Dynamics of the H Reflex and Tonic Activity in the Human m.Soleus at a Voluntary Movement of the Upper Limb

In tests on healthy volunteers, we examined the effects of voluntary flexion of the elbow joint on the magnitude of the H reflex recorded from the ipsilateral m. soleus and on tonic EMG activity of this muscle. The H reflex was subjected to two-phase modulation; a period of facilitation lasting up to 300 msec was replaced by subsequent long-lasting inhibition. Tonic EMG-activity of the m. soleus induced by moderate voluntary contraction of its antagonist did not undergo significant changes under these conditions. As is supposed, changes in the intensity of background presynaptic inhibition exerted on afferents of the H reflex arc are the reason for the observed shifts in the magnitude of this reflex.