The reaction time of muscular relaxation was investigated in the elbow flexors. The time interval from the onset of a light stimulus to the response of the elbow flexors was measured using EMG. The subjects were 20 healthy male adults. There was no difference in the reaction time between muscular relaxation and muscular contraction. In terms of mean values for twenty subjects, there was no significant difference in the electrical response of M.biceps brachii between muscular contraction and relaxation. Significant individual differences were noted.