Trapezius muscle load as a risk indicator for occupational shoulder-neck complaints.

Upper trapezius muscle activity was quantified by electromyographic (EMG) recordings using surface electrodes to study occupational muscle load as a risk indicator for the development of shoulder-neck complaints. Thirty-nine female production workers and thirty-two female office workers showed much larger interindividual differences than the mean difference in muscle activity between the two groups. By comparison with the production workers, the muscle activity patterns of the office workers were characterized by more short pauses and a lower static load. The median load level was similar for the two groups. For the office workers, but not for the production workers, weak correlations were found between symptoms of pain in the shoulder-neck region and some of the EMG parameters (static level and frequency of micropauses > 0.6 s. Current techniques for measuring shoulder muscle load by EMG recordings seem inadequate as screening methods to predict future risk of development of muscle pain symptoms.