Vodovnik (1968) has suggested that medical engineering may generally be divided into the three areas of diagnostics, therapeutics, and replacement of lost function. Myo-electric (muscle-electric) signals find usage in each of these areas. In this paper the emphasis is on a method for processing myo-electric signals to be used in devices which are designed to replace lost function, particularly as applied to loss of function in the extremeties resulting from amputation or paralyzation. Therefore, in this instance the primary goal is not to amplify and faithfully reproduce a myo-electric signal but to process the signal in such a way that the resultant signal may be used as an effective means for transmitting information across the man-machine interface to the assisting machine or device. When striated muscles of the body are voluntarily made to contract, electrical impulses from the central nervous system travel along nerve fibers to the muscles. The electrical impulses initiate electrical activity in the muscle fibers which in turn mechanically contract. This electrical activity of the muscles may be detected, with amplification, using metal electrodes. The signal amplitude increases as the level of muscle activity increases and is dependent upon the physiological condition of the muscle, the type of electrodes used, and the distance of the electrodes from the activity. Generally the signals are in the microvolt range but may be as large as two or three millivolts. The systems described in this paper were designed primarily for processing myo-electric potentials which are detected on the surface of the skin.
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