Dissociation of Gravity and Limb Dynamics in Motor Control

Dissociation of Gravity and Limb Dynamics in Motor Control | 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 Article Dissociation of Gravity and Limb Dynamics in Motor Control Valeriya Gritsenko, Tjasa Kunavar, Marko Jamsek, Olivier White, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9215277/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 Human movements remain accurate and stable despite changes in external forces, yet it is unclear how the nervous system separates and compensates for gravitational loads and intrinsic limb dynamics when generating motor commands. This question is difficult to address under terrestrial conditions, where these forces are inherently coupled. Here we dissociated gravitational acceleration from limb dynamics using parabolic flight. Nine participants performed visually guided pointing movements during alternating microgravity (0g), normogravity (1g), and hypergravity (2g), while upper-limb kinematics and shoulder muscle activity were recorded. Inverse-dynamics analysis revealed that the gravity-independent dynamic component of muscle torques remained largely invariant across gravitational conditions, whereas gravity-related torques scaled proportionally with gravitational acceleration. In contrast, muscle activation exhibited systematic gravity-dependent modulation in both agonist and antagonist muscles, including increased co-contraction consistent with elevated shoulder stiffness. Critically, the dynamic component of EMG-derived torques increased with gravitational load despite minimal changes in the corresponding mechanical torques, particularly during movement deceleration. This dissociation indicates that muscle activity is not solely determined by inverse-dynamics requirements but reflects additional control objectives. A regression-based reconstruction showed that muscle activation patterns can be predicted from a compact set of biomechanical variables, primarily gravity-related torque and movement velocity. Together, these findings demonstrate that motor commands combine predictive compensation for gravitational and inertial forces with gravity-dependent modulation of limb impedance. Scaling joint stiffness with gravitational load provides a robust control strategy for stabilizing movement under variable mechanical conditions. This principle offers a biologically grounded framework for the design of adaptive controllers in prosthetics, wearable robotics, and rehabilitation systems operating in uncertain environments. Biological sciences/Neuroscience/Motor control Biological sciences/Neuroscience/Computational neuroscience Full Text Additional Declarations Yes there is potential Competing Interest. V. Gritsenko has financial interests in a start-up Neurowired that develops biomedical technology; she is a co-founder and Managing Partner of the company. Neurowired provided financial support for travel of VG to scientific conferences. Supplementary Files Supplementaryinformation.pdf Supplementary Information 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. 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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-9215277","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":620357782,"identity":"87456204-074d-4c0d-a7c5-4851bc057574","order_by":0,"name":"Valeriya Gritsenko","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIiWNgGAWjYJCCAyBCgoH5AEMCTIiHkJYDYC1sCcRrYYBo4TFAiODTYnB+7cPDH/7Y5Em293zd8LCNIXHDjQTGB2/b8Gi58dzgwMG2tGJpnrPbbiScAWthNpyLR4vkjGMMBw42HE6cJ5EL1FLBkDtzRgKbNC8hLQf+/AdqyXl2I8EArIX9Nz4t/PxtQC1sBxJnS+SwgW3pl0hgY8arRYKN4cDZtuTEmT3HzIB+kajv53nYLDnnHG4tbPzHmD9U/LFLnHG8+dnNn202xmzsyQc/vCnDrYVBIgGVC8SMDXjUg1x2AL/8KBgFo2AUjAIGAJU5WgymLJhWAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-6408-9433","institution":"West Virginia University","correspondingAuthor":true,"prefix":"","firstName":"Valeriya","middleName":"","lastName":"Gritsenko","suffix":""},{"id":620357783,"identity":"9fcbd3cc-8471-4fae-8eab-dd1009fdf9d3","order_by":1,"name":"Tjasa Kunavar","email":"","orcid":"","institution":"Jožef Stefan Institute","correspondingAuthor":false,"prefix":"","firstName":"Tjasa","middleName":"","lastName":"Kunavar","suffix":""},{"id":620357784,"identity":"419b0b6f-bd6b-41f8-bde3-3a2010b80c1e","order_by":2,"name":"Marko Jamsek","email":"","orcid":"","institution":"Jožef Stefan Institute","correspondingAuthor":false,"prefix":"","firstName":"Marko","middleName":"","lastName":"Jamsek","suffix":""},{"id":620357785,"identity":"35376ec3-babd-431f-b0f1-b268d9d704f8","order_by":3,"name":"Olivier White","email":"","orcid":"","institution":"Université Bourgogne Europe, INSERM","correspondingAuthor":false,"prefix":"","firstName":"Olivier","middleName":"","lastName":"White","suffix":""},{"id":620357786,"identity":"fde1ad6a-01d6-4526-9692-024c714f82a2","order_by":4,"name":"Jan Babič","email":"","orcid":"","institution":"Jožef Stefan Institute","correspondingAuthor":false,"prefix":"","firstName":"Jan","middleName":"","lastName":"Babič","suffix":""}],"badges":[],"createdAt":"2026-03-24 18:25:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9215277/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9215277/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108493447,"identity":"1d5844fe-bb72-4833-806e-7535ca983d92","added_by":"auto","created_at":"2026-05-05 10:00:24","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1189191,"visible":true,"origin":"","legend":"","description":"","filename":"Parabolicflightfinal.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9215277/v1_covered_b551889c-5293-4919-8fcb-6627e572041c.pdf"},{"id":108406070,"identity":"7e587149-231b-4ec5-81b8-3dc71a449ee5","added_by":"auto","created_at":"2026-05-04 09:41:17","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":605772,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"Supplementaryinformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9215277/v1/2f4d795e7339fa4f3b6b4024.pdf"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nV. 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This question is difficult to address under terrestrial conditions, where these forces are inherently coupled.\u003c/p\u003e\n\u003cp\u003eHere we dissociated gravitational acceleration from limb dynamics using parabolic flight. Nine participants performed visually guided pointing movements during alternating microgravity (0g), normogravity (1g), and hypergravity (2g), while upper-limb kinematics and shoulder muscle activity were recorded. Inverse-dynamics analysis revealed that the gravity-independent dynamic component of muscle torques remained largely invariant across gravitational conditions, whereas gravity-related torques scaled proportionally with gravitational acceleration. 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