PRACTICE EFFECTS ON THE TIMING AND MAGNITUDE OF ANTAGONIST ACTIVITY DURING BALLISTIC ELBOW FLEXION TO A TARGET

This study examine changes in antagonist timing and magnitude in respo nse to ballistic elbow flexion practice. Seventeen men performed 400 b allistic elbow flexion trials to a target in the horizontal plane over 4 days of testing. A potentiometer and microswitch system at the elbo w axis of rotation of a manipulandum recorded angular displacement and movement onset. Surface electrodes (Beckman Ag/AgCl) monitored the tr iceps brachii lateral head, and the electromyographic (EMG) signals we re bandpassed between 20 and 300 Hz. The antagonist EMG burst was divi ded in two: early low-level activity (ANT1), and the large portion of the burst which occurs near target achievement (ANT2). Movement time d ecreased from 178 ms on the first test day to 136 ms on the last sessi on. As practice improved the speed of limb movement, onset of the firs t component (ANT1) remained unchanged, while the second component (ANT 2) started earlier. The magnitude of both portions of the antagonist b urst increased from the first to last test day, but the change in ANT2 relative to ANT1 was more pronounced. These findings are used to expl ain discrepant observations in the literature for the temporal measure .