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Relation between Whole-Body Postural Discomfort and Body-Part Postures for Working Postures of Automobile Assembly Tasks

Observational methods have been widely used for identifying posture-related risks in industry. In those methods, a single score of postural load for a working posture is required for evaluating the level of corrective actions, on the basis of each body-parts stressfulness evaluated. However, most existing methods have transformed stressfulness for several joints into a postural load based on subjective judgments of ergonomic experts, not on an objective basis. In this study, the relationship between body-part postural load and whole-body discomfort for working postures was investigated. A laboratory experiment was conducted to evaluate static postures frequently assumed during the automobile assembly tasks, based on perceived discomfort. The results showed that the postural load was strongly associated with the combination of discomfort for non-neutral joint postures. The more joints severely deviated from neutral position were involved in a working posture, the higher level of the whole-body postural discomfort was imposed. In a regression analysis, the relationship was quite well fitted with a linear model, in which shoulder motion was found to be the most affecting factor on the whole-body postural stresses. The linear relationship is expected to be useful for better understanding adverse effect of joint motions on a whