FIGURE 1.

Experimental set-up. Subjects were seated in an experimental chair with the right leg extended. The apex of the patella was aligned with the center of rotation of the servomotor. The right leg was fixed within a coupling ring with a cast placed around the ankle joint. The coupling ring was fixed to a servomotor actuator with a precision potentiometer and tachometer. The knee was fitted within a bracket mounted firmly at the medial and lateral femoral epicondyles. Together with a thigh strap, the brackets isolated the knee varus–valgus movement from the frontal plane movement of the hip joint.