Whereas passive prostheses are fitted onto the patient after the amputation of an arm, hand or finger and are mostly cosmetic in function, active prostheses have much more potential. They can transform the movements of other body regions to movement in the artificial limb. Belts or harnesses, for example, effect the direct transfer of the power from the muscle to the prosthesis. The range of movement possible depends upon the level of the amputation, the length of the residual limb, the age of the patient, his body build and fitness. Myoelectrically controlled prostheses possess their own drive and power source. They control movement through the electrical action potentials of the residual limb muscles, which are detected, amplified and transmitted with help of electrodes.