Abstract
Muscle wrapping geometry has a major impact on the muscle force as well as the torque onto the joint exerted by this muscle since these torques highly depend on the muscle’s line of action or, in other words, the muscle moment arm. Most common redirection methods focus on two-dimensional motions and optimise path geometry for only one isolated movement, either flexion, abduction or rotation, instead of covering all degrees of freedom (DOFs). Others can only imitate anatomical paths in a small working range or for single joint movements. For biomechanical simulations of sweeping movements like running or throwing, however, a correct representation of muscle paths for a large range of joint configurations is mandatory. We introduce a new computational algorithm for modelling the muscle path in three-dimensional biomechanical simulations, based on a model description of muscles as massless, visco-elastic strands and the assumption that the muscle acts along a continuous path consisting of piecewise straight lines. In the presented approach, anatomical constraints including bones, tendon sheaths and other surrounding tissue are represented by areas the muscle has to pass. We model these redirection constraints as ellipses, allowing the muscle path to move within these areas and along their frictionless, inner edges. We show that – by only adjusting ellipse parameters – we are able to achieve reasonable moment arms for all (DOFs) and for a large range of joint configurations of uniarticular muscles as well as muscles spanning more than one joint – even for complex geometries.
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