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Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption

Much debate has arisen from research on muscle synergies with respect to both limb impedance control and energy consumption. Studies of limb impedance control in the context of reaching movements and postural tasks have produced divergent findings, and this study explores whether the use of synergie...

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Autores principales: Inouye, Joshua M., Valero-Cuevas, Francisco J.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Public Library of Science 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4750997/
https://www.ncbi.nlm.nih.gov/pubmed/26867014
http://dx.doi.org/10.1371/journal.pcbi.1004737
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author Inouye, Joshua M.
Valero-Cuevas, Francisco J.
author_facet Inouye, Joshua M.
Valero-Cuevas, Francisco J.
author_sort Inouye, Joshua M.
collection PubMed
description Much debate has arisen from research on muscle synergies with respect to both limb impedance control and energy consumption. Studies of limb impedance control in the context of reaching movements and postural tasks have produced divergent findings, and this study explores whether the use of synergies by the central nervous system (CNS) can resolve these findings and also provide insights on mechanisms of energy consumption. In this study, we phrase these debates at the conceptual level of interactions between neural degrees of freedom and tasks constraints. This allows us to examine the ability of experimentally-observed synergies—correlated muscle activations—to control both energy consumption and the stiffness component of limb endpoint impedance. In our nominal 6-muscle planar arm model, muscle synergies and the desired size, shape, and orientation of endpoint stiffness ellipses, are expressed as linear constraints that define the set of feasible muscle activation patterns. Quadratic programming allows us to predict whether and how energy consumption can be minimized throughout the workspace of the limb given those linear constraints. We show that the presence of synergies drastically decreases the ability of the CNS to vary the properties of the endpoint stiffness and can even preclude the ability to minimize energy. Furthermore, the capacity to minimize energy consumption—when available—can be greatly affected by arm posture. Our computational approach helps reconcile divergent findings and conclusions about task-specific regulation of endpoint stiffness and energy consumption in the context of synergies. But more generally, these results provide further evidence that the benefits and disadvantages of muscle synergies go hand-in-hand with the structure of feasible muscle activation patterns afforded by the mechanics of the limb and task constraints. These insights will help design experiments to elucidate the interplay between synergies and the mechanisms of learning, plasticity, versatility and pathology in neuromuscular systems.
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spelling pubmed-47509972016-02-26 Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption Inouye, Joshua M. Valero-Cuevas, Francisco J. PLoS Comput Biol Research Article Much debate has arisen from research on muscle synergies with respect to both limb impedance control and energy consumption. Studies of limb impedance control in the context of reaching movements and postural tasks have produced divergent findings, and this study explores whether the use of synergies by the central nervous system (CNS) can resolve these findings and also provide insights on mechanisms of energy consumption. In this study, we phrase these debates at the conceptual level of interactions between neural degrees of freedom and tasks constraints. This allows us to examine the ability of experimentally-observed synergies—correlated muscle activations—to control both energy consumption and the stiffness component of limb endpoint impedance. In our nominal 6-muscle planar arm model, muscle synergies and the desired size, shape, and orientation of endpoint stiffness ellipses, are expressed as linear constraints that define the set of feasible muscle activation patterns. Quadratic programming allows us to predict whether and how energy consumption can be minimized throughout the workspace of the limb given those linear constraints. We show that the presence of synergies drastically decreases the ability of the CNS to vary the properties of the endpoint stiffness and can even preclude the ability to minimize energy. Furthermore, the capacity to minimize energy consumption—when available—can be greatly affected by arm posture. Our computational approach helps reconcile divergent findings and conclusions about task-specific regulation of endpoint stiffness and energy consumption in the context of synergies. But more generally, these results provide further evidence that the benefits and disadvantages of muscle synergies go hand-in-hand with the structure of feasible muscle activation patterns afforded by the mechanics of the limb and task constraints. These insights will help design experiments to elucidate the interplay between synergies and the mechanisms of learning, plasticity, versatility and pathology in neuromuscular systems. Public Library of Science 2016-02-11 /pmc/articles/PMC4750997/ /pubmed/26867014 http://dx.doi.org/10.1371/journal.pcbi.1004737 Text en © 2016 Inouye, Valero-Cuevas http://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/) , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
spellingShingle Research Article
Inouye, Joshua M.
Valero-Cuevas, Francisco J.
Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption
title Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption
title_full Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption
title_fullStr Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption
title_full_unstemmed Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption
title_short Muscle Synergies Heavily Influence the Neural Control of Arm Endpoint Stiffness and Energy Consumption
title_sort muscle synergies heavily influence the neural control of arm endpoint stiffness and energy consumption
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4750997/
https://www.ncbi.nlm.nih.gov/pubmed/26867014
http://dx.doi.org/10.1371/journal.pcbi.1004737
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