MENTAL STRESS OF LONG-DURATION - EMG ACTIVITY, PERCEIVED TENSION, FATIGUE, AND PAIN DEVELOPMENT IN PAIN-FREE SUBJECTS

The study examined the relationship between pain development in the sh oulder, neck, and facial regions and the EMG activity of underlying mu scles, during prolonged exposure to a mantel stressor. The subjective perception of tension and fatigue was recorded. Thirty-six subjects we re exposed to a two-choice reaction-time test for 1 hour. Electromyogr aphic (EMG) recordings were performed bilaterally over the frontalis, temporalis, splenius, and trapezius muscles. Pain and perceived tensio n were scored on a visual analog scale, and fatigue on a Borg scale. P ain development was most pronounced in the shoulder and neck region. T here was a weak tendency of those reporting pain in the shoulder regio n to generate higher EMG activity in the trapezius relative to those w ith no shoulder pain at the end of the test. No such relationship was observed for the other muscles. Perceived tension during the test was weakly related to pain and strongly related to fatigue st the end of t he test, but not to EMG level. It is concluded that the mean level of the EMG response is of little consequence for pain development during stressful conditions. It is argued that other physiological responses such as prolonged activity in low-threshold motor units. whereby the s urface EMG response can serve as a marker, can be important for should er pain originating in the trapezius muscle.