Electromyographic recordings of 5 types of low back pain subjects and non-pain controls in different positions.

Surface EMG recordings of bilateral paraspinal muscle tension were measured on 207 subjects (29 non-back pain controls, 20 individuals with spondyloarthritis, 52 with intervertebral disk disorders, 66 with unspecified musculoskeletal backache, 17 with some combination of the above 3 groups and 23 subjects with other types of back pain, including unknown, scoliosis and psychogenic) in 6 positions: standing, bending from the waist, rising, sitting with back unsupported, sitting with back supported and prone. Results of both individual and group analyses revealed a significant main effect of diagnosis. Post hoc analyses (Duncan's) revealed controls to have significantly lower overall EMG levels than the intervertebral disk disorders and unspecified musculoskeletal backache groups. A significant diagnosis by position interaction was observed. Analysis of simple main effects revealed this to be due primarily to control subjects during the standing position having lower EMG levels than all other groups, and intervertebral disk disorder subjects having higher EMG levels than all other groups during the supported sitting position. The importance of clearly defined diagnostic categories in low back pain research and the utility of measuring subjects in various positions are discussed.