PRINCIPLES FOR LEARNING SINGLE-JOINT MOVEMENTS .1. ENHANCED PERFORMANCE BY PRACTICE

This study investigated changes in myoelectric and mechanical variable s for movements made ''as fast as possible'' as a function of practice in the context of the dual-strategy hypothesis of motor control (Gott lieb et al. 1989b). Five male subjects made 1400 rapid elbow flexion m ovements in ten blocks of 20 trials over seven experimental sessions. Improved performance was defined as increased peak movement velocity, decreased peak velocity variability, increased acceleration and decele ration, a proportionately greater increase in peak deceleration than p eak acceleration, and greater consistency in terminal location. The ch anges observed over experimental sessions were very similar to (but la rger and more consistent than) those seen for the first experimental s ession, with the partial exception of the timing of the antagonist ele ctromyogram (EMG). In general, the increases in the values of the meas ured mechanical variables covary with myoelectric measures in the same way as when subjects are asked to intentionally change speed in accor dance with the rules of the speed-sensitive strategy (Corcos et al. 19 89). However, there are differences between subjects in the extent to which speed changes can be attributable to the agonist muscle, the ant agonist muscle, or in the timing between the muscles. In one of the fi ve subjects, the latency of the antagonist EMG decreased over blocks o n the 1st day but increased over experimental sessions and was consequ ently activated proportionately later in the movement. This suggests t hat extended practice can give at least some subjects flexibility in m odifying the motor programs that underlie movement.