EMG Power Spectrum of Lumbar Back Muscle in Chronic Low Back Pain Patients

Sohn, Min Kyun; Yoon, Yeo Sam; Jun, Kae Ho

Abstract

Surface electromyogram in the lumbar paraspinal muscles was studied to evaluate back muscle impairment in twenty chronic low back pain patients and twenty control subjects. Turns-amplitude and power spectrum analysis of electromyographic signals were performed at different force levels during fatigue from sustained isometric contraction and recovery from fatigue in trunk extensor muscles. Results indicated that with increasing force level mean amplitude and Root Mean Square (RMS) values were increased, but mean and median frequencies increased initially until 20% Maximal Voluntary Contraction (MVC) and decreased tendency after then. Turns, mean amplitude, RMS, mean and median frequencies were all higher in control subject than those of low back pain patients. During sustained isometric contraction at 70% MVC, mean and median frequencies were linearly decreased, and the slopes were steeper in the patients group. Mean amplitude and RMS value showed decreased tendency during fatigue. During recovery from fatigue turns, mean and median frequencies increased especially in the first 3 minutes and nearly completely recovered in the 7~8 minutes in both patients and control groups. Therefore the mean amplitude and RMS value could be used as indicators of the level of muscle contraction and the mean and median frequencies reflect well the muscle fatigue in paralumbar muscle. These results validate the use of surface EMG spectral parameters as an objective measure of back muscle impairment in chronic low back pain patients.