Loading of shoulder muscles in a simulated work cycle: comparison between sedentary workers with and without...

Ten female bank cashiers with frequent neck-shoulder symptoms and ten non-symptomatic referents (matched by age, body-size and work experience) doing similar work performed a work simulation demanding attention and static holding of the arm. Surface electromyography was recorded on the upper trapezius and rhomboideus/erector spinae muscles. The static load moments of the working arm were calculated from still video pictures. No significant differences were found between the two groups in electromyographic activity on the working or on the opposite resting side, although the subjects with frequent symptoms showed greater variation in electromyographic activity. Changing the location of the task from the distance of the upper limb length and eye level to a location about 10 cm lower and 10 cm closer to the subject reduced the electromyographic activity of the trapezius muscles by 25-30%.