A comparative analysis of co-contraction indices using synthetic EMG data: Implications for selection and interpretation

Hannah D. Carey; Friedl De Groote; Andrew Sawers

doi:10.1371/journal.pone.0343081

Peer Review History

Original SubmissionJanuary 31, 2026
22 Apr 2026 Decision Letter - Andrea Tigrini, Editor -->PONE-D-26-05502-->-->A comparative analysis of co-contraction indices using synthetic EMG data: Implications for selection and interpretation-->-->PLOS One Dear Dr. Sawers, 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. ============================== ACADEMIC EDITOR: The manuscript presents a well-written and comprehensive review of muscle co-contraction indexes. However, please update it by addressing all the concerns raised by the reviewers. ============================== Please submit your revised manuscript by Jun 06 2026 11:59PM. 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If your research concerns only data provided within your submission, please write "All data are in the manuscript and/or supporting information files" as your Data Availability Statement. 4. We note that the grant information you provided in the ‘Funding Information’ and ‘Financial Disclosure’ sections do not match. When you resubmit, please ensure that you provide the correct grant numbers for the awards you received for your study in the ‘Funding Information’ section. 5. Thank you for stating the following financial disclosure: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Research reported in this publication was supported by the Department of Defense under Award No. HT9425-24-1-0212. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Department of Defense. Please state what role the funders took in the study. 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Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. Additional Editor Comments : The manuscript presents a well-written and comprehensive review of muscle co-contraction indexes. However, please update it by addressing all the concerns raised by the reviewers. [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 ******** -->2. Has the statistical analysis been performed appropriately and rigorously? --> Reviewer #1: N/A ****** -->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 ****** -->4. 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While the normalization parameters are mentioned in the manuscript and the script used to generate the synthetic EMG signal is available in the GitHub repository, the intermediate steps that lead from those parameters to the plot shown in Figure 9 are not entirely clear from the text. It would therefore be helpful if the authors could briefly clarify the processing steps that transform the reported normalization parameters into the final signal representation shown in the figure. ****** -->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? 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Revision 1
7 May 2026 Author Response Manuscript PONE-D-26-05502 Response to Reviewers Dear Dr. Tigrini, Thank you for the opportunity to address reviewer and editorial comments. We have provided the point-by-point response below. All tracked changes are noted as red underlined text for additions/changes, and red strikethrough text for deletions. Editor’s Comments to Authors: 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 Response: We have reviewed the style template and revised the manuscript as appropriate. 2. Please note that PLOS One has specific guidelines on code sharing for submissions in which author-generated code underpins the findings in the manuscript. In these cases, we expect all author-generated code to be made available without restrictions upon publication of the work. Please review our guidelines at https://journals.plos.org/plosone/s/materials-and-software-sharing#loc-sharing-code and ensure that your code is shared in a way that follows best practice and facilitates reproducibility and reuse. Response: We have made all code available without restriction on GitHub, archived with Zenodo. 3. Please provide a complete Data Availability Statement in the submission form, ensuring you include all necessary access information or a reason for why you are unable to make your data freely accessible. If your research concerns only data provided within your submission, please write "All data are in the manuscript and/or supporting information files" as your Data Availability Statement. Response: All data are in the manuscript and/or supporting information files. 4. We note that the grant information you provided in the ‘Funding Information’ and ‘Financial Disclosure’ sections do not match. When you resubmit, please ensure that you provide the correct grant numbers for the awards you received for your study in the ‘Funding Information’ section. Response: We have revised the grant information to match in the ‘Funding Information’ and ‘Financial Disclosure’ sections. The correct grant number is included in the ‘Funding Information’ section. 5. Thank you for stating the following financial disclosure: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Research reported in this publication was supported by the Department of Defense under Award No. HT9425-24-1-0212. