NOVELTY - The device has a base body (30) located on a base frame (20). A movement path sensor (54) comprises an optical interrupt disk installed on and linked to an axle (41). An optical coupler (53) is installed at a periphery of the disk, such that positive and negative rotation signals are transmitted to a microcomputer control panel for controlling a curved load and compensating a load current appropriately when the axle drives the disk to transmit a pulse signal generated by the coupler to the positive and negative rotation signal decoders in the current controller.    USE - Loading device for a leg extension machine.    ADVANTAGE - The device allows the user to press a key on the microcomputer control panel to switch the rotating direction of the motor, to change an internal or external exercise, thus improving the convenience, safety and function of using the extension machine. The torque of the main shaft of the motor is used to replace traditional weight stacks to achieve a light and simple structure, such that the weight, volume, and noise of the machine can be reduced effectively. The device controls the exercise load, so that the leg extension machine can achieve the computerized adjustment and comfortable usage effects. The loading device monitors an exerciser's heartbeat rate and the load is reduced automatically to drop the heartbeat rate gradually to the safe range and assure the exerciser's health if the exerciser's heartbeat rate exceeds a safe range. The device has a simple and light structure, reduces the weight and the volume of the machine greatly, and provides a noise-free operation and a computerized adjustment and produces continuous and smooth variable resistance, so as to achieve a comfortable usage and greatly reduce the risk of exercise injuries.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective front oblique view of a loading device.    Base frame (20)    Base body (30)    Axle (41)    Optical coupler (53)    Movement path sensor (54)