**2. Myoelectric prostheses**

The human body has been considered a perfect machine, in which all parts work in harmony one with each other. Most of us can control this "machine" without much effort, until some disturbance caused by disease or injury results in loss of some of its functionality.

The absence of limbs caused by trauma or congenital disorders, can affect our lives profoundly. Simple tasks such as walking or dressing can become extremely difficult or even impossible to execute. There is no doubt that the best solution for the loss of a limb might be the development of some kind of genetic manipulation that stimulates the regeneration of tissue. However, while this is not possible, the best we can do is to restore some of the lost functionality by means of artificial limbs.

For centuries, mankind seek ways to replace lost limbs by mechanical devices. Several ancient designs can be found in museums and libraries. However, the first artifact to be formally named artificial limb was a Roman prosthesis, made of wood and bronze, which appeared around 300 BC [9]. During the Middle Ages, while the poor wore "wooden legs", which were simple, inexpensive and stable, the rich nobles used devices made of iron, which were more decorative than functional. In 1818 Peter Ballif designed the first prosthesis actuated by movements of healthy parts of the body. Before this, the upper limb prostheses were heavy and depended on an able hand for operation [10]. Thereafter, a number of experiments have been carried out seeking the "perfect prosthesis", a device that could be similar to what Wolfe had visualized in 1952 in his book "*New York: Random House"* [11]:

*"They had perfected an artificial limb superior in many ways to the real thing, integrated into the nerves and muscles of the stump, powered by a built-in atomic energy plant, equipped with sensory as well as motor functions"* 

As we know, to date, this prediction has yet to be completely materialized, but much has been done since then. Due to the great number of casualties of World War II, the government of the United States created in 1945 a program of research and development from which scientists and engineers were deeply involved in projects aimed at the development of artificial limbs for amputees [10].

Another fact that lead to the acceleration of the researches in the area, was the large number of congenital defects caused by the use of a drug called Thalidomide. As describe by Soares [10], it was synthesized by the German laboratory Chemie Grünenthal in 1957 and marketed worldwide between 1958 and 1962. This drug was prescribed to minimize sickness during pregnancy. The Thalidomide consumers were not warned that the drug could exceed the placenta affecting the fetus. This oversight had a catastrophic effect: drug abuse, especially during the first trimester of pregnancy, has killed thousands of babies. Those who survived experienced birth defects such as deafness, blindness, disfigurement, and especially the shortening or absence of members. Responding to this tragedy, several research centers intensified the efforts towards the design of artificial limbs as an attempt to improve the lives of those children.

Also, during that period, russian scientists had introduced a prosthetic hand controlled by a signal generated by the activity of remaining muscles from amputated limbs [8]. That type of control has been described as "myoelectric control" and the prosthesis, by extension, has been described as "myoelectric prosthesis".
