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People generally select a similar speed for a given motor task, such as reaching for a cup. One well established determinant of movement time is the speed–accuracy trade-off: movement time increases with the accuracy requirement. A second possible determinant is the energetic cost of making a movement. Parkinson's disease (PD), a condition characterized by generalized movement slowing (bradykinesia), provides the opportunity to directly explore this second possibility. We compared reaching movements of patients with PD with those of control subjects in a speed–accuracy trade-off task comprising conditions of increasing difficulty. Subjects completed as many trials as necessary to make 20 movements within a required speed range (trials to criterion, N_c). Difficulty was reflected in endpoint accuracy and N_c. Patients were as accurate as control subjects in all conditions (i.e., PD did not affect the speed …