Power spectral analysis of lumbar muscle electromyogram in chronic low-back pain patients during dynamic trunk exercise

The purpose of this study was to investigate the pattern of lumbar muscle fatigue at spinal level during repeated dynamic trunk flexion and extension exercise in chronic low-back pain (CLBP) patients and in control subjects without back pain. The authors used a lumbar extension machine which is designed to isolate lumbar extension functions. The electromyogram (EMG) signal from erector spinae muscles at lumbar 1 (L1), L3 and L5 spinal level was detected by surface electrodes. Subjects were required to perform one set of variable resistance lumbar extensions through a 72° range of motion (ROM) with a weight load that allowed 13 repetitions of fatigue contraction. Median frequency (MF) of the EMG power spectrum was analyzed to compare fatigue. The experimental results indicated: (1) each lumbar muscle has a characteristic initial MF (IMF); (2) the IMF of each lumbar level showed no significant difference between the CLBP and control groups; (3) there were significant differences in the decreasing ratio of MF between L1, L3 and L5 in both groups; (4) the decreasing ratio of MF at L5 in the CLBP group was significantly higher than the control group