A mechanical and electronic apparatus which utilizes off-setting positive and negative muscle effort to provide a complete body muscle exerciser. The exerciser is constructed so that left side and right side symmetrical muscle groups are caused to work against one another, with one muscle group moving in extension providing resistance for the symmetrical muscle group to work thereagainst in contraction. A mechanical gear drive train is interposed between the opposing symmetrical muscle groups to transmit the forces exerted thereby, and to guide the user's limbs so that the directions of motion are exactly opposite, and to assure that one muscle group contracts simultaneously with the extension of the other. Electrical sensors are coupled to the mechanical drive train to indicate the resistance being experienced by each muscle group; and also to indicate the position of the muscle groups, that is, the distance they have moved in their excursion. The electrical signals produced by the sensors are processed in a microcomputer which drives appropriate audio and visual displays.