However, where the physical limitations of the amputee are such that a conventional control system is less practical, as in a high level bilateral amputation, the option to move to an externally powered device becomes an excellent alternative. Switches come in a variety of designs such as harness switches, push button switches which can be mounted inside or externally on the socket, and membrane push switches which are internally mounted. A switch requires some gross body motion to operate, for example, the push button is depressed by a chin, opposite limb, residual limb, or digit. A pull switch is cable operated and requires a few degrees of excursion, less than with a conventional prosthesis. Many amputees regard the use of high technology devices and the convenience that they offer as desirable and beneficial in the appropriate setting.
Myoelectric controls reduce gross body motions and limit harnessing.
The trade-offs are speed and weight. A conventional prosthesis is faster than a motor driven device, and the electric prosthesis may weigh more than the conventional because of the addition of the power supply and the powered devices themselves. For the below elbow amputee, a self-suspended myoelectric prosthesis entirely eliminates the need for a harness. It utilizes the natural muscle flexion in the residual limb to produce the signal to open and close the electric terminal device. The above elbow amputee fitted for an electric prosthesis may use myoelectric control or switch control for the electric devices, or a combination of the two.