**1. Introduction**

The Electromyography (EMG) is a neurophysiological technique for examining the electrical activity of skeletal muscles. The source of electrical signal in EMG is the muscle membrane potential. The muscle fibers innervated by the axonal branches of a motor neuron form a motor unit (MU). The muscle fibers of each motor unit are intermingled with fibers of other MUs [1]. The summation of action potentials of MUs is called motor unit action potential (MUAP) [2]. The biosignal recorded from a muscle or its fibers reflects the anatomical and physiological properties of the motor system. As such, EMG recording and analysis are powerful neuro‐ physiological techniques that can be employed to: a) identify the health status of the motor system; b) localize and typify peripheral and central abnormalities and lesions; c) determine the temporal course and the severity of motor system abnormalities, and d) determine and evaluate the effectiveness of treatment strategies.

Muscle activity can be detected during resting state or during voluntary movement. In addition, induction of compound action potential (CMAP) and motor evoked potential (MEP) can be obtained by means of peripheral nerve stimulation (PNS) and cortical stimulation, respectively. While PNS provides measurement of integrity of the peripheral motor system, cortical stimulation through techniques such as Transcranial Magnetic Stimulation (TMS), permit examining the integrity of the corticospinal tract.

Furthermore, the value of EMG recording as an Intraoperative neuromonitoring method has been described since the late 1970´s [3]. To date, EMG recording is a useful technique to prevent neurological damage during diverse surgical procedures.

© 2013 Wu et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Wu et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
