Reinforcement of reciprocal inhibition by contralateral movements in man.

A reduction of flexor carpi radialis H reflex size was produced by submotor threshold stimulation of the radial nerve. This reduction reflects reciprocal inhibition exerted by the inhibitory IA interneuron. The effects of contralateral movements on IA reciprocal inhibition were studied in eight normal subjects. Active contralateral arm movement appeared to significantly increase the degree of reciprocal inhibition without affecting the unconditioned reflex. A minor enhancement of reciprocal inhibition was also noted after passive mobilization. Results are discussed in terms of contralateral segmental afferent fibers influencing IA interneuronal excitability. They strongly suggest that contralateral muscular IA afferents may reinforce reciprocal inhibition in man.