Understanding muscle coordination of the human leg with dynamical simulations.

Full Abstract

Muscles coordinate multijoint motion by generating forces that cause reaction forces throughout the body. Thus, a muscle can redistribute existing segmental energy by accelerating some segments and decelerating others. In the process, a muscle may also produce or absorb energy, in which case its summed energetic effect on the segments is positive or negative, respectively. This Borelli Lecture shows how dynamical simulations derived from musculoskeletal models reveal muscle-induced segmental energy redistribution and muscle co-functions and synergies. Synergy occurs when co-excited muscles distribute segmental energy differently to execute the motor task. In maximum height jumping, high vertical velocity at lift-off occurs desirably at full body extension because biarticular leg muscles redistribute the energy produced by the uniarticular leg muscles. In pedaling, synergistic ankle plantarflexor force generation during leg extension allows the high energy produced by the uniarticular hip and knee extensors to be delivered to the crank. An analogous less-powerful flexor synergy exists during leg flexion. Hamstrings reduce crank deceleration during the leg extension-to-flexion transition by not only producing energy but delivering it to the crank through its contribution to the tangential (accelerating) crank force, though this hamstrings function occurs at the opposite (flexion-extension) transition when pedaling backwards. In walking, the eccentric quadriceps activity in early stance not only decelerates the leg but also accelerates the trunk. In mid-stance, the uni- and biarticular plantarflexors, by having opposite segmental energetic effects, act in synergy to support the whole body, so segmental potential and kinetic energy exchange can occur. To conclude, the extraction of unmeasurable variables from dynamical simulations emulating task kinematics, kinetics, and EMGs shows how the production of force and energy by individual muscles contribute to the energy flow among the individual segments during task execution.

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Author information

Author/s: Zajac, Felix E (FE);

Affiliation: Rehabilitation R & D Center (153), VA Palo Alto Health Care System, CA 94304, USA. zajac(-atsign-)rrdmail.stanford.edu

Grants: NS17662 (Agency:NINDS NIH HHS)

Journal and publication information

Publication Type: Lectures; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.

Journal: Journal of biomechanics (J Biomech), published in United States. (Language: eng)

Reference: 2002-Aug; vol 35 (issue 8) : pp 1011-8

Dates: Created 2002/07/19; Completed 2003/01/15; Revised 2007/11/14;

PMID: 12126660, status: MEDLINE (last retrieval date: 12/26/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Bicycling - physiology
Computer Simulation
Humans
Lower Extremity - physiology
Models, Biological

Motor Skills - physiology
Movement - physiology
Muscle, Skeletal - physiology
Nonlinear Dynamics
Walking - physiology

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