Practice effects on the timing and magnitude of antagonist activity during ballistic elbow flexion to a target.

This study examined changes in antagonist timing and magnitude in response to ballistic elbow flexion practice. Seventeen men performed 400 ballistic elbow flexion trials to a target in the horizontal plane over 4 days of testing. A potentiometer and microswitch system at the elbow axis of rotation of a manipulandum recorded angular displacement and movement onset. Surface electrodes (Beckman Ag/AgCl) monitored the triceps brachii lateral head, and the electromyographic (EMG) signals were bandpassed between 20 and 300 Hz. The antagonist EMG burst was divided in two: early low-level activity (ANT1), and the large portion of the burst which occurs near target achievement (ANT2). Movement time decreased from 178 ms on the first test day to 136 ms on the last session. As practice improved the speed of limb movement, onset of the first component (ANT1) remained unchanged, while the second component (ANT2) started earlier. The magnitude of both portions of the antagonist burst increased from the first to last test day, but the change in ANT2 relative to ANT1 was more pronounced. These findings are used to explain discrepant observations in the literature for the temporal measure.