The Existence of Shared Muscle Synergies Underlying Perturbed and Unperturbed Gait Depends on Walking Speed

Round 1

Reviewer 1 Report

Good article and a work that is a continuation from other researches. The methodological way of presenting the steps for the analysis of the results from EMG results of the 12 healthy subjects is very thorough and it shows the organized work of the writers.

This article is well written, organized correctly and provides results that indicate that shared muscle synergies underlying perturbed and unperturbed walking are less present for slow walking than for fast walking. The main objective of the article is to make significant remarks for the muscle synergies via the EMG signals (eight muscles per leg, was measured and decomposed into muscle 18 synergies and weighting curves using non-negative matrix factorization). Introduction and Materials and Methods parts are reasonable given the premise of the paper. The Results part is analyzed and explained with the appropriate number of tables and figures. The structure in Discussion and Conclusion are well argued and the benefits of the methodology are obvious and successful. Moreover, the results the results are as expected.

The paper aims to investigate the existence of a shared set of muscle synergies underlying balance responses assessed in a group of healthy subjects. The performance of the methodology is accurate and fulfill the requirements of the start hypothesis in the results.

Author Response

Dear reviewer,

 

First of all, we would like to thank you for your careful review and kind words.

 

We have revised the manuscript to accommodate all suggestions in order to improve the quality of the manuscript. All changes have been highlighted in the copy with the changes-tracked and in the clean copy of the revised document (Changes_Tracked_Highlighted and Clean_Highlighted). Changes highlighted in green and blue are according to the other reviewers' suggestions. We also provide a final non-highlighted clean copy (Clean). 

 

Yours sincerely,

Lotte Hagedoorn and co-authors.

Reviewer 2 Report

This paper deals with the identification of shared muscle synergies during gait in perturbed or unperturbed conditions, when different walking speeds are selected. The Authors refer to a previous work [7], in which they carried out a similar analysis by focusing on the selection of balance recovery actions. In the previous paper, the study was performed mainly by a biomechanical point of view (e.g., by considering spatio-temporal parameters). In the current work, the focus is given to muscle synergy through surface EMG analyses. 
The article is generally well written and fits the journal, however there are some concerns related to the novelty of the research and its significance, as compared to the previous work cited by the Authors. They should try to improve the communication of the main findings of the new study, for instance by deepening the discussion of the results and explaining how they relate to the current state of the art. For this purpose, the implementation of such a particular experimental setup, based on the BART device, might represent a relevant aspect that deserves to be further highlighted. 

In the following, some specific questions and observations are reported.

1. L29-30: Please provide some reference for this sentence.
2. L56-59: The Authors might explain here what they assess as outward or inward directed perturbations. They could provide same reference to Figure 1, that clarifies this aspect.
3. L70-74: The Authors refer to the frontal plane in the Abstract or Introduction section, although they seem to refer to perturbations applied in the transverse (horizontal) plane. Please check on this.
4. L85-91: How did the brace secured subject from falling? The possible existence of a minimal loading condition at the pelvis might affect the spontaneity of the motion, thus providing a pre-conditioning of the postural control system. This might have an impact on the significance of the results.
5. L105-106: Where does the pelvic manipulator apply the perturbation? The percentage of subject weight corresponds to the total force applied in the medio-lateral direction by the manipulator? Please provide some indications about the accuracy and repeatability of the perturbations provided by the system, in terms of amplitude and duration.
6. L106-107: The Authors considered only the outcomes of the analysis for the 10% perturbation amplitude. However, the results might depend on the magnitude of the perturbation, due to nonlinearities associated to the behavior of postural control system, and not only on the onset of the stimuli. Please comment on this.
7. L147-149: The Authors refer to M as a set of measured data, then as the muscle activation. I suggest to choose a single definition to avoid ambiguous interpretation of the methodology. This applies also to W matrix.
8. Equation 3: Please, clarify the usage of matrices M and WC and vectors M_k and WC_k.
9. L172: Please introduce VAF_overall before it is used in the text.
10. L188-189: The Author should provide a justification for choosing only the left aligned conditions.
11. Figure 2: Each plot title highlights the selected speed, therefore transparency might be unnecessary for the plot on the left.
12. L236-246: This part, related to the definition of the muscle synergies U1...U4, should belong to the Materials and Methods section. In general, a revision of the Results section is recommended, in order to improve the readability and conciseness of the paper. Any discussion about the results should be moved to the next section.

Author Response

Dear reviewer,

 

First of all, we would like to thank you for your careful review, kind words and insightful comments. Please see the attachment for the point-by-point response to your comments. 

 

We have revised the manuscript to accommodate all suggestions in order to improve the quality of the manuscript. Please find attached the new version of the manuscript entitled “The existence of shared muscle synergies underlying perturbed and unperturbed gait depends on walking speed”. All changes have been highlighted in the copy with the changes-tracked and in the clean copy of the revised document (ChangesTracked_Highlighted and Clean_Highlighted). Changes highlighted in green are according to your suggestions, changes highlighted in blue are according to the other reviewers’ suggestions. We also provide a final non-highlighted clean copy (Clean). 

 

Yours sincerely,

Lotte Hagedoorn and co-authors.

Author Response File: Author Response.pdf

Reviewer 3 Report

Muscle synergy theory assumes that the central nervous system generates a wide range 9 of complex motor outputs by recruiting muscle synergies with different strengths and timings. The 10 current understanding is that a common set of muscle synergies underlies unperturbed as well as 11 perturbed walking at self-selected speeds. The aim of this study was to investigate whether a shared set of 13 muscle synergies underlined balance recovery responses following inward and outward directed 14 perturbations in the frontal plane at various perturbation onsets and walking speeds.

General comments:

• Please ask a native English speaker to check your manuscript.
• Please write with italic the parameters in text in Figures and in equations.

Special comments:

• Abstract: please provide the investigated muscles
• Introduction: please summarize the lack of the previous research
• Experimental procedure: please provide in inclusion and exclusion criteria
• Conclusion: please provide exactly the novum of the present study

Author Response

Dear reviewer,

 

First of all, we would like to thank you for your careful review and insightful comments. Please see the attachment for the point-by-point response to your comments. 

 

We have revised the manuscript to accommodate all suggestions in order to improve the quality of the manuscript. Please find attached the new version of the manuscript entitled “The existence of shared muscle synergies underlying perturbed and unperturbed gait depends on walking speed”. All changes have been highlighted in the copy with the changes-tracked and in the clean copy of the revised document (ChangesTracked_Highlighted and Clean_Highlighted). Changes highlighted in blue are according to your suggestions, changes highlighted in green are according to the other reviewers’ suggestions. We also provide a final non-highlighted clean copy (Clean). 

 

Yours sincerely,

Lotte Hagedoorn and co-authors.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

After a english editing I recommend the acceptance