A semi-actuated above knee prosthetic system (100), includes a shank link(105) coupled to an artificial foot (108),a knee mechanism (107) connected to the shank link (105) and a thigh link(103) attached to an above-knee remaining lower limb(110) of an amputee, is operable in two modes controlled by a signal processor(130) linked to various sensors(120,122,124,126,127). In the actuated mode, power is delivered to a torquegenerator (104) connected to the knee mechanism(107) to move thigh (103) and shank links (105). In the un-actuated mode, acontrol circuit (204) operates in a non-powered man-nerwith modulated resistance in the knee mechanism (107). Power is deliveredthrough an electric motor (202) connected to abattery source (205) and employed to drive a hydraulic pump (201) as part ofan overall hydraulic power unit (200) including thetorque generator (104)
