Multijoint movement control in Parkinson's disease

Impairments in the performance of complex actions in Parkinson's disease (P D) patients are well documented. The aim of the present study was to invest igate potential mechanisms that may be contributing to impaired movement pe rformance in PD patients. PD patients and age-matched control subjects perf ormed rapid pointing movements to a series of four tabletop targets. The he ight of the table was adjusted until the targets could be achieved with arm movements in the horizontal plane. The targets were arranged such that tar get 1 required elbow extension only and targets 2-4 required increasing amo unts of horizontal shoulder flexion in addition to the elbow extension. Whi le the control subjects accelerated and decelerated the elbow and shoulder joints simultaneously regardless of the target location, the PD patients de composed motion during the acceleration phase by accelerating first the sho ulder and then the elbow joint. For PD patients this decomposition of arm s egments was associated with greater coactivation of the muscles about the e lbow when elbow extension and shoulder flexion were simultaneously required (targets 2-4), in contrast to the single joint action. The control subject s decreased elbow joint coactivation while the patients increased it across the four targets. The resulting peak interaction torques at both the elbow and shoulder joints occurred relatively later for the PD patients. The coa ctivation patterns observed in PD patients may reduce the ability to take a dvantage of interaction torques and may also contribute to joint motion dec omposition.