A myoelectric prosthesis is one which is controlled by the electrical activity of a muscle, i e. by a myoelectric signal. They are powered by electricity from a battery, in which case the Myoelectric signal controls the flow of energy from the battery to an electric motor. Myoelectric control of prosthesis or other system utilizes the electrical action potential of the residual limb’s muscles that are emitted during muscular contractions. These emissions are measurable on the skin surface at a microvolt level. The emissions are picked up by electrodes and are amplified for use as control signals to the functional elements of the prosthesis. The myoelectric emissions are used only for control. Because the electrical signals are not powerful enough to operate the electric motors in the prosthesis, a rechargeable 6-volt battery, which is accommodated in a socket in the prosthesis, is used to operate the motors which, in turn, produce the movements of the prosthesis. Despite the efforts of the media and others to convince us that a MYOELECTRIC prosthesis is something new from the space age, it is worth mentioning that the first PROSTHESIS, myoeIectric prosthesis was created in the period 1944-1948 by Reinhold Reiter, then a physics student at Munich University and so on.
Three Categories of Upper-limb Prosthetics used in myoelectric prostheses are three major categories
of upper-limb prosthetics: (1) cosmetic, (2) body powered and (3) myoelectrically controlled self-powered prostheses. The primary purpose of an arm prosthetic is to mimic the appearance and replace the function of a missing limb. While a single prosthetic that achieves both a natural appearance and extreme functionality would be ideal, most artificial limbs that exist today sacrifice some degree of one for the other. As such, there is a wide spectrum of specialized prosthetics that range from the purely cosmetic (which are inert) to the primarily functional (whose appearance is obviously mechanical). Myoelectric prosthetics are an attempt to serve both purposes of an artificial limb equally, without sacrificing appearance for functionality.
Myoelectric prosthetics have a number of advantages over body-powered prosthetics. Since it uses a battery and electronic motors to function, the myoelectric artificial limb does not require any unwieldy straps or harnesses to function. Instead, it is custom made to fit and attach to the remaining limb (whether above the elbow or below) with maximum suspension using suction technology. Once it is attached, the prosthetic uses electronic sensors to detect minute muscle, nerve, and EMG activity. It then translates this muscle activity (as triggered by the user) into information that its electric motors use to control the artificial limbs movements. The end result is that the artificial limb moves much like a natural limb, according the mental stimulus of the user. The user can even control the strength and speed of the limb’s movements and grip by varying his or her muscle intensity. As well, the acute sensors and motorized controls enable greater dexterity, even allowing the manipulation and use of small items like keys or credit cards through functioning fingers. In addition to this extreme functionality, the myo-electric artificial limb needs not sacrifice any of its cosmetic appearance. The most advanced versions of these prosthetics are incredibly natural and on par with purely cosmetic limbs.
The weight and the cost are currently the primary disadvantages of these. Their heavy weight is due to the fact that the myoelectric artificial limb contains a battery and motor inside, and unlike the bodypowered prosthetic, it does not use any harnesses to counter-balance the weight across the body. This is an admitted trade-off for a more natural appearance. As well, as the technology develops, the weight of each component will eventually become lighter and less of a problem. The other disadvantage of myoelectrics is the cost. While it is currently more expensive than other kinds of prosthetics, it also offers the best quality in regard to both cosmetics and functionality. Like the problem of weight, it is estimated that the cost will eventually diminish as the technology becomes cheaper to reproduce.