Abstract: A movable limb rehabilitation device such as an orthosis or prosthesis part is connected to a drive by a transmission which converts rotary into linear reciprocatory motion. The transmission includes a cylinder coupled to the drive for rotation therewith and having two separate threads of opposite pitch, a sleeve and a spindle respectively threadedly mounted on the threads for linear movement in relation to the cylinder and non-rotatably held on the cylinder whereby rotation of the cylinder by the drive causes the linear movement of the sleeve and spindle, and a tackle with a cable or chain having two ends facing the drive, the ends being respectively affixed to the sleeve and spindle and the tackle being connected to the movable orthosis or prosthesis part for moving the same in response to the rotary motion of the drive.