NOVELTY - The trainer has a planar spiral spring for forming a hook at an external end such that the hook is fixed to a latch plate on an external side of a positioning base. The spring is forced and tightened to apply torque in a reverse direction to a main shaft and transmit the torque to a winch (33) for providing a constant pulling force to a steel wire (23) when the winch is driven and rotated by the steel wire. A roller bearing in a belt pulley is separated from the pulley without driving a motor armature when the shaft is rewound, and the winch rewinds the steel wire during a power disconnection.    USE - Powered strength trainer for building muscles, promoting physiological functions, and maintaining good health, for use by heart disease patients or physical therapy patients, elderly and women.    ADVANTAGE - The trainer has simple and light structure, thus reducing weight and volume of the machine. The motor is utilized for producing pulling force, resistance and vibration force, and several vibration waveforms that are provided for the user's choice, thus adjusting frequency and amplitude as required by the user. The front end of the main shaft provided with a roller pulley and a belt pulley prevents driving of a heavy motor armature while the main shaft is rewound, so that the winch rewinds the steel wire quickly without falling out during a power failure. The trainer detects a user's heartbeat rate, and automatically reduces load when the user's heartbeat exceeds a safe range. The optical interrupt disk is installed on a winch main shaft, and a pair of optical couplers is installed on periphery of the optical interrupt disk and a movement path sensor, so that a pulse signal generated by the optical coupler is transmitted to a positive and negative rotation signal decoder in the controller when the winch drives the optical interrupt disk to transmit positive and negative rotation signals to the microcomputer control panel, thus controlling a curved load, and compensating a load current to provide a smooth and real-world setting to users. The motor can be utilized for producing a continuous, smooth and variable resistance, thus providing a comfortable use for the user, and minimizing exercise injuries.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic circuit diagram of a powered strength trainer.    Steel wire (23)    Winch (33)    Signal processing device (43)    Microcomputer control panel (50)    Heartbeat detection electrode (60)