J Manipulative Physiol Ther. 2001 Jul-Aug; 24(6): 402-6.

Effects of a mechanical pain stimulus on erector spinae activity before and after a spinal manipulation in patients with back pain: a preliminary investigation.

Lehman GJ, Vernon H, McGill SM.

University of Waterloo-Canadian Memorial Chiropractic College Research Clinic, Faculty of Applied Health Sciences, University of Waterloo, Toronto, Ontario, Canada. gregorylehman@hotmail.com

BACKGROUND: Several recent studies in animal models of spinal pain have shown changes in sensory processing and in reflex muscular responses. One group of researchers reported consistent electromyographic responses in the paraspinal muscles of healthy men after spinal manipulation, and they speculated that such responses may underlie some of the observed clinical effects of spinal manipulation (namely, reduction in pain and muscular hypertonicity). OBJECTIVES: To determine whether a painful mechanical stimulus applied above a spinous process influences paraspinal electromyographic amplitude and whether this response is modulated by a spinal manipulation. STUDY DESIGN: Analytic cohort with a convenience sample in a research clinic. METHODS: Seventeen subjects with back pain (9 men and 8 women) were recruited. Electromyographic signals were recorded from the paraspinal musculature during the following procedures before and after manipulation: quiet stance and prone during the application of a mechanical pain stimulus. A 2-way repeated-measures analysis of variance was used to compare the effect of the force application on electromyographic amplitude. A second 2-way repeated-measures analysis of variance investigated whether the muscular response to a painful stimulus at either segment was influenced by the manipulative procedure. RESULTS: A statistically significant increase in bilateral electromyographic activity was observed at the painful motion segment; however, no such statistical increase occurred at the segment that was not painful. It appears that manipulation results in a decrease in bilateral local electromyographic activity in the painful motion segment during the application of the mechanical stimulus; however, a statistically significant decrease was not found in the control segment. It was also found that while the subjects were quietly standing, the left erector spinae at a painful segment was the only muscle group to show significant differences before and after manipulation. CONCLUSION: This study suggests that motion segments identified as a problem in subjects with chronic low back pain have an exaggerated local muscular response to a painful stimulus compared with that observed in problem segments. In addition, spinal manipulation appears to attenuate the electromyographic response to a painful stimulus.