Premotor and motor reaction time as a function of force output

The effects of variation in force output on fractionated reaction times (RTs) in elbow extension for 5 normal adults were examined. Force was manipulated by instructing the subject to respond with much or little force, and force output was measured by an accelerometer. Premotor RT increased with increased force output, indicating that organization of force for movement could affect not only the movement speed but the timing of its initiation. Motor RT became longer at manipulated force production than the control response, suggesting that motor RT was also influenced by the central processing of movement organization. The early electromyographic activities of the triceps brachii muscle were examined and discussed in relation to the production of force for initiation of movement.