Adjustment of Muscle Mechanics Model Parameters to Simulate Dynamic Contractions in Older Adults

[+] Author and Article Information
Darryl G. Thelen

Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI 53706-1572

J Biomech Eng 125(1), 70-77 (Feb 14, 2003) (8 pages) doi:10.1115/1.1531112 History: Received September 01, 2000; Revised July 01, 2002; Online February 14, 2003
Copyright © 2003 by ASME
Topics: Force , Muscle , Tendons , Torque
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A Hill-type model was used to describe musculo-tendon contraction mechanics. The model consists of a muscle contractile element in series and parallel with elastic elements. (a) A Gaussian curve was used to describe the active force-length relationship of muscle. (b) The muscle force-velocity function was scaled with activation such that the unloaded contraction velocity was reduced during sub-maximal activation. (c) Tendon force was assumed to increase exponentially with strain during an initial toe region, and linearly with strain thereafter.
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Simulated muscle excitations and ankle torques during a rapid isometric contraction (thick lines). The experimental data (thin lines) are a representative tibialis anterior myoelectric signal and ensemble-averaged torque-time curve recorded from young adult males 7.
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Simulated contractions in dorsiflexion (DF) and plantarflexion (PF) in response to unit pulse muscle excitations of 5 ms duration. Model parameters representative of young adults were used. Contractions are prolonged in plantarflexion due to larger tendon length/fiber length ratios in the plantarflexor muscles.
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Simulated torque-angle curves for isometric (thick black lines), 30 deg/s (thick gray lines) and 120 deg/s (thin black lines) isokinetic contractions using model parameters representative of older males. The superimposed points are the mean (error bar=1 SD) torques recorded experimentally from old males during isometric and isokinetic exertions 7.
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Simulated peak ankle torques, normalized to maximal isometric torque, as a function of velocity during isokinetic dorsiflexion and plantarflexion exertions for young (thick lines) and old (thin lines) adults. Superimposed are the mean (error bar=1 SD) normalized torques recorded from healthy young and old adults 7.




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