Surface electromyography of the paravertebral muscles in patients with chronic low back pain

Kramer M, Ebert V, Kinzl L, Dehner C, Elbel M, Hartwig E. Surface electromyography of the paravertebral muscle in patients with chronic low back pain. Objective To investigate the differences in the electromyographic signals of patients with chronic low back pain (CLBP) and healthy subjects. Design Cross-sectional study with a matched-pair design. Setting University hospital. Participants Thirty-one patients with CLBP and 31 healthy, matched-pair controls. Interventions The mean rectified surface electromyographic amplitude and muscle strength were measured during maximal voluntary contraction (MVC). During an endurance test at 60% of MVC, the electromyographic parameters of the 2 groups were compared. Main outcome measure Electromyographic measuring of local fatigue, which can be described with changes in the median frequency or by a different parameter of the power spectrum called frequency banding. Results The strength measurement revealed a deficiency of 40% in the patients and a deficit in the electromyographic amplitude of approximately 60%, compared with the control group. By pairwise comparison, the decrease in the median frequency during the endurance test was greater in the control group. In the frequency banding of the power spectrum, local fatigue was less pronounced in the CLBP patients in pairwise comparison. Conclusions The back muscles of CLBP patients appear to be less fatigable than those of controls. The results can be explained by morphologic changes, but influences such as pain, avoidance of pain, and deconditioning, need to be considered when the results are assessed.