Kinematic and electromyographic changes that occur as a function of learning a time-constrained aiming task

The present study attempted to examine the changes associated with learning two time-constrained aiming movements at the neuromuscular and behavioral levels of analysis. Electromyographic data and movement kinematics were used to assess changes due to practice. Eight right-handed females were required to perform a 45 degrees horizontal forearm extension in either 200 ms or 500 ms for 100 trials on each of four consecutive days. Both groups demonstrated an improvement in performance and a decrease in within-subject variability in the endpoint response measures, movement trajectory, and myoelectric pattern. With practice, there was a decrease in the amount of cocontraction between the agonist and antagonist muscles during movement execution, which indicated an elimination of unwanted neural activity. For the 200 ms task, the acceleration profile became symmetrical and triphasic myoelectric pattern became evident. The deceleratory phase of the 500 ms task was longer than the acceleratory phase, and a biphasic pattern became apparent. The results suggest that two different control strategies were developed in the execution of the two movements examined. In addition, the relative invariance of the spatial-temporal dependent measures, as compared to the variability of the EMG, led us tot he conclusion that the movement planning hierarchy was concerned with the spatial-temporal domain, whereas the amplitude and timing of muscular activity were planned at a lower level and thus played a subordinate role in movement production.