An automatically controlled exercise machine which is intended to produce optimal development of skeletal muscle strength for athletic purposes and in physical rehabilitation. The mechanical configuration of this machine is based on a linkage comprised of a series of links connected together so as to allow movement of each link relative to another. Each link is provided with a separate powering device which drives it relative to another link. This linkage interacts with the user by means of various removable attachments located on the outermost link. These independent powering devices are controlled by a feedback control system, so that the user interaction point moves along any specified path in response to forces exerted by the user, and simultaneously provides resisting forces which vary in any desired manner according to position, speed, time, and user-exerted forces.