Relationships between strength of low back muscle contraction and reported intensity of chronic low back pain.

The electromyographic patterns produced by recording the left and right paraspinal muscles of subjects while in motion (bending and rising) and still (standing upright, sitting supported and unsupported, and prone) were contrasted for people with: 1) no history of back pain; 2) past episodes of low back pain but currently pain free; and 3) chronic low back pain with various diagnosed etiologies. Each of the 83 individuals recorded during episodes of low back pain produced a unique pattern of muscle contraction which was relatively stable between weekly recording sessions. In every case, at least one of the six positions showed elevated contraction levels significantly above that of the 15 subjects with no history of back pain and the 28 with no current back pain. For nine of the eleven subjects who reported changes in pain intensity between recording sessions, a clearly positive correlation occurred between the reported intensity of pain and the level of contraction in the one position most different from the reference group. No diagnostic subgroup of low back pain subjects produced a single unique pattern. Furthermore, no single aspect of the EMG signal, such as bilateral asymmetry, had predictive value for any individual subject. Our recordings did not differ with respect to diagnostic category so further research will have to be done to determine whether the diagnostic categories currently in use do not fit the physiological bases for the problems and/or whether prolonged abnormal levels of muscle contraction eventually produce problems such as disc displacement.