Spinal inhibition in man: depression of the soleus H reflex by stimulation of the nerve to the antagonist muscle.

A period of inhibition of the soleus H reflex, called D1 inhibition, follows stimulation of the nerve to the antagonist muscles, the peroneal nerve, in normal man. The results confirm earlier descriptions of D1 and show an intracord latency of approximately 4-5 msec and a reduction of the H reflex by about 60%. D1 reaches its maximum 15-20 msec after stimulation and its duration is more than 30 msec. Effective stimuli were volleys of two to five pulses given as 10 msec duration bursts at a strength of 1.2 motor thresholds. Cutaneous afferents were ineffective and the possibility that D1 is mediated by low threshold muscle afferents is discussed. D1 produces the same proportions of inhibition of the H reflex when the H reflex is facilitated by plantarflexion or depressed by dorsiflexion.