Comparison between two muscle models under dynamic conditions

One fundamental problem when trying to calculate the force developed by one muscle during a motor task is the muscle model. Usually, one control signal is juxtaposed to one musclotendon unit. The question is how is this signal connected to the activation of the motor units (MUs) that compose the muscle and fire differently. The aim of the paper is to compare a Hill-type muscle model to a model composed of MUs. A fast elbow flexion performed by only one muscle is considered. The activation necessary for performing the motion and the corresponding frequencies are calculated for cases of fast and slow muscles using Hill-type model. Then the muscle is modelled as a mixture of 774MUs with uniformly distributed twitch parameters. Using MotCo software the moments of impulsation of all MUs and their mechanical responses are predicted. The activation characteristics obtained by the two muscle models are compared. It is concluded that there are two essential parameters for proper muscle modelling: the lead-time and the MUs composition.