Changes in paravertebral EMG spectrum parallel to strength increases after rehabilitation in chronic low back pain patients

The aim of this preliminary report was to identify parameters related to functional improvement in healthy subjects and in patients with chronic low back pain (LBP) undergoing an intensive rehabilitation programme. Four healthy controls and four chronic LBP patients were evaluated before and after a four-week rehabilitation programme. Dynamic and static strength tests, namely sustained isometric contractions, and trunk flexion-extension movements were performed in conjunction with surface electromyographic (EMG) measurements. Significant pre-rehabilitation differences were found between the two groups. Measured forces and the ratio between EMG amplitude values during extension and during flexion changed significantly in LBP patients immediately after rehabilitation. No significant changes were found in the control subjects after the rehabilitation programme. After rehabilitation, the slope of decay of the median frequency of the EMG power spectrum at L4 level, during a 60-second isometric submaximal (60% MVC) contraction, decreased significantly ( p < 0.02), indicating a lower fatigue level.