Semi active devices to modify the stiffness or the damping of systems received significant attention in the recent years. In this paper, two solutions of a variable compliance device to change the physiotherapists feeling of the thorax compliance of a 6-month old infant torso training simulator are presented. A first solution, using a variable orifice device which allows to change the compliance by changing the radius of a flow pipe is proposed. Another solution is to use a magnetorheological fluid damper. Both systems are presented in detail and discussed especially for their applicability to be integrated in the simulator.