EMG to force processing II: Estimation of parameters of the Hill muscle model for the human triceps surae by means of a calfergometer

Abstract

On a calfergometer isotonic contractions were performed by the calf muscles of human subjects. The measured torque M m was compared to the torque M processed from the EMG and the joint angle by means of an electronic processor based on the Hill muscle model. By means of these experiments the model parameters were determined for the torque-angle relation, the torque-angular velocity relation and the parallel elastic component (PEC). Experiments were done (a) for the soleus only (4 subjects) and (b) for the combination of soleus and gastrocnemius (8 subjects). It turned out that: • — the torque-angle parameters varied among subjects; • — the torque-angular velocity parameters for soleus only varied also among subjects; • — for the combined calf muscle group the interindividual differences in the torque-angular velocity parameters could be neglected; • — one of the parameters of the PEC was the same for all subjects, while the other was variable among the subjects. The obtained parameter values are discussed and compared with available literature data. Values for the r.m.s. and the peak error in the isotonic phases of the contraction are given and compared with values predicted from the stochastic properties of the EMG signal.