Theories of work-related musculoskeletal disorders: Implications for ergonomic interventions

There are a growing number of theories and models that describe how workrelated musculoskeletal disorders (WMSDs) are caused. Nine of these theories and models are described, compared and contrasted. The models are then integrated to form a composite model that incorporates the various paths and mechanisms that have been proposed. This composite model illustrates the complexity of WMSD aetiology by describing 35 proposed pathways between the 12 major constructs that have been proposed in previous models. This complexity helps to explain difficulties encountered in interventions to control WMSDs. Several implications for ergonomic intervention research that are based on the integrated model are considered, including suggestions for measurement, treatment and analysis. Specific suggestions for measuring multiple outcomes, measuring and analysing possible confounders and selecting appropriate controls for known risk factors are discussed.