ELECTROMYOGRAPHIC SIGNAL CHANGES DURING EXERCISE IN HUMAN CHRONIC JAW-MUSCLE PAIN

Twelve individuals (2 males, 10 females) with chronic masticatory musc le pain and 11 individuals (2 males, 9 females) without, had their bit e force and surface electromyography from the right and left superfici al masseter and anterior temporalis muscles recorded before, during an d after a 30-s sustained submaximal clenching task. This task was perf ormed at 50% of the force level of each subject's maximum voluntary co ntraction (MVC) for 30 s. Brief (3 s) 50% MVC efforts were recorded at 15-s intervals, three times before and six times after the sustained clench. Each subject performed this pattern of activities three times with a 15-min rest between each trial. The centre Frequency (CF) of th e electromyographic power spectrum was calculated by fast Fourier tran sformations. The mean CF at the end of the 30-s clench and the rate of change al the CF during the clenching task were analysed between grou ps, sides and muscles. The data indicated that the masseter CF decreas ed at a significantly faster rate for the first clenching trial in the muscle-pain group. Conversely, the rate of change in the temporalis C F did not significantly differ for the two groups during the three cle nching trials. By the third trial the CF of the exercised masseter in the non-pain group exhibited a similar rate of change to that in the p ain group. This suggests that both repeated exercise and the presence of chronic inflammation increase the rate of change of the electromyog raphic signal of the contracting masseter. The mechanism underlying th is increased change is unknown.