Figure 1

Subjects performed a goal-directed task by controlling a virtual prosthetic arm with their muscle activity. Biceps and triceps muscle activity was measured from subjects’ stationary dominant arms using electromyography (A). The task was to move the virtual arm counterclockwise through a waypoint and then clockwise back to a circle identifying the starting position (B). Subjects were instructed to move the virtual arm as quickly as possible and stop as close to the center of the starting circle as possible.