Identifying differences in gait adaptability across various speeds using movement synergy analysis

David Ó’Reilly; Peter Federolf

doi:10.1371/journal.pone.0244582

Peer Review History

Original SubmissionJuly 29, 2020
23 Oct 2020 Decision Letter - Fabio A. Barbieri, Editor PONE-D-20-23630 Identifying differences in gait adaptability across various speeds using movement synergy analysis PLOS ONE Dear Dr. Oreilly, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. ============================== Dear authors, The manuscript had positive revisions. However, minor revisions are necessary yet. Please address them. ============================== Please submit your revised manuscript by Dec 07 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. Please include the following items when submitting your revised manuscript: A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols We look forward to receiving your revised manuscript. Kind regards, Fabio A. Barbieri, PhD Academic Editor PLOS ONE Journal Requirements: When submitting your revision, we need you to address these additional requirements. 1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf 2. Please amend your list of authors on the manuscript to ensure that each author is linked to an affiliation. Authors’ affiliations should reflect the institution where the work was done (if authors moved subsequently, you can also list the new affiliation stating “current affiliation:….” as necessary). [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Yes Reviewer #2: Partly ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 3. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #1: Yes Reviewer #2: Yes ****** 4. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: Yes Reviewer #2: Yes ****** 5. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: This study evaluates a novel approach to represent the size of neuromuscular control the PAkRMS with respect to co-ordination variability and arm swing. hypothesis clearly stated. Detailed description of what was done. clearly presented results Good discussion, well done very interesting and relevant. Reviewer #2: Dear Mr. O’Reilly, I thoroughly enjoyed reading your manuscript titled, “Identifying differences in gait adaptability across various speeds using movement synergy analysis.” I believe that it presents a helpful contribution to the fields of gait analysis and postural adaptability, and it fits well within the scope and publication criteria of this journal. I also found it to be very well written, I appreciate your style and your ability to speak both generally and specifically within this computationally intense method. I do recommend some minor revisions, some of which are merely text-level revisions, which I will detail by section below. Abstract -There are many abbreviations in the abstract, some of which could be minimized. PA4RMS and PA6RMS, for example, would have little meaning to someone who reads only the abstract, and they confused me on first read. I would recommend writing in more general terms, e.g., “The principal movement component relating to push-off was identified…” (line 29). Introduction -Line 89, bodys center of mass is missing an apostrophe. -Line 109 says “specific phases gait…,” it appears to be missing a preposition. Methods -Line 196, Equation 2. Your outcome of interest here is deviation phase, not CRP. I would recommend using Equation 2 to define DP. You can include CRP within your definition or do a two-line definition like you did with NJI, e.g., DP=std(CRP(t))=std(φ_proximal (t)- φ_distal (t)) -In the statistical analysis section I think you do an excellent job providing rationale for the regression model that you selected. -Lines 217-218, overall, I enjoy the innovative method of dimensionality reduction in kinematic data to look at whole-body adaptation strategies within these principal movements. I think it does a good job summarizing the high-dimensional data that biomechanists tend to distill down into a joint-by-joint and plane-by-plane analysis of point data. However, I wonder if it may be too soon to connect a derived metric like PAkRMS with the concept of neuromuscular control. It is a strong topic of debate whether the synergies derived from EMG in muscle synergy analysis represent any true aspect of neuromuscular control (1,2). Kinematics are a step further removed from this discussion, because you there are no neuromuscular signals being measured. This could be indicative of behavior, and perhaps with further research it could be validated as an indirect measure of neuromuscular control. Nevertheless, I believe it may be too soon to draw the connection at the moment. Results -Line 260 says mid-sing rather than mid-swing. -Figure 1/Section 3.1.1. I have a few questions regarding the extracted principal movements: -Should the variance explained total to 100%? The first 2 PM’s alone add to 101.1% and PMs 1-7 total 109.74%. -PM’s 5-7 each account for <1% of the variance. Other dimensionality reduction techniques typically use a cutoff or other criterion for the number of principal components that likely contribute meaningfully to the patterns of