Electromyographic functional analysis of the lumbar spinal muscles with low back pain.

The lumbar paraspinal muscles were examined by surface electromyography (EMG) in 22 patients with low back pain and 22 healthy volunteers. Surface electrodes were placed bilaterally on the lumbar multifidus and longissimus muscles at the level of the spinous process of the third lumbar vertebra. Kinesiologic EMG was recorded, in standing resting position, during the following trunk motions: trunk forward flexion and extension, lateral bending and axial rotation. No muscular activity was observed in the full trunk flexion position in the control group. In contrast, continuous muscle activity was observed in the low back pain group. On axial rotation, an intermuscular time lag was observed at the beginning of the motion in the control group. In the low back pain group, there was no such time lag. Paraspinal muscle activities restricted lumbar range of motion, and protect from injury for movement. This suggests their role as stabilizers.