FIG. 2.

Experimental setup for measuring isometric forces exerted by the index finger. The subject is configured with the shoulder abducted about 15° and the elbow flexed to 90° and positioned in full pronation. The wrist is immobilized with rigid casting tape and secured within a fixture. The right index finger is similarly immobilized and secured just distally to the distal interphalangeal joint, connected to a 6 degree-of-freedom load cell through a rigid tube. Visual feedback of abduction–adduction (left–right direction) and flexion–extension (down–up) forces is displayed to the subject on a computer screen, with instantaneous force and the target direction and magnitude displayed in polar coordinates. The subject exerts forces to move the cursor (indicated by a dot) toward the target force (intersection of ray with circle). The example shows the force trace recorded over a trial.