Human ballistic arm abduction movements: effects of L-dopa treatment in Parkinson's disease.

In patients with Parkinson's disease who had never previously been treated with any antiparkinsonism drug, we studied the effects of L-dopa on ballistic arm abduction movement in a step-tracking task. L-Dopa treatment increased the mean velocity of the initial movement towards the target without loss of accuracy and with improved motor performance under open-loop conditions. Performance also improved in motor tasks with expected perturbation. EMG patterns of arm abduction movements showed abnormal features in untreated patients and improved after L-dopa treatment.