Structural and control mechanisms for generating force and power from whole muscles

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Muscle models that enable accurate and reliable assessment of in vivo motor function, rigorously tested in animal and human studies, have broad application to human health and life-long mobility. Recent models of muscle force production show that we still have much to learn about how whole muscles generate force during daily activities. The long-term goal of this research program is to translate the complex mechanisms of muscle recruitment and structural interactions into refined muscle models that can predict in vivo function more accurately. Identifying the mechanisms that contribute to whole-muscle function will enhance our ability to study and maintain human health and mobility. The results from this work will have direct application to computational representations of muscles during analysis of movement, and will be utilized by biomechanists, biomedical engineers and health professionals.*** The 3D paths of muscle fibres, their interactions with surrounding connective tissue and the forces produced by the whole muscle are all affected by the way in which the fibres bulge during contraction. We will investigate the causal mechanisms, and the consequences of, the transverse bulging of the fibres. During daily activities, only a fraction of the muscle fibres are activated during each contraction. Recent evidence showed how the presence of inactive fibres affects the contractile properties of whole muscle; we will test whether this is due to the dynamic properties of this inactive tissue. The mechanics of a limb depends on the interaction and coordination of all the muscles in the limb. We will test the effect of muscle coordination on efficiency during cycling. This research program will have an impact on Natural Sciences and Engineering through the development of new tools and technologies, and through our novel scientific findings. We will (1) develop novel ultrasound-based imaging techniques to quantify fascicle bulging in 3D during voluntary contraction, (2) develop and validate 3D finite element models of contracting muscle with both experimentally measured forces, and the internal 3D geometry of the muscle fibres, and (3) develop a feed-back system that allows muscle coordination to be changed in real-time. These new tools will be applied to address novel scientific questions about (A) the effect of muscle structure on whole-muscle function, (B) the role of the dynamics of inactive tissue in the whole muscle, and (C) mechanisms relating muscle coordination to the mechanical output of the leg. *****