Torso muscle EMG profile differences between patients of back pain and control.

BACKGROUND Electrophysiological criteria that identify and characterize low back pain can lead to better understanding of the affliction and possibly aid in its treatment. METHOD Nineteen male and 22 female subjects with chronic back pain, without lumbar radiculopathy; and 30 male and 33 female control subjects with no history of low back pain in the last 12 months, were recruited into the study. All subjects flexed, extended, laterally flexed, flexed anterolaterally and extended posterolaterally isometrically to 20% and 100% of their maximal voluntary contraction (MVC). Additionally, patients were asked to do these activities to their pain threshold levels and control subjects to 60% maximum voluntary contraction. Surface electromyograms (EMG) were recorded from lumbar erectores spinae, external obliques and rectus abdominis bilaterally. The electromyogram was subjected to magnitude, Fast Fourier Transform, and wavelet analyses. The median frequency and frequency bands were calculated with their power. The wavelet decomposition was done and a logistic discriminate analysis was carried out to classify patients and normal controls. FINDINGS The normalized peak electromyograms of patients were significantly greater than controls (P<0.01). The muscle conduction velocity was not disturbed by pain. Significant differences were found in total power between patients and controls (P<0.01). The analysis correctly classified patients and controls 65% and 98% of the time, respectively at 20% MVC, 95.1% (patients) and 86.8% (controls) at pain threshold/60% MVC, and 74.3% (patients) and 86.4% (controls) at pain tolerance/MVC (P<0.05). INTERPRETATION The surface electromyography can be used in discriminating chronic low back pain patients and controls. This would be an objective test over and above other subjective tests, such as pain provocation.