behavior observed. One could argue that retaining and drawing conclusions from the highest order components would be akin to fitting noise. The results go on to implement these PMs into statistical models and even identify PA6RMS as the best fit model of the DP x NJI relationship. Has the use of this method to explain direct contributions of the highest order components to movement patterns been validated? Do the eigenvectors provide insights about whether these components should remain? -In Figure 1’s caption, it is noted that “an amplification factor of 2 was used to provide clarity to more subtle movements.” How did you go about deciding which movements to amplify? Is it possible that, per the comments above, movements that were too subtle to detect without amplification might not warrant inclusion within these results? -In Table 4, it would be more consistent with the rest of the manuscript if Equation 5 said DP x NJI, rather than DP x Jerk. Discussion -No comments. Works Cited in Methods Comment 1. Alessandro C, Delis I, Nori F, Panzeri S, Berret B. Muscle synergies in neuroscience and robotics: from input-space to task-space perspectives. Front Comput Neurosci [Internet]. 2013 [cited 2020 Oct 19];7. Available from: http://journal.frontiersin.org/article/10.3389/fncom.2013.00043/abstract 2. Zelik KE, La Scaleia V, Ivanenko YP, Lacquaniti F. Can modular strategies simplify neural control of multidirectional human locomotion? J Neurophysiol. 2014 Jan 1. 2014;111:1686–702. ****** 6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No Reviewer #2: Yes:** Caitlin L Banks [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. 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Revision 1
26 Oct 2020 Author Response Dear Editor, I am writing to you in response to the recent revision given to the manuscript “Identifying differences in gait adaptability using movement synergy analysis”. Firstly, I would like to thank you for the timely response and the service you provide. As advised, consideration has been made further to formatting this manuscript towards the requirements of the Plos One journal. These formatting changes include headings font, author affiliations, reference style and figures among others. The following is the authors response to both reviewers: Reviewer 1 Thank you for taking the time to review this manuscript. I appreciate the kind words regarding the writing style. This is indeed encouraging for future work. Reviewer 2 From the outset, thank you for taking the time to review this manuscript and we’re glad you enjoyed reading it. Both authors have read the points raised and find them valid and also find that they will ultimately improve the manuscript. You can find a response to each point you have made below: “Abstract -There are many abbreviations in the abstract, some of which could be minimized. PA4RMS and PA6RMS, for example, would have little meaning to someone who reads only the abstract, and they confused me on first read. I would recommend writing in more general terms, e.g., “The principal movement component relating to push-off was identified…” (line 29).” The authors agree with this and have amended the abstract by adding a quick description of both PA4RMS and P6RMS as the push off mechanism and Right – Left side weight transfer respectively, thus offering a more interpretable quick read. “Introduction -Line 89, bodys center of mass is missing an apostrophe. -Line 109 says “specific phases gait…,” it appears to be missing a preposition.” The authors agree with this and thank the reviewer for their consideration. Both lines have been amended accordingly in the new manuscript version. “Methods -Line 196, Equation 2. Your outcome of interest here is deviation phase, not CRP. I would recommend using Equation 2 to define DP. You can include CRP within your definition or do a two-line definition like you did with NJI, e.g., DP=std(CRP(t))=std(φ_proximal (t)- φ_distal (t)) -In the statistical analysis section I think you do an excellent job providing rationale for the regression model that you selected.” The authors agree with the above point made. The calculation of Deviation phase has now been presented in the manuscript as advised. “-Lines 217-218, overall, I enjoy the innovative method of dimensionality reduction in kinematic data to look at whole-body adaptation strategies within these principal movements. I think it does a good job summarizing the high-dimensional data that biomechanists tend to distill down into a joint-by-joint and plane-by-plane analysis of point data. However, I wonder if it may be too soon to connect a derived metric like PAkRMS with the concept of neuromuscular control. It is a strong topic of debate whether the synergies derived from EMG in muscle synergy analysis represent any true aspect of neuromuscular control (1,2). Kinematics are a step further removed from this discussion, because you there are no neuromuscular signals being measured. This could be indicative of behavior, and perhaps with further research it could be validated as an indirect measure of neuromuscular control. Nevertheless, I believe it may be too soon to draw the