Reaction time in simultaneous motions.

EMG-RTs of biceps and triceps brachii muscles were measured in 3 different tasks: isolated motions, flexion or extension of either forearm; bilateral symmetrical motions, flexion or extension of both forearms; bilateral opposite motions, flexion of a forearm and extension of the other. EMG-RTs of opposite motions were slower than those of isolated and symmetrical motions, EMG-RTs of symmetrical motions were nearly equivalent to those of isolated motions. Simplicity and complexity of simultaneous motions are discussed.