Some differences of the electromyographic erector spinae activity between normal subjects and low back pain patients during the generation of isometric trunk torque.

A method of evaluation of the isometric trunk extension effort and integrated electromyographic activity of the low back muscles during straight position under goniometric control was used. In order to evaluate the paravertebral muscle activity, two pairs of bipolar surface EMG electrodes have been attached bilaterally over the erector spinae muscles at a lateral distance of 3 cm at the level of L3 spinal processus. 40 patients with low back pain and 40 normals were involved to participate in this study. EMG activity and strength was higher in normals than in patients. However, this distinction was statistical significant in strength, and nonsignificant in EMG activity. Patients showed relatively higher, asymmetric and more expressive in the painful side integrated electromyographic activity under maximal and submaximal contraction. Strength/EMS relationship was close to linear in normals, whereas in patients this proportionality was nonlinear. Therefore in patients a smaller tension correlated with relatively higher muscle activity.