Electrical activity in muscle pain

Abstract

The concept of muscle pain-spasm-pain vicious cycle has been challenged on the basis of inability to find electrical activity in the presence of palpable changes in fibrositic muscle. We produced muscle pain in the wrist extensor and paravertebral muscle groups of seven healthy subjects by injection of hypertonic saline (0.3 ml of 6% NaCl solution). The time course of the integrated muscle action potentials, roughly paralleled the time course of the developed pain in all but one subject for each muscle group. EMG recordings were made on one subject using both surface electrodes with amplifier sensitivity of 10 muV/cm and needle electrodes with an amplifier sensitivity of 100 muV/cm. Sequential recording showed clear evidence of electrical activity from the surface electrode and high sensitivity whereas the combination of the needle electrode with lower sensitivity showed no electrical activity whatever. We conclude that even mild muscle spasm is accompanied by muscular hyperactivity which can be evaluated by appropriate EMG techniques. There appears to be no reason to challenge the widely accepted concept of pain-spasm-pain as stated by Travell, Rinzler and Herman.