connection at the moment.” Thank you for this comment. The authors understand the concern raised but have chosen to continue with the use of neuromuscular control in the revised version. This decision was made based on the following considerations: - Kinematic synergies in this manuscript merely represent correlated changes in marker positions (as specified in line 119) and therefore do not infer the origin of neuromuscular control. The PAk variable captures accelerations in the marker coordinates that behave in a synergistic fashion. As muscles which are activated by the nervous system pull body segments to cause movement it is reasonable to describe these variables in terms of neuromuscular control. Such synergies are similar to that of M-modes in the literature (Krishnamoorthy et al., 2003). The following article goes into detail on the PAk variable and what it captures while also using this terminology (Longo et al., 2019). - The authors believe that the paragraph (line 97 – 108) may cause some confusion with readers in regards to what the PAk variable captures and therefore have added the following statement, “Synergies have been successfully identified in not just the muscular space but also in dynamic and kinematic spaces (Federolf, 2016; Grinyagin et al., 2005). It must be noted however that the origin of these synergies and whether they represent an input or output of neuromuscular control is still a point of debate in the literature (Bizzi and Cheung, 2013; Tresch and Jarc, 2009). Nonetheless identifying deficits in adaptability across specific phases of gait from a dynamic systems perspective has the potential to inform targeted rehabilitation interventions and clinical assessments (Federolf et al., 2014).”… We hope this encapsulates the current position of the research on this topic while the explanation of what a kinematic synergy is at line 119 ensures the reader understands that it is a reflection of synergistic behaviour rather than an inference of neural origin. - The authors have also attempted further clarification in the introduction with the following addition from line 124 – 126: “As muscles activated by the nervous system causes changes in body segment motion, variables computed from PAk time-series have been of focus in related literature as the extracted acceleration signals represent the actions of the neuromuscular system on body segments (Haid et al., 2018; Longo et al., 2019; Promsri et al., 2020; Zago et al., 2019).” “Results -Line 260 says mid-sing rather than mid-swing.” The authors have made adjustments accordingly. “-Figure 1/Section 3.1.1. I have a few questions regarding the extracted principal movements: -Should the variance explained total to 100%? The first 2 PM’s alone add to 101.1% and PMs 1-7 total 109.74%.” This figure has been adjusted with the correct variance explained. The 7 principal components now sum to 97.8% of total variance. “-PM’s 5-7 each account for <1% of the variance. Other dimensionality reduction techniques typically use a cutoff or other criterion for the number of principal components that likely contribute meaningfully to the patterns of behavior observed. One could argue that retaining and drawing conclusions from the highest order components would be akin to fitting noise. The results go on to implement these PMs into statistical models and even identify PA6RMS as the best fit model of the DP x NJI relationship. Has the use of this method to explain direct contributions of the highest order components to movement patterns been validated? Do the eigenvectors provide insights about whether these components should remain?” This is a very valid remark made by the reviewer. The authors however would like to point the reviewer to lines 170 – 171 where a cross-validation on the principal components derived is detailed and a cut-off of 15 degrees is described. From this cross-validation, the first 7 components did not significantly change when a subject was left out of the analysis, indicating that the components although capturing a small % of variance are robust across subjects. This cross-validation protocol has been carried out in the following paper also (Haid et al., 2018). “-In Figure 1’s caption, it is noted that “an amplification factor of 2 was used to provide clarity to more subtle movements.” How did you go about deciding which movements to amplify? Is it possible that, per the comments above, movements that were too subtle to detect without amplification might not warrant inclusion within these results?” The use of an amplification factor in this study was simply for interpretation purposes during analysis and visualizations in the graph. No amplification factor was implemented on variables used in the statistical analysis. For a brief on how this amplification factor is implemented please see the following references (Federolf, 2016; Haid et al., 2019). The authors recognize the concern raised regarding the use of higher order principal components however the above responses should address this. “-In Table 4, it would be more consistent with the rest of the manuscript if Equation 5 said DP x NJI, rather than DP x Jerk.” The authors have made the terminology more consistent across the manuscript and thank the reviewer. References Federolf, P.A., 2016. A novel approach to study human posture control: “Principal movements” obtained from a principal component analysis of kinematic marker data. Journal of Biomechanics 49, 364–370. https://doi.org/10.1016/j.jbiomech.2015.12.030 Haid, T.H., Doix, A.