MECHANICS OF FELINE SOLEUS .2. DESIGN AND VALIDATION OF A MATHEMATICAL-MODEL

We have developed a mathematical model to describe force production in cat soleus during steady-state activation over a range of fascicle le ngths and velocities. The model was based primarily upon a three eleme nt design by Zajac but also considered the many different features pre sent in other previously described models. We compared quantitatively the usefulness of these features and putative relationships to account for a set of force and length data from cat soleus whole-muscle descr ibed in a companion paper. Among the novel features that proved useful were the inclusion of a short-length passive force resisting compress ion, a new normalisation constant for connective-tissue lengths to rep lace the potentially troublesome slack length, and a new length depend ent term for lengthening velocities in the force-velocity relationship . Each feature of this model was chosen to provide the most accurate d escription of the data possible without adding unneeded complexity. Pr eviously described functions were compared with novel functions to det ermine the best description of the experimental data for each of the e lements in the model.