Kinematic properties of slow arm movements in Parkinson's disease.

Present pathophysiological concepts of bradykinesia stress an impairment of fast movements in Parkinson's disease. It is, however, unknown whether "bradykinetic" movements are different from slow movements of normal subjects. We recorded trajectories of unrestrained "natural" arm movements from normal subjects and patients with Parkinson's disease. The experiment required the execution of pointing movements for different movement distances and velocities. The shape of trajectories was found to be changed in Parkinson's disease. The steepness of the initial segment and the relation between steepness of the initial segment and final segment both exceeded corresponding values in normal subjects. An analysis of velocity profiles showed an impaired synchrony of vertical and horizontal velocity components. The difference from normal subjects increased with movement velocity. Parkinsonian patients suffered from a fundamental defect in the composition of complex sequences of motor programs required to perform natural arm movements.