Surface Electromyography (sEMG) is the electrophysiological technique for quantifying motor activity (muscle contraction) in specific muscle groups as determined by electrode placement. A muscle contraction involves stimulation of a group of fibers controlled by the motor neuron. This combination of motor neuron and group of muscle fibers is known as the motor unit. The number of fibers controlled by the motorneuron correlates highly with the function of the muscle: large muscle fiber to motor neuron ratios are found in muscles controlling gross movement, while smaller muscle fiber to motor neuron ratios are found in muscle groups responsible for finer movements, as in the hand.

sEMG is currently utilized by researchers and medical practitioners alike, including physical therapists, medical doctors, chiropractors, osteopaths and psychologists. Ergonomics researchers are currently using sEMG in validating the potential of certain input devices such as keyboard and mice for causing Carpal Tunnel Syndrome. Clinical applications include neuromuscular re-education, disability evaluation, evaluation of various movement disorders and documentation of soft tissue injury.

Currently, the two areas of greatest interest are the measurement of muscles during movement (attached electrode dynamic evaluations) and spectral analysis of sEMG during isolated isometric contractions. Both show great promise in evaluating low back pain. Specifically, the Flexion-Relaxation Response utilizing the attached electrode dynamic technique of measurement has been evaluated thoroughly and found to be quite robust. Additionally, we at PBI have designed the static sEMG, with its high quality torso graphs and pre-post comparison tests, to be a very powerful patient education tool.