Force, posture and repetition induced discomfort as a mediator in self-paced cycle time

Musculo Skeletal Disorders (MSDs) especially those of the upper limb are a highly prevalent occupational health problem in industry incurring substantial costs. A link has been shown between physical risk factors and the causation of MSDs, in particular, high levels of force, deviated postures and repetitive movements. These have each been associated with increased operator discomfort in industry and laboratory experiments. Ergonomic interventions reducing the effects of these risk factors have been demonstrated to lower discomfort but also increase productivity. There are many case studies which have reported on the relationship between physical risk factors, associated discomfort and productivity, but few attempts have been made to investigate the relationship and model it. A laboratory study was conducted to test the hypothesis that physical risk factors effect discomfort and that this in turn effects productivity. Participants performed repetitive grip exertions involving combinations of three levels of grip force (10, 20 and 30% MVC), repetition (10, 15 and 20 repetitions per minute) and wrist posture (50% flexion/extension and neutral). Treatments were performed for 10 min after which the participants were instructed to adjust the cycle time to a self-selected-pace (the productivity measure) for the remaining 10 min. Analysis of Variance (ANOVA) was performed on the data and the results indicated that each of the main factors had significant effects on discomfort at 10 min. Self-pace cycle time was significantly affected by force and posture. Correlation and regression analysis revealed a strong relationship between discomfort and self-pace cycle time. Path analysis revealed that discomfort was a mediating variable in the relationship between the primary risk factors and self-paced cycle time. These data indicate that reducing discomfort by reducing risks associated with high forces and deviated postures could help improve productivity for self-paced-work. Relevance to industry: This study investigated the relationship between discomfort and parameters of productivity for a simulated task. The results indicate that reducing exposure to force and posture effects should improve productivity in repetitive work. (C) 2010 Elsevier B.V. All rights reserved.