The effect of experimental jaw muscle pain on postural muscle activity

The purpose of this study was to examine whether tonic muscle pain of an intensity at least as great as that reported by the majority of chronic muscle pain patients causes an increase in postural electromyographic activity of the affected musculature. Twenty young adults volunteered for experiments, knowing that they involved experimental pain. We chose a controlled, two-period crossover and repeated measures design involving four experimental conditions: (1) baseline 1, (2) tonic experimental muscle pain, (3) sham pain, and (4) baseline 2. Subjects were randomly assigned to one of two sequential orders that differed with respect to whether tonic pain preceded sham pain or vice versa. At the within-subject level, the condition (baseline 1, sham pain, tonic pain, baseline 2) had a statistically significant effect on mean rms electromyographic activity at all four recording sites. We found that postural activities at all four recording sites, left/right masseter and left/right anterior temporalis were statistically different from baseline 1 and 2 during tonic pain (P < 0.004, s.; P < 0.024, s.). However, postural activities during tonic pain and sham pain were not significantly different from each other (P < 0.493, n.s.). We concluded that our data do not support the hyperactivity model which assumes a re-enforcing link between pain and muscle hyperactivity.