Electromyographical Study of Reflex, Premotor, and Simple Reaction Time of Relaxed Muscle to Joint Displacement

Abstract

Ss (N=30) responded to a sudden arm drop from an electromagnet by abducting the failing arm and by abducting the nonstimulus arm from a RT switch. EGMs from 30 randomized trials were monitored from the middle portions of the relaxed deltoideus muscles. Ipsilateral reflex latencies averaged 24 msec. and were characterized by rapid EMG bursts followed by a silent period. The more sustained EMG bursts had shorter latencies in the contralateral limb (72 msec.) than in the ipsilateral limb (88 msec.). Contralateral RT averaged 180 msec. The presence of a stretch reflex in the form of a synchronous volley appeared to delay ipsilateral premotor times.