Extracting low-velocity concentric and eccentric dynamic muscle properties from isometric contraction experiments.
Determining dynamic properties of mammalian muscles, such as activation characteristics or the force-velocity relation, challenges the experimentalist. Tracking system, apparatus stiffness, load oscillation, force transducer, other sensors, and additional measuring devices may be incorporated, integrated and evaluated in an experimental set-up. In contrast, isometric contraction experiments (ICEs) are less challenging, but are generally not considered to reveal dynamic muscle properties. Yet, a sensitivity analysis of our muscle model discloses the influence of concentric, eccentric and activation parameters on isometric force development. Accordingly, we used solely experimental ICE data to identify muscle model parameters that generally describe concentric as well as eccentric muscle performance. In addition, we compared two different activation dynamics in regards to their physiological relevance to improve model-fits to ICE data. To this end, we optimized different combinations of such dynamic parameter subsets with respect to their influence on contraction solutions. Depending on muscle length in our optimized model, the contractile element reached shortening peaks during activation in the range 9-39% of its maximum contraction velocity, and about 8-25% during lengthening when deactivated. As a first result, we suggest one formulation of activation dynamics to be superior. Second, the step in slope of the force-velocity relation at isometric force was found to be the least influential among all dynamic parameters. Third, we suggest a specially designed isometric experimental set-up to estimate this transition parameter. Fourth, because of an inconsistency in literature, we developed a simple method to determine switching times of the neural stimulation and thus electro-mechanical delay (EMD) values from measuring muscle force in ICEs only.
Mathematisches Institut, Universität Koblenz, Universitätsstr. 1, Koblenz 56070, Germany. Electronic address: rrockenfeller@uni-koblenz.de.
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Rockenfeller
Institut für Sport- und Bewegungswissenschaft, Universität Stuttgart, Human Movement Simulation Lab, Allmandring 28, Stuttgart 70569, Germany; Institut für Sportwissenschaft, Friedrich-Schiller-Universität, Lehrstuhl für Bewegungswissenschaft, Seidelstraße 20, Jena 07749, Germany.
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Günther
D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology*; D007537:Isometric Contraction / Q000502:physiology*; D008962:Models, Theoretical; D018482:Muscle, Skeletal / Q000502:physiology*
Biomechanical optimization; Electro-mechanical delay; Experimental design; Sensitivity analysis; Striated muscle model