The use of electromyography to quantify muscle pain

This study was designed to determine the feasibility of using electromyography (EMG) to quantify muscle pain in patients suffering from chronic myofacial pain dysfunction (MPD). Ten patients were carefully selected to include those having mild to severe pain, but not any major psychological or other physiological dysfunction. Measurements of perceived pain and EMG frequency and amplitude were recorded before and after standard analgesic therapy. EMG recordings were collected bilaterally from the masseter and anterior temporalis muscles during the resting, swallowing, clenching and chewing modes of activity. Multiple regression (R) analysis indicated that changes in perceived pain are correlated with changes in the EMG and can be determined by using the following formula: delta P = (delta F) (0.405) + C where P = perceived pain level, F = EMG frequency, and C = 1.533. By computing the Phi coefficients, the highest correlation between EMG recordings and subjective pain ratings was demonstrated in the resting mode. In this mode, 64% (multiple R = 0.80) of the variance in perceived pain difference scores from pre- to post-therapy tests could be determined. A significant relationship exists between the change in perceived pain and the EMG (t = 2.525, p less than 0.05), whether pain levels increase or decrease. The implementation of this method to quantify expected changes in pain due to muscle spasm in uncomplicated individuals is discussed.