Abstract: A system and method for determining a patient force during a motion includes a tether adapted to be biased during a motion so that a tension force is applied. The tether is connected a motor and generates a tether force about the motor. The system controls the motor by generating a motor torque in a direction opposite the tether force. A recording module stores the motor torque at a plurality of intervals during the motion and a position of the tether. A display module generates a plot of a position of the patient versus a force generated by the patient. The position of the patient corresponds to the cumulative rotation of the shaft in the first direction about the axis of rotation of the shaft at each of the intervals. The force generated by the patient corresponds to the amount of motor torque at each of the intervals.