Abstract: A processor controlled eccentrically loaded exercise machine for providing a resisting or powering force which can be varied by position in order to carry out positive or negative exercise strokes. A variable torque motor provides a torque to a torque coupler. The torque coupler is coupled to the user interface device through a mechanical link. During a positive exercise stroke, the motor supplies a torque to a slipping torque coupler so as to provide an eccentrically loaded resisting force, which resists the force exerted by the user in moving the exercising device as his muscle contracts. During a negative exercise stroke, the torque coupler engages to provide a powering force, as supplied by torque motor, against the contracted muscle of the user. A position sensor and a load cell are coupled to the user interface device for providing position and force signals to the processor.