ADEQUATE CONTROL-THEORY FOR HUMAN SINGLE-JOINT ELBOW FLEXION ON 2 TASKS

The control of distance and speed during single-joint human elbow flex ion is accomplished by different modes of activating the motoneuron po ols. Distance is controlled by modulating the duration of activation, while speed is controlled by modulating the intensity. The experiments reported on here compare movements of different distances under two s ets of instructions: subjects moved either as fast and accurately as p ossible or in a specified time. The first task showed duration modulat ion, whereas the second, which required simultaneous control of distan ce and speed, showed both duration and intensity modulation. These res ults are interpreted in the context of a model for motor control, pred icated on the existence of movement plans that use prior knowledge of the dynamics of the movement task to generate muscle activation patter ns that produce joint torques. These plans use a simple algorithm base d upon parameters of the task such as distance, load, and speed. From this plan, the kinematic trajectory emerges.