Analytical Approach for Evlauation of the Sensitivity of a Hill Based Muscle Model

Component based Hill muscle models are commonly used in musculoskeletal models to predict muscle forces (Zajac, 1989) and have been recommended as the most practical and accurate approach for simulating human movement(van den Bogert et al., 1998; Winters et al., 1987). Hill based models can take several forms, each component of the model representing the properties of one or more tissues in the musculo-tendenous unit. A simple Hill model (Figure 1), can include three common elements. The contractile element (CE) models active muscle force and takes into account the force-length (FL) and force-velocity (FV) muscle properties. The series elastic element (SE) models the stretch in the tendon, aponeurosis, and other soft tissue during loading, while the parallel elastic element (PE) models the passive properties of the muscle fibers. In many studies, the PE is ignored, often considered irrelevant when modelling physiological movements(Winters, 1990). In other models, pennation angle or viscous elements of the muscle are considered – while some models include these components in the WIDTH parameter of the FL relationship of the CE (Gerritsen, 1997).