibre loss in humans. Ageing Research Reviews, 2018. 47: p. 123-132. 2. Kramer, I.F., et al., Extensive Type II Muscle Fiber Atrophy in Elderly Female Hip Fracture Patients. The Journals of Gerontology: Series A, 2017. 72(10): p. 1369-1375. 3. Tieland, M., I. Trouwborst, and B.C. Clark, Skeletal muscle performance and ageing. Journal of Cachexia, Sarcopenia and Muscle, 2018. 9(1): p. 3-19.

Reviewer 2 Report

The authors explored four different denoising techniques to determine the onset and cessation events of muscle activity under different conditions. It is interesting that the detection results of onset showed different behavior by denoising methods as well as walking speed. The authors explained the theory and experimental results to classify the pros and cons of various denoising methods and analyzed well. In the below, I listed several questions and comments to further improve the manuscript.

 

1. In figure 3, authors marked onset and cessation by red stars. However, they are hard to see. Please use clearer marks.
2. In figure 5, the authors insisted that they did not find any significant differences among older and younger participants’ muscle activation time for any denoising method. Please try to match with the y-axis scale between the two graphs in figure 5. It seems the activation time of young participants is faster than older.
3. In the section of 2.3.6. Wavelet Denoising, the authors found that a decomposition level of 6 was adequate and would not remove EMG signal artifacts. What is the level and why was level 5 adequate? Please explain them.
4. I agree with one of conclusion in the article that relying on only low pass filtering is not the solution to determine true muscle onset based on results. Then, the authors mentioned that “delayed onset of lower extremity muscle is an indication that the activation is stimulated by a stretch stimulus, rather than central nervous system control. Delay of gastrocnemius action until late terminal stance implies the influence of passive stretch during dorsiflexion.” I could not find that information or arguments in this article. How do you derive the conclusion? Please explain more details or use references to better understand the conclusion.
5. The values, letters, and characters of x-axes and y-axes in all figures are too small which makes it difficult to see. Please enlarge and modify them to be clear.

 

Author Response

The authors explored four different denoising techniques to determine the onset and cessation events of muscle activity under different conditions. It is interesting that the detection results of onset showed different behavior by denoising methods as well as walking speed. The authors explained the theory and experimental results to classify the pros and cons of various denoising methods and analyzed well. In the below, I listed several questions and comments to further improve the manuscript. 1. In figure 3, authors marked onset and cessation by red stars. However, they are hard to see. Please use clearer marks. First of all, we thank the reviewers for their insightful comments and have improved the manuscript, as per the suggestions. The suggestions from reviewers were great and will help us design future study. Response: Thank you for your comments. We have enlarged the figure now for better visibility. 2. In figure 5, the authors insisted that they did not find any significant differences among older and younger participants’ muscle activation time for any denoising method. Please try to match with the y-axis scale between the two graphs in figure 5. It seems the activation time of young participants is faster than older. Response: Thank you for this comment. We agree with the review that activation time of young participants looks faster in the figure, however, we did not find statistical differences. 3. In the section of 2.3.6. Wavelet Denoising, the authors found that a decomposition level of 6 was adequate and would not remove EMG signal artifacts. What is the level and why was level 5 adequate? Please explain them. Response: Thank you for this comment. The RMS of the signal is considered the ground truth of the EMG signal. Since this is common practice to evaluate the onset and cessation points using RMS of EMG signals. We conducted pilot studies for denoising at different level of EMG and further decided for the decomposition level which is most closest to the RMS signals were considered for EMG signal analysis. 4. I agree with one of conclusion in the article that relying on only low pass filtering is not the solution to determine true muscle onset based on results. Then, the authors mentioned that “delayed onset of lower extremity muscle is an indication that the activation is stimulated by a stretch stimulus, rather than central nervous system control. Delay of gastrocnemius action until late terminal stance implies the influence of passive stretch during dorsiflexion.” I could not find that information or arguments in this article. How do you derive the conclusion? Please explain more details or use references to better understand the conclusion. Response: Thank you for the comment. We have cited the book below (page 152) Barnes, W.P., Feedback and Motor Control in Invertebrates and Vertebrates. 2012: Springer Netherlands. (Page 152) 5. The values, letters, and characters of x-axes and y-axes in all figures are too small which makes it difficult to see. Please enlarge and modify them to be clear. Response: We have Stretched the figures to improve clarity.

Round 2

Reviewer 1 Report

 

The paper has good readability. Further studies including more enrolled subjects will be useful.

Best Regards

 

Reviewer 2 Report

The authors thoroughly addressed all the comments and questions raised by this reviewer. The revised manuscript looks in a good shape to be published in this journal.