Relationship between trapezius load and the incidence of musculoskeletal illness in the neck and shoulder

A relationship between m. trapezius load measured by electromyography (EMG) and the incidence of musculoskeletal illness in the neck and shoulder regions, was investigated both for assembly workers and VDT operators. For assembly workers, the static trapezius load (probability 0.1 of the amplitude probability distribution function, APDF) was significantly reduced from 4.3% MVC (Maximum Voluntary Contraction) to 1.4% MVC as a group median value after an ergonomic adaptation of their work places. Musculoskeletal sickleave was significantly reduced from 22.9 days to 1.8 days as a medium duration per-man-labour year for the same group.

Three groups of VDT operators were examined in terms of trapezius load and pain intensity and duration before and after an ergonomic intervention. All groups reported significant less intensity or duration of pain either in the neck or in the shoulder regions after the intervention. The trapezius load was reduced for all groups post vs. prior intervention. This reduction was measured in terms of a decrease in the static level of APDF and an increase in the number of periods per minute and total duration of muscle activity below 1% MVC. The results from this study indicate that the trapezius load may be a predictor for development of musculoskeletal illness in the neck and shoulder regions.