Controlling velocity in rapid movements.

It has often been reported that subjects prefer to use a strategy in which they vary movement velocity and peak amplitude in a linear fashion. In this study, control of velocity and amplitude in rapid reciprocating movements of the interphalangeal joint of the thumb was investigated by examining movement trajectories and patterns of activity in the extensor pollicis longus (EPL) and flexor pollicis longus (FPL) muscles. In controlling either amplitude or peak flexion velocity without constraint, subjects always used a strategy in which peak extension velocity and peak flexion velocity had strong linear correlations with movement amplitude. When they were required to keep either amplitude or peak flexion velocity fixed their movements were still biased toward a strategy in which peak velocity and movement amplitude covaried. It is suggested that the preferred strategy is related to a basic principle of scaling the magnitude and duration of a velocity profile in order to achieve different movement amplitudes.