Coordination of grip and load forces during vertical point-to-point movements with a grasped object in Parkinson's disease.

Thirteen patients with Parkinson's disease and 13 age-matched control subjects performed vertical point-to-point arm movements with an instrumented object, starting and ending with the object being held stationary. All Parkinsonian patients were tested on medication. Parkinsonian patients retained all aspects of predictive grip force control. Compared with healthy controls, they generated similar static grip forces during stationary holding and similar force ratios between maximum grip and load force, reflecting effective grip force adjustments in relation to movement-induced inertial loads. Grip and load force maximums coincided very closely, indicating that temporal aspects of predictive grip force regulation were also unaffected. However, Parkinsonian subjects showed additional oscillations in acceleration and grip force due to tremor and produced significantly slower arm accelerations due to bradykinesia. The results suggest that Parkinson's disease does not significantly impair the anticipation of movement-induced load fluctuations during voluntary arm movements with a grasped object performed on medication.