The interaction effect of working postures on muscle activity and subjective discomfort during static working postures and its correlation with OWAS

Methods assessing exposure to workload calculate risk scores of individual body segments which are added up to calculate an overall risk score for the whole body. However, these methods ignore interaction effects of body segments. This may lead to inaccurate assessment of risk scores of workload. The aim of the study was to examine interaction effects of shoulder flexion angle and back angle on rating of perceived exertion (RPE) and muscle activity, and to investigate the correlation between corresponding Ovako Working Posture Analysing System (OWAS) risk scores on the one hand and RPE and muscle activity on the other. The study revealed that there is a significant interaction effect of back angle and shoulder angle on muscle activity and RPE. Furthermore, OWAS seems to correlate only with back muscle activity. Thus, integration of interaction effects to ergonomic assessment methods seems to provide a higher accuracy of risk scores. This article introduces the relevance of interaction effects of body segments to the assessment of workload. The study revealed that isolated assessment of working postures ignores interaction effects. A consideration of interaction effects leads to a higher accuracy of risk scores quantifying exposure to workload.