Muscles Alive: Their Functions Revealed by Electromyography 3rd ed

Abstract

Electromyography is the study of muscle function through the inquiry of the electrical signal the muscles emanate. Inherent movement is the prime sign of animal life. For this and many other reasons, man has shown a perpetual curiosity about the organs of locomotion in his own body and in those of other creatures. Indeed, some of the earliest scientific experiments known to us concerned muscle and its functions. With the reawakening of science during the Renaissance, interest in muscles was inevitable. Leonardo da Vinci, for example, devoted much of his thought to the analysis of muscles and their functions. So, too, did the acknowledged “father” of modern anatomy, Andreas Vesalius, whose influence through his monumental work, the Fabrica, extends down to this day. In one sense, however, the heritage of Vesalius was unfortunate because it stressed the appearance and the geography of dead muscles rather than their dynamics (Fig. 1.1). During subsequent years, a series of scientists gave life back to the muscles. The first logical deduction of muscle-generated electricity was documented by Italian Francesco Redi in 1666. He suspected that the shock of the electric ray fish was muscular in origin and wrote, “It appeared to me as if the painful action of the electric ray was located in these two sickle-shaped bodies, or muscles, more than any other part” (Biederman, 1898). The relationship between electricity and muscle contraction was first observed by Luiggi Galvani in 1791. In his epochmaking experiments, he depolarized the muscles of a frog’s legs by touching them with metal rods (see Fig. 1.2). His concept of “animal electricity” was enthusiastically received throughout Europe. Galvani’s original book, De Viribus Electricitatìs, has been translated into English by Green (1953). This discovery is generally acknowledged as representing the birth of neurophysiology, thereby making Galvani the father of this field which continues to expand rapidly. Many rushed to confirm Galvani’s results and praise his discovery. Among them was Alessandro Volta, who initially embraced the discovery and in retrospect wrote “it contains one of the most beautiful and surprising discoveries and the germ of many others” (Volta, 1816). But, within two years, in 1793, Volta questioned Galvani’s findings by proving that dissimilar metals in contact with an electrolyte (such as those present in body tissues) would generate an electric current. In the following year Galvani reaffirmed his concept when he found that a muscle contraction could be elicited by placing the free end of a nerve across a muscle without the intervention of metals.