Purpose: Previous studies have suggested that high frequencies of shoulder and neck complaints in dental hygienists mainly were due to longstanding, low-level static load of the neck and shoulder muscles. The purpose of the present study was to make continuous recordings of myoelectric signals from the shoulder muscles of dental hygienists in order to assess static load.
Methods: Myoelectric signals were recorded from the right trapezius muscle of 10 Swedish dental hygienists during half of a normal working day. A portable system for collection and on-line processing of myoelectric signals was used. Signal parameters were obtained, indicating muscular load, fatigue, pause frequency, and pause duration, respectively. All measurements were referred to a resting value and a reference contraction value established with the hand loaded with a 0.5 kg weight at the beginning of the recording session.
Results: A static load of 50 to 100% of the reference contraction (0.5 kg hand load with raised arm) was found in the trapezius muscle. The median load for the whole group was 57% of the reference level. Group data analyses of frequency EMG seldom showed significant fatigue. At individual levels, however, it was possible to identify localized muscle fatigue and relate it to a specific work task. There were many short pauses with a duration of 1 to 2 seconds, but an almost total lack of pauses of a duration longer than five seconds.
Conclusions: Individual dental hygienists exhibited significant muscle fatigue that might be related to development of work related myalgias of the shoulder muscles. Future study of muscle patterns and dental hygiene tasks may lead to improved work designs and patterns for dental hygienists.