Analysis of stereotyped voluntary movements at the elbow in patients with Parkinson's disease

Patients with Parkinson's disease performed several different stereotyped elbow flexion tasks, and the electromyographic (EMG) patterns from biceps and triceps were compared with previously established normal standards. The EMG pattern during a smooth flexion task was almost always abnormal and was characterized by alternating activity in biceps and triceps. The EMG patterns during a fast flexion task were also usually abnormal although they were always composed of bursts of EMG activity of normal duration appearing alternately in the agonist and antagonist muscles. These bursts, associated with movements of the limb, have a superficially similar appearance to the EMG bursts seen with tremor-at-rest, but certain physiological differences are demonstrated. This study demonstrates that both slow (ramp) and fast (ballistic) movements are clearly abnormal in these patients with disease of the basal ganglia. In a task designed to investigate antagonist inhibition before agonist activity, a majority of the patients performed normally. This suggests that, contrary to previous claims, slowness of movement (akinesia/bradykinesia) is not due either to failure to relax or to rigidity of antagonist muscle.