Kinematic and myoelectric analysis of skill acquisition: I. 90cm subject group

The purpose of this study is to define modifications in myoelectric activity and parameters of movement occurring during the acquisition of a novel motor skill. Twenty-three subjects practiced a shoulder flexion task, the goal of which was accuracy, for 103 trials at 1 sitting. The subject-to-target distance was 90cm. Synchronized cinematography and electromyography (EMG) were used to gather data intermittently throughout the learning sequence. The criterion measure, the performance score, was significantly altered during the learning sequence, with the majority of learning occurring very early in the practice period. To effect this alteration, results indicated that success required specific modifications in the kinematics of throwing behavior to include the following: 1) A 10% decrease in limb angle at ball release; 2) a decrease of 30% in the movement time for the limb excursion; and 3) a 60% increase in velocity of the limb at ball release. Alterations which occurred simultaneously in myoelectric variables included the following: 1) An early (within 3 trials) and sizable overall increase in total electrical activity for agonists and antagonists alike; 2) an increase in premovement activity for each of the muscles; 3) changes in coordination or the sequential firing of the various muscles; 4) alterations in the times needed to reach peak electrical activity; and 5) replacement of variables representing total electrical output by myotemporal variables, indicating that the subjects became dependent upon minor adjustments in temporal sequencing later in the practice session for any further performance refinements or improvements.