EMG and Biofeedback: The electromyograph (sEMG) allows readings to be taken via 3 surface sensors placed on the skin over appropriate muscles. Biofeedback EMGs are non-invasive and should not be confused with diagnostic needle style EMGs. sEMG feedback is used for general relaxation training and is the primary modality for treatment of pelvic floor muscle re-education (incontinence), headache, bruxism and temporomandibular joint problems, chronic pain, muscle spasm and partial paralysis, speech disorder or other muscular dysfunction due to injury, stroke, or congenital disorders. Physical rehabilitation through neuromuscular re-education is also an important application.
The EMG has long been a standard instrument in most physical medicine offices, as well as being utilized by clinicians as a treatment rather than a purely diagnostic instrument. Clinically, work has focused on two quite different areas; Neuromuscular Re-Education and General Relaxation/Tension reduction.
EMG Physiology: The EMG measures the amount of electrical discharge in the muscle fibers and therefore it quantifies muscle contraction and relaxation. This electrical discharge is translated into auditory and visual displays and the person can begin to notice and bring about changes in muscle tension which he/she was previously unable to do.
Since the microvoltage of EMG’s is directly proportional to the mechanical muscle contraction, it is a measure of muscle relaxation and tonus. There is a desirable level of muscle tonus which can be exceeded ( Chronic muscle tension ) or which is absent ( neuromuscular disorders ). Chronic muscle tension consumes considerable energy, leaving the person tired and fatigued.
EMG Measurement: The major placements of emg electrodes have been frontalis, trapezius and forearm. It is incorrect to assume that EMG biofeedback is synonymous with “Frontalis EMG Biofeedback” since frontalis represents only one of many possible placements. While frontalis and other foci may represent reasonable reflections of total body tension, it is entirely possible for the person to have learned to maintain low frontalis tension while holding chronically high levels in the rest of the body. It is impractical as well as inconvenient, however to use dozens of electrodes over the entire body for accurate over-all muscle tension assessment.
Recently, more work has been done with the more generalized wrist to wrist ( or even ankle to ankle ) placement. This allows a measure of upper or lower body tension respectively. One method in the wrist to wrist placement is to use a direct audio mode and have the patient reduce the sound sufficiently as to be able to detect heart rate in the audio signal. Using this relative amplitude criteria provides a built in goal in relaxation training.
EMG History, Physiology, & Measurement taken from BIOFEEDBACK Methods and Procedures in clinical practice ( 1977) written by George D Fuller, Ph.D.