Acceptable muscle load on the neck and shoulder regions assessed in relation to the incidence of musculoskeletal sick leave: Implications for human‐computer interaction

A threshold level for acceptable load on the musculoskeletal system of the neck and shoulder regions was explored by studying comparable groups of female workers with different development of musculoskeletal sick leave in these areas. The load on the neck and shoulder was assessed by recording electromyography (EMG) from m. trapezius (descending part). The quantitative analysis of the trapezius load was carried out by calculating the number and total duration of periods below 5% MVC (Maximum Voluntary Contraction), 8% MVC, and 10% MVC. To relate acceptable musculoskeletal load to health criteria such as acceptable limits for development of musculoskeletal illness in a group of workers, the incidence of musculoskeletal illness for the comparable groups was also compared with a control group of female workers without a continuous work load. Two groups of workers had a development of musculoskeletal sick leave, which was approximately the same as the incidence of such illness for the control group. The trapezius load for these groups was below 5% MVC for about 40% of the working time. By comparing the groups of workers with different development of musculoskeletal sick leave, the trapezius load differed only for load levels below 5% MVC; increasing duration of load levels below 5% MVC was associated with lower incidence of musculoskeletal sick‐leave. The results indicated that trapezius load below 5% MVC was important to reduce the incidence of load‐related musculoskeletal illness.