Parkinsonian bradykinesia is due to depression in the rate of rise of muscle activity.

Parkinsonian bradykinesia is defined by a slowness in the execution of movement. We studied the pathophysiology of this symptom in rapid arm-reaching movements to a visual target carried out in a reaction-time task. The major cause of bradykinesia was found to be depression in the rate of rise of electromyographic activity. The amplitude of the peak of this activity did not change significantly. There was no change either in the sequential activation of muscles, in the amount of co-contraction activity, in the accuracy of aim toward the visual target, or in the movement trajectory.