Arm and trunk posture during work in relation to shoulder and neck pain and trapezius activity

OBJECTIVE: To investigate work technique in relation to work-related shoulder and neck pain (SNP) and upper trapezius muscle activity. DESIGN: A matched pair, case-control field study of female employees with and without SNP. BACKGROUND: It has proved difficult to distinguish subjects with SNP from those without by vocational electromyographic recordings from the upper trapezius muscle. Other potential risk indicators include psychosocial factors and work technique. This study focuses on the latter. METHODS: Manual (14 pairs) and office workers (24 pairs) were recorded during a 30-min work period. Simultaneous recordings of upper trapezius activity by surface electromyography and arm and upper back postures by inclinometers were analysed. RESULTS: Cases and controls were not differentiated on the basis of arm elevation or of trunk posture in the sagittal plane. No significant correlations were found between variables averaging the muscle activity and the arm elevation over the recording period. Statistically significant correlations were, however, found between these variables when analysing recordings at high time resolution (0.2 s) and adjusting for the delay in arm elevation relative to the upper trapezius muscle activity (r = 0.43, manual group; r = 0.32, office group). CONCLUSIONS: Factors other than arm elevation probably contribute more significantly to the load in the upper trapezius muscle, and to the development of work-related SNP in work situations with moderate arm elevation. RELEVANCE: The study suggests that arm and trunk posture recordings are not a sensitive indicator of risk of shoulder and neck complaints in work with low to moderate biomechanical demands.