EMG of Electrically Stimulated Muscles

This chapter addresses stimulation techniques, the issue of the stimulation electrode positioning, motor unit (MU) activation order, and spinal involvement in electrically elicited contractions. Two stimulation techniques are commonly used: bipolar, and monopolar stimulation. The differences between these two methods concern the geometry and relative position of the stimulation electrodes. Surface electromyography (sEMG) signals can be detected during selective electrical stimulation of a nerve branch or of a motor point of a muscle. The resultant sEMG signal is a compound motor action potential (CMAP), also termed as M-wave. Since the M-wave represents the sum of the potentials of the concurrently activated MUs, its change is generally assumed to reflect changes either in the number or in the sarcolemmal properties of activated MUs. Neuromuscular electrical stimulation (NMES) combined with sEMG isolates the contributions of peripheral fatigue because it gives the experimenter control of MU firing frequency and recruitment.