Soleus H reflex and afferent discharges from antagonist muscles. An electrophysiological method of evaluation.

The influence of electric activation of the peroneal nerve (i.e., of anterior leg muscles) on the ipsilateral soleus H response was studied in normal, parkinsonian, hemiplegic and spastic spinal paraplegic subjects. The anterior muscles were held in a forced extended position to obtain their maximal stretch during isometric contraction. The stimulus evoking soleus H reflex was delivered after a conditioning stimulus to the peroneal nerve at different intervals, between 10 and 500 msec. The excitability curve of the soleus H reflex obtained in this way showed a rather constant pattern in normal subjects, which significantly differed from that of the parkinsonians. "Pyramidal" patients showed a pattern not significantly disimilar from normals. Parkinsonians were characterized by clear facilitation of the soleus H response for intervals (about 100-150 msce) corresponding to the maximum tension increase on the anterior muscles.