-C.M., Nigg, B.M., Federolf, P.A., 2018. Age effects in postural control analyzed via a principal component analysis of kinematic data and interpreted in relation to predictions of the optimal feedback control theory. Frontiers in aging neuroscience 10, 22. Haid, T.H., Zago, M., Promsri, A., Doix, A.-C.M., Federolf, P.A., 2019. PManalyzer: A software facilitating the study of sensorimotor control of whole-body movements. Frontiers in neuroinformatics 13, 24. Krishnamoorthy, V., Latash, M.L., Scholz, J.P., Zatsiorsky, V.M., 2003. Muscle synergies during shifts of the center of pressure by standing persons. Experimental Brain Research 152, 281–292. https://doi.org/10.1007/s00221-003-1574-6 Longo, A., Haid, T., Meulenbroek, R., Federolf, P., 2019. Biomechanics in posture space: Properties and relevance of principal accelerations for characterizing movement control. Journal of Biomechanics 82, 397–403. Attachments Attachment Submitted filename: Response to reviewers.docx https://doi.org/10.1371/journal.pone.0244582.r002
20 Nov 2020 Decision Letter - Fabio A. Barbieri, Editor PONE-D-20-23630R1 Identifying differences in gait adaptability across various speeds using movement synergy analysis PLOS ONE Dear Dr. Oreilly, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. ============================== Dear authors, One reviewer has indicated minor revisions for your manuscript. The reviewer indicated two specific points that I suggest that you addressed adequately, please. ============================== Please submit your revised manuscript by Jan 04 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. Please include the following items when submitting your revised manuscript: A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols We look forward to receiving your revised manuscript. Kind regards, Fabio A. Barbieri, PhD Academic Editor PLOS ONE [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation. Reviewer #2: (No Response) ******** 2. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #2: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #2: Yes ****** 4. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #2: Yes ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #2: Yes ****** 6. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #2: I appreciate that the authors provided a timely resubmission which acknowledged each comment from the first round of review. There are two points that I would like to discuss further. In lines 119-123 of the introduction, the authors have modified some content to clarify the work that has been done that leads them to conclude the PAk time series represent actions of the neuromuscular system. After reviewing the string of self-citations provided in the manuscript body and the response to reviewers, I cannot conclude whether the field would either agree or disagree with the characterization of PAk as representative of neuromuscular control. I do not wish to stand in the way of good work being published due to a disagreement on the language used to describe a metric. However, it would be my preference that the authors would blend the first and second submission versions of line 121, to keep the more reserved tone and state “…as the extracted acceleration signals are thought to represent the actions of the neuromuscular system on body segments,” as this more adequately reflects the stance of the authors in the comments to the reviewers. Regarding the robustness of components across subjects in the methods section lines 163-164, I will acknowledge that I am not used to seeing a cross-validation of this type be the deciding factor in how many principal components get retained. I do still have reservations about maintaining and later drawing conclusions about the PMs that account for such a small proportion of the variance. If the authors are willing to provide the eigenvalues of the PMs displayed in Figure 1, this would be in keeping with what is done in previous studies using this technique (e.g., Haid et al. 2018, Longo et al. 2019). This way the reader will be provided with an additional piece of information that allows them to judge the contribution of these PMs for themselves. Ultimately, I do conclude that this work is worthy of publication in PLOS One. I have no issues with the remainder of the manuscript. If the authors are willing to provide the eigenvalues noted above then I am willing to accept this manuscript for publication. ****** 7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #2: Yes:** Caitlin Banks [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0244582.r003
Revision 2
