Detecting Early-stage Muscle Fatigue to Improve Assist-as-Needed Control Strategies for Active Orthoses

Detecting Early-stage Muscle Fatigue to Improve Assist-as-Needed Control Strategies for Active Orthoses | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Detecting Early-stage Muscle Fatigue to Improve Assist-as-Needed Control Strategies for Active Orthoses Thekla Stefanou, Axel Schneider This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6236620/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Muscle fatigue affects motor neuron function and, in turn, the electromyography\,(EMG) signals used to control wearable technologies. By accounting for this, we can more accurately regulate movement assistance. Muscle fatigue has been widely studied in the fields of sports science, rehabilitation, and occupational health. However, there are contradictory findings in the literature, and some aspects of muscle fatigue mechanisms are not yet well understood. Furthermore, none of the literature found focuses on the detection of early-stage muscle fatigue. Results: In this paper we specifically focus on early-stage muscle fatigue and show that the spectral variance ( \((S_{var})\) ) of the EMG signal is a more reliable measure of fatigue across participants and contraction levels compared to other widely used features. We then make recommendations on how these findings can be used in EMG-controlled assist-as-needed technologies. Experiments were carried out with 16 participants who performed intermittent isometric contractions of the biceps brachii at 20\,%, 50\,% and 75\,% MVC. The reliability of the motor unit action potential conduction velocity (CV) and the median/mean power frequencies (MDPF/MNPF) as measures of fatigue was tested. CV exhibited some linear correlation with perceived fatigue only at the higher contraction levels, for the majority of participants (R2= \((0.18\pm0.23)\) ). Conclusions: CV was found to be an unreliable measure for muscle fatigue and no relationship was found between MDPF/MNPF and fatigue. However, for all participants and contraction levels, the fatigue- \((S_{var})\) relationship could be characterized using a Gaussian model\,(R2= \((0.87\pm0.12)\) ). muscle fatigue electromyography isometric contractions frequency analysis conduction velocity biceps brachii. wearable technologies Full Text Additional Declarations No competing interests reported. Supplementary Files supplementaryplots.pdf Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6236620","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":434307159,"identity":"d7b584fe-1752-44f3-8c6d-12b7eee3b504","order_by":0,"name":"Thekla Stefanou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAUlEQVRIie3PsWrDMBCA4TMCZVHpKnBIXkHFY0L9KicM8ZI0nUKGbgF3MZ3zGN5KtwuCTE6yGrIE8gKGQJdCWwkyFax27KB/ETr4OAkgFPqHpQ0wONkTIDq5wUCBAALeTbi0BAF0CUy5QfJnguJKdGUJeEm8MgqfANPeKro8Lk3+ervbECzG3aS/zRC3kAphWLyuzext/YAE+4nnYdOEkENUyjnFN4WZVY1QFBXGQ+YXwk9Lhmf2YUmuDrUjX74tDHXhtjDutqCiqSPkIZNE6RepyzrjI1Hnd1Vj/4L7zEOys2zfx2nv2bCjWI6G6rAzbbu47yTX5I87/gZCoVAo5O0b5uNSxSU1tckAAAAASUVORK5CYII=","orcid":"","institution":"Hochschule Bielefeld","correspondingAuthor":true,"prefix":"","firstName":"Thekla","middleName":"","lastName":"Stefanou","suffix":""},{"id":434307160,"identity":"2c9ae6c0-87c2-4510-889e-77302be7d897","order_by":1,"name":"Axel Schneider","email":"","orcid":"","institution":"Hochschule Bielefeld","correspondingAuthor":false,"prefix":"","firstName":"Axel","middleName":"","lastName":"Schneider","suffix":""}],"badges":[],"createdAt":"2025-03-16 08:53:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6236620/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6236620/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":90084738,"identity":"d5608db1-e5d3-47e6-9850-f0059ba5b881","added_by":"auto","created_at":"2025-08-28 09:47:23","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5739278,"visible":true,"origin":"","legend":"","description":"","filename":"EarlystageMuscleFatique.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6236620/v1_covered_97c102e7-ef5b-4fb3-b502-179a2b87cc9b.pdf"},{"id":79579378,"identity":"0b36eb9c-9928-4693-b01d-5eb07f11dc2d","added_by":"auto","created_at":"2025-03-31 11:40:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1412979,"visible":true,"origin":"","legend":"","description":"","filename":"supplementaryplots.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6236620/v1/d54ef822c5a2850612e5bcae.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Detecting Early-stage Muscle Fatigue to Improve Assist-as-Needed Control Strategies for Active Orthoses","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"muscle fatigue, electromyography, isometric contractions, frequency analysis, conduction velocity, biceps brachii. wearable technologies","lastPublishedDoi":"10.21203/rs.3.rs-6236620/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6236620/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground:\u003c/h2\u003e\u003cp\u003eMuscle fatigue affects motor neuron function and, in turn, the electromyography\\,(EMG) signals used to control wearable technologies. By accounting for this, we can more accurately regulate movement assistance. Muscle fatigue has been widely studied in the fields of sports science, rehabilitation, and occupational health. However, there are contradictory findings in the literature, and some aspects of muscle fatigue mechanisms are not yet well understood. Furthermore, none of the literature found focuses on the detection of early-stage muscle fatigue.\u003c/p\u003e\u003ch2\u003eResults:\u003c/h2\u003e\u003cp\u003eIn this paper we specifically focus on early-stage muscle fatigue and show that the spectral variance (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((S_{var})\\)\u003c/span\u003e\u003c/span\u003e) of the EMG signal is a more reliable measure of fatigue across participants and contraction levels compared to other widely used features. We then make recommendations on how these findings can be used in EMG-controlled assist-as-needed technologies. Experiments were carried out with 16 participants who performed intermittent isometric contractions of the biceps brachii at 20\\,%, 50\\,% and 75\\,% MVC. The reliability of the motor unit action potential conduction velocity (CV) and the median/mean power frequencies (MDPF/MNPF) as measures of fatigue was tested. CV exhibited some linear correlation with perceived fatigue only at the higher contraction levels, for the majority of participants (R2=\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((0.18\\pm0.23)\\)\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e\u003ch2\u003eConclusions:\u003c/h2\u003e\u003cp\u003eCV was found to be an unreliable measure for muscle fatigue and no relationship was found between MDPF/MNPF and fatigue. However, for all participants and contraction levels, the fatigue-\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((S_{var})\\)\u003c/span\u003e\u003c/span\u003e relationship could be characterized using a Gaussian model\\,(R2=\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((0.87\\pm0.12)\\)\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e","manuscriptTitle":"Detecting Early-stage Muscle Fatigue to Improve Assist-as-Needed Control Strategies for Active Orthoses","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-31 11:32:24","doi":"10.21203/rs.3.rs-6236620/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"44afc111-2e33-4d04-bcfc-d8fe4d2db413","owner":[],"postedDate":"March 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-28T09:39:08+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-31 11:32:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6236620","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6236620","identity":"rs-6236620","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}