"Adequate control theory" for human single-joint elbow flexion on two tasks

The control of distance and speed during single-joint human elbow flexion is accomplished by different models of activating the motoneuron pools. 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 sets of instructions: subjects moved either as fast and accurately as possible or in a specified time. The first task showed duration modulation, whereas the second, which required simultaneous control of distance and speed, showed both duration and intensity modulation. These results are interpreted in the context of a model for motor control, predicated on the existence of movement plans that use prior knowledge of the dynamics of the movement task to generate muscle activation patterns that produce joint torques. These plans use a simple algorithm based upon parameters of the task such as distance, load, and speed. From this plan, the kinematic trajectory emerges.