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Computational and Mathematical Methods in Medicine
Volume 2012 (2012), Article ID 848630, 13 pages
http://dx.doi.org/10.1155/2012/848630
Research Article

Spreading out Muscle Mass within a Hill-Type Model: A Computer Simulation Study

1Institut für Sport-und Bewegungswissenschaft, Universität Stuttgart, Allmandring 28, 70569 Stuttgart, Germany
2Lehrstuhl für Bewegungswissenschaft, Institut für Sportwissenschaft, Friedrich-Schiller-Universität, Seidelstraße 20, 07749 Jena, Germany
3Stuttgart Research Centre for Simulation Technology, Pfaffenwaldring 7a, 70569 Stuttgart, Germany
4Institut für Mechanik (Bauwesen), Universität Stuttgart, Lehrstuhl II, Pfaffenwaldring 7a, 70569 Stuttgart, Germany

Received 24 February 2012; Accepted 27 August 2012

Academic Editor: Hendrik Schmidt

Copyright © 2012 Michael Günther et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

It is state of the art that muscle contraction dynamics is adequately described by a hyperbolic relation between muscle force and contraction velocity (Hill relation), thereby neglecting muscle internal mass inertia (first-order dynamics). Accordingly, the vast majority of modelling approaches also neglect muscle internal inertia. Assuming that such first-order contraction dynamics yet interacts with muscle internal mass distribution, this study investigates two questions: (i) what is the time scale on which the muscle responds to a force step? (ii) How does this response scale with muscle design parameters? Thereto, we simulated accelerated contractions of alternating sequences of Hill-type contractile elements and point masses. We found that in a typical small muscle the force levels off after about 0.2 ms, contraction velocity after about 0.5 ms. In an upscaled version representing bigger mammals' muscles, the force levels off after about 20 ms, and the theoretically expected maximum contraction velocity is not reached. We conclude (i) that it may be indispensable to introduce second-order contributions into muscle models to understand high-frequency muscle responses, particularly in bigger muscles. Additionally, (ii) constructing more elaborate measuring devices seems to be worthwhile to distinguish viscoelastic and inertia properties in rapid contractile responses of muscles.