Strategy and learning effects on perturbed movements: an electromyographic and kinematic study.

The effects of practice and movement strategy were studied in a goal-directed movement with different levels of perturbation applied in four independent groups (0%, 20%, 50% or 100%). The phase-plane trajectory data revealed that for all subjects there was a decrease in the mean trajectory variability with learning and that variability was affected by the level of uncertainty confronting the subjects. Both the average electromyographic (EMG) profiles and the mean subject variability for agonist and antagonist muscles decreased with learning. In each experimental group a specific interaction developed between reflex responses and voluntary activity to create a balanced level of EMG activity to improve the performance with learning.