The Relationship between Myoelectric Activity of Trunk Muscles and the Changes of Intervertebral Angle in Patients with Low Back Pain

THIS STUDY EXAMINED the relationship between eletromyographic activity of trunk muscles and the changes with intervertebral angles of the lumbar spine in subjects with low back pain. A comparison was also made with volunteers not complaining of low back pain. Forty-seven patients with low back pain (LBP group, L) and 45 volunteers without any complaint of low back pain (asymptomatic group, A) participated in this study. Each subject undertook radiography with three different postures (upright, maximal trunk flexion, and maximal trunk extension). Electromyography was recorded in the same positions as chosen during radiological examination. The muscle groups recorded were latissmus dorsi, erector spinae (upper portion, lower portion), abdominis rectus, and abdominal oblique. Changes of Cobb's angles were determined as the intervertebral angles at each level of lumbar spine. The changes of Cobb's angles significantly decreased with maximal flexion of trunk in the group with low back pain compared with that in the asymptomatic group. In low back pain subjects with maximal trunk flexion, the myoelectric activities of the trunk extensors significantly increased, but those of the abdominal muscles measured decreased compared with those in the group of asymptomatic subjects. In the group with low back pain with maximal trunk extension, trunk muscles measured in this study showed a smaller increment of myoelectric activities than those measured in the group of asymptomatic subjects. In the asymptomatic group, a negative correlation was shown to be significant between the changes of myoelectrical activities of the trunk extensors in the position of trunk flexion and the changes of Cobb's angles at relative lumbar locations that did not exist in the low back pain group. Different myoelectric activation of trunk muscles demonstrated in the asymptomatic subjects might affect those angles of lumbar intervertebral segments. In the group of patients with low back pain, the decrease of intervertebral angles of lumbar spine might be attributed to the inadequate electromyographic pattern of trunk. According to our results, the relationship of changes of trunk muscle activities at different postures with the changes in lumbar intervertebral angles in the asymptomatic subjects did not exist in the patients with low back pain, which might be considered as a reference during clinical evaluation for low back pain patient.