ABSTRACT
An emerging approach for determining subject specific tissue loads based on principles of inverse and forward dynamics is the EMG-to-force model (Hof and van den Berg, 1981). In this approach experimental measurements of normalized EMG for each muscle in the model are required together with kinematic data describing the relative joint angle of each joint under investigation. Normalized EMG data is assumed to be a measure of muscle stimulation from which the active state of the muscle (defined as the relative number of formed cross-bridges in the muscle) can be determined using a model of activation dynamics. Regression equations are used to estimate individual muscle-tendon lengths as a function of the relative joint angles for input into the model of contraction dynamics. This approach possesses features of the forward dynamics approach since the instantaneous length of the muscle fibres is determined from integration of the muscle fibre velocity which is itself predicted using the Hill based model of contraction dynamics. The EMG based modelling approach also possesses features of the inverse dynamics approach since estimates of muscle-tendon length based on experimental measurement of relative joint angles are required in order to estimate muscle-tendon forces in the model of contraction dynamics.