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Department of Defense. Please state what role the funders took in the study. If the funders had no role, please state: "The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript." If this statement is not correct you must amend it as needed. Please include this amended Role of Funder statement in your cover letter; we will change the online submission form on your behalf. Response: Thank you. The funder had not role. We have included the requested statement in our cover letter. 6. If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. Response: N/A 7. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. Response: We have checked the reference list, which is complete. We have updated the formatting for consistency between items (i.e., abbreviation of journals). We have also added two references regarding the color palettes used in manuscript figures, reproduced below: 62. Crameri F. Scientific colour maps. Zenodo; 2023. doi:10.5281/zenodo.8409685 63. Crameri F, Shephard GE, Heron PJ. The misuse of colour in science communication. Nat Commun. 2020;11: 5444. doi:10.1038/s41467-020-19160-7 Additional Editor Comments: The manuscript presents a well-written and comprehensive review of muscle co-contraction indexes. However, please update it by addressing all the concerns raised by the reviewers. Response: Thank you for your feedback. We have included our response to the reviewer below. Reviewer’s Comments to Authors: Reviewer 1 The manuscript is well written and the methodological framework is carefully developed. The comparison of multiple co-contraction indices is particularly interesting and represents a valuable methodological contribution. I only have a minor suggestion regarding Figure 9. While the normalization parameters are mentioned in the manuscript and the script used to generate the synthetic EMG signal is available in the GitHub repository, the intermediate steps that lead from those parameters to the plot shown in Figure 9 are not entirely clear from the text. It would therefore be helpful if the authors could briefly clarify the processing steps that transform the reported normalization parameters into the final signal representation shown in the figure. Response: Thank you for your review. There are no processing steps as this is synthetic EMG. We simply used 0.6, 1.0, and 1.4 as the maximum height of a linear function (with zero intercept) to create the dotted, dash-dotted, and dashed lines in Figure 9. Bar plots on the left represent the co-contraction index calculated from the solid line vs each dash/dot line. We have updated the caption of figure 9 (excerpt below) to clarify. Revised Text: Figure 9. Amplitude normalization influences each CCI in distinct ways. In panels A and B, the amplitude of EMG1 (solid black lines) is fixed, while that of EMG2 varies to represent three amplitude normalization conditions: non-normalized (dotted line, maximum amplitude 1.4), within-task normalization (dash-dotted line, maximum amplitude 1), and MVC normalization (dashed line, maximum amplitude 0.6). Panels C and D show bar plots of co-contraction values for all six CCIs, calculated from the three EMG1 and EMG2 combinations in panels A and B. Amplitude-driven CCIs (i.e., Rudolph and Unnithan-Frost) are most affected when amplitude normalization reduces both EMGlow and total EMG (panel C). In contrast, shaped-based CCIs, like Falconer-Winter, are most sensitive when normalization alters only one of EMGlow and total EMG (panel D). Abbreviations: CCISR: simple ratio; CCIFW: Falconer-Winter; CCITS: Thoroughman-Shadmehr; CCIR: Rudolph; CCIUF: Unnithan-Frost; CCIT: temporal. Attachments Attachment Submitted filename: CCI paper response to reviewers.docx https://doi.org/10.1371/journal.pone.0343081.r002
12 May 2026 Decision Letter - Andrea Tigrini, Editor A comparative analysis of co-contraction indices using synthetic EMG data: Implications for selection and interpretation PONE-D-26-05502R1 Dear Dr. Sawers, 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 will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support. 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, Andrea Tigrini, Ph.D. Academic Editor PLOS One Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0343081.r003
Formally Accepted
Acceptance Letter - Andrea Tigrini, Editor PONE-D-26-05502R1 PLOS One Dear Dr. Sawers, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS One. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, 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. You will receive an invoice from PLOS for your publication fee after your manuscript has reached the completed accept phase. If you receive an email requesting payment before acceptance or for any other service, this may be a phishing scheme. Learn how to identify phishing emails and protect your accounts at https://explore.plos.org/phishing. If we can help with anything else, please email us at customercare@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. Andrea Tigrini Academic Editor PLOS One https://doi.org/10.1371/journal.pone.0343081.r004

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