20 Nov 2020 Author Response Dear Editor, I am writing in response to the second minor revision of the manuscript entitled “Identifying differences in gait adaptability across various speeds using movement synergy analysis”. Thank you for the timely turn around in revision. I have read the reviewers comments and you may find the responses to both below: Reviewer 2 Thank you for your careful consideration of this manuscript and for the quick turnaround in reviewing it. Having read the comments made, you can find a response to both in the following: “In lines 119-123 of the introduction, the authors have modified some content to clarify the work that has been done that leads them to conclude the PAk time series represent actions of the neuromuscular system. After reviewing the string of self-citations provided in the manuscript body and the response to reviewers, I cannot conclude whether the field would either agree or disagree with the characterization of PAk as representative of neuromuscular control. I do not wish to stand in the way of good work being published due to a disagreement on the language used to describe a metric. However, it would be my preference that the authors would blend the first and second submission versions of line 121, to keep the more reserved tone and state “…as the extracted acceleration signals are thought to represent the actions of the neuromuscular system on body segments,” as this more adequately reflects the stance of the authors in the comments to the reviewers.” In the previously submitted manuscript, the authors made attempts to clarify the definition of the PAk variable noting the current position of the research on muscle synergies and providing a clear description of what this variable is capturing. The authors have also pointed towards previous research using this variable and so wish to stay in line with these studies and their definition used. The authors agree with the amendment recommended by the reviewer and have changed line 121 to the following: “…variables computed from PAk time-series have been of focus in related literature as the extracted acceleration signals are thought to represent the actions of the neuromuscular system on body segments…”. We hope this conveys a more conservative view on the variable to the reader and we again thank the reviewer for their considerations. “Regarding the robustness of components across subjects in the methods section lines 163-164, I will acknowledge that I am not used to seeing a cross-validation of this type be the deciding factor in how many principal components get retained. I do still have reservations about maintaining and later drawing conclusions about the PMs that account for such a small proportion of the variance. If the authors are willing to provide the eigenvalues of the PMs displayed in Figure 1, this would be in keeping with what is done in previous studies using this technique (e.g., Haid et al. 2018, Longo et al. 2019). This way the reader will be provided with an additional piece of information that allows them to judge the contribution of these PMs for themselves.” The authors agree that eigenvalues should be included. We have therefore created another figure (Fig 2.) directly below Figure 1 that illustrates both the percentage of variance explained by each component and the eigenvalues. The reader can thus see that although a cross validation of these components revealed that these components are adequately stable, some indeed explain a very small amount of the variance in the data. Attachments Attachment Submitted filename: Response to reviewer.docx https://doi.org/10.1371/journal.pone.0244582.r004
14 Dec 2020 Decision Letter - Fabio A. Barbieri, Editor Identifying differences in gait adaptability across various speeds using movement synergy analysis PONE-D-20-23630R2 Dear Dr. Oreilly, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org. If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, Fabio A. Barbieri, PhD Academic Editor PLOS ONE Additional Editor Comments (optional): Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation. Reviewer #2: All comments have been addressed ******** 2. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #2: (No Response) ****** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #2: (No Response) ****** 4. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #2: (No Response) ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #2: (No Response) ****** 6. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #2: All comments have been appropriately addressed and I recommend that this manuscript is accepted for publication. ****** 7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #2: Yes:** Caitlin Banks https://doi.org/10.1371/journal.pone.0244582.r005
Formally Accepted
16 Dec 2020 Acceptance Letter - Fabio A. Barbieri, Editor PONE-D-20-23630R2 Identifying differences in gait adaptability across various speeds using movement synergy analysis Dear Dr. Ó' Reilly: I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department. If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org. If we can help with anything else, please email us at plosone@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Fabio A. Barbieri Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0244582.r006

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