Hill muscle model performance during natural activation and electrical stimulation

This study assessed the ability of the Hill model to predict muscle force for both electrically stimulated and naturally activated cat soleus muscle. Our results indicate that Hill model errors increase with increases in muscle velocity and decrease with increases in motor unit firing rates. For a given muscle velocity, errors were largest in for the range of firing frequencies most relevant for naturally activated muscle. During large muscle displacements, average Hill model errors often were greater than 100%.