Modifications of neuromuscular activity and improvement in performance of a novel motor skill.

The relationship between the modifications in the myoclectrical activity after practice and the performance enhancement was examined regarding a ballistic movement of the elbow. 41 subjects practiced a novel throwing skill, which involved the throw of a ball, performing elbows flexion. Surface electromyograms of four muscles in the elbow region were analyzed, aiming at identifying the changes in the timing and the intensity of muscle activation that may account for improved performance. A repeated-measures analysis of variance identified an improvement in performance scores after practice and a significant decrease in the EMG for the agonists and the primary antagonist. Moreover, a significant increase in the delay of the activity onset in the antagonists was observed after practice. The variations of the EMG for the biceps brachii and the anconeus were significantly elated to improvement in performance. It was concluded that the modifications in the electrical activity of those to muscles were primarily responsible for the physical alterations associated with improved performance.

Contextual interference effects in learning novel motor skills.

The present study investigated the generalizability of contextual interference effects by extending previous laboratory and field research to novel movements controlled by different motor programs. 30 men and 33 women learned novel throwing and kicking tasks, practicing with blocked, serial, or random schedules. The subjects practiced the tasks four days a week for two weeks and then were given a postest. One week later subjects were given a retention test. Significant improvements in performance were found for all groups for both tasks; however, a significant effect for practice condition was found only for the throwing task during retention, for which the random practice schedule led to better learning than the blocked and the serial practice. These findings suggest that the blocked, serial, and random practice methods could be effectively used for tasks controlled by different motor programs but must be practiced in the same teaching session, without expecting one to be more effective in learning than any other.

Coping with systematic bias during bilateral movement.

The present studies examined the nature of kinematic interlimb interference during bilateral elbow movements of 1:1, 2:1 and 3:1 frequency ratios and the manner in which subjects cope with coordination bias. Analysis of movement trajectories in the first experiment indicated progressively greater angular velocity assimilation across 2:1 and 3:1 conditions. The desired temporal relationship was maintained by slowing or pausing the low-frequency movement at peak extension while the high-frequency arm produced intervening cycles. An increase in amplitude was also evident for concurrent, homologous cycles. Movement smoothness was emphasized and additional practice was provided in a second experiment. This resulted in dissociated peak angular velocity between limbs and eliminated hesitations and amplitude effects. Bias was still evident, however, as an intermittent approach toward a 1:1 ratio within each cycle. This systematic tendency was somewhat greater at the lower of two absolute frequency combinations but was not influenced by the role of each arm in producing the higher or lower frequency movement. The findings from the first experiment suggest that subjects initially accommodate interlimb kinematic assimilation, while producing the intended timing ratio, by intermittently slowing or pausing the lower-frequency movement. This attenuates the need for bilaterally-disparate movement parameters and provides additional time for organizing residual kinematic differences, perhaps reducing "transient coupling." Evidence from the second experiment indicates that subtle relative motion preferences are still evident following sufficient practice to perform the movements smoothly. The within-cycle locations of the points of greatest interlimb bias for the 2:1 rhythms were positively displaced from those previously observed for 1:1 oscillations. The persistent coordination tendencies noted in both experiments perhaps reflect an assimilation/compensation cycle and constitute one potential source of the systematic error that often emerges during the acquisition of complex skills.