A CASE-CONTROL STUDY OF TRAPEZIUS MUSCLE-ACTIVITY IN OFFICE AND MANUAL WORKERS WITH SHOULDER AND NECK PAIN AND SYMPTOM-FREE CONTROLS

A case-control study with matched pairs was initiated to investigate t he relationship between shoulder-neck complaints and activity in the u pper trapezius muscle. The matching was done so that the physical dema nds from work (external exposure) were equal for both the case and the control. Each pair was also matched for gender, age, working hours, a nd employment time. Male (n = 18) and female workers (n = 78) employed in both manual and office work were included. Muscle activation level s and pause patterns during work and muscle activity during tests of a ttention, coordination, and rest were recorded by surface electromyogr aphy. The results showed consistent associations between pain and sign s of increased activation of the upper trapezius for the cases in the manual group. No such associations were observed in the office group. The results are consistent with the hypothesis that muscle activation patterns may in some instances, but not in all, explain why some worke rs develop pain while others do not in work situations where the physi cal demands are similar.