Abstract: An exercise apparatus permitting external torque applied in resistance to an exercise to be adjustably controlled during the course of the exercise to match the external torque applied with the internal torque produced by the muscles involved in the exercise. The exercise apparatus is disclosed embodied in a sit-up apparatus in which weights can be adjustably mounted on weight arms extending in line with the subject's torso and behind the subject's torso for normal subjects, and below the torso to assist weak subjects for rehabilitative purposes.