Abstract: The invention relates to a motor-driven device for concentric, isometric and eccentric muscle development, the triggering direction of which is reactive to the direction of the force of the user. The invention specifically relates to a motor-driven device with two operating directions, with reacts to the force of a user in order to counteract with an adjustable muscle development load in a reversible movement. It consists of a reversible motor-driven support which moves a mobile support (2)(30)(51) on which a part of the body is supported, and provides a muscle development load; and a stationary support (3)(33)(52) on which another part of the body is supported so as to counteract the motor-driven force of the mobile support (2)(30)(51).