Design of a mathematical model of force in whole skeletal muscle

We are developing a mathematical model of force production in whole skeletal muscle using independent models of muscle fascicles and connective tissue (tendon and aponeurosis). The model was based upon Zajac's (1990) basic three-element design: active and passive elements for the fascicles and a single passive element for the combined tendon and aponeurosis. The data used for this model were recently collected from cat soleus and covered the entire physiological range of motion (ROM), including both shortening and lengthening velocities. Novel features of this model include a short-range passive force resisting compression, a new normalization constant for connective tissue lengths to replace the potentially troublesome slack length, and a new length dependent term for lengthening velocities in the force-velocity relationship. Both previously published and new equations were compared to determine the "best-fit" equation for each of the functions in the model.