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.
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