Trunk muscle recruitment patterns in patients with low back pain enhance the stability of the lumbar spine

Study Design. A comparative study of trunk muscle recruitment patterns in healthy control subjects and patients with chronic low back pain was conducted. Objective. To assess trunk muscle recruitment in patients with low back pain. Summary of Background Data. Conflicting evidence has been reported on the level and pattern of trunk muscle recruitment in patients with low back pain. The disparities can be explained partly by methodologic differences. It was hypothesized that trunk muscle recruitment patterns may be altered in patients with low back pain to compensate for reduced spinal stability. Methods. For this study, 16 patients with low back pain and 16 matched control subjects performed slow trunk motions about the neutral posture and isometric ramp contractions while seated upright. Ratios of electromyographic amplitudes and estimated moment contributions of antagonist over agonist muscles and of segmentally inserting muscles over muscles inserting on the thorax and pelvis only were calculated. In addition, model simulations were performed to assess the effect of changes in muscle recruitment on spinal stability. Results. The ratios of antagonist over agonist, and of lumbar over thoracic erector spinae electromyographic amplitude and estimated moment contributions were greater in the patients than in the control subjects. The simulation model predicted that these changes would effectively increase spinal stability. Conclusions. Trunk muscle recruitment patterns in patients with low back pain are different from those in healthy control subjects. The differences are likely to be functional with respect to enhancement of spinal stability in the patients.