The effects of movement velocity, mass displaced, and task certainty on associated postural adjustments made by normal and hemiplegic individuals.

The activation times for trunk and leg muscles were examined in normal and left hemiplegic subjects who raised their right arms at different velocities in self-paced or reaction time conditions. Activity in these postural muscles preceded arm displacement, and they were activated in a similar sequence during all types of rapid movements. The presence and sequencing of associated postural adjustments were more variable during slow movements.