Sequence of preparatory set for response movement.

Electromyographic reaction times (EMG-RTs) of the right biceps brachii muscle were examined for two movement patterns, elbow flexion and forearm supination, in 8 healthy male subjects under simple and complex RT conditions with varied preparatory intervals (PIs): 0, 200, 400, 600, and 800 msec. In the simple RT condition, the subject was informed of the movement patterns to be performed prior to beginning the trials. In the complex RT condition the subject had to choose one of the two movement patterns at the time of the presentation of a warning signal. The results indicated that: (1) compared with the simple RT condition a delay of about 100 msec. in over-all mean EMG-RT was observed at PI = 0 msec. in the complex RT condition; (2) the difference of over-all mean EMG-RT between the two RT conditions disappeared when PI = 400 msec.; and (3) the difference in EMG-RTs between flexion and supination in the complex RT condition became the same as that in the simple RT condition when PI = 700 msec. It is assumed that the preparatory set for response movements is organized in an order, resulting in the differentiation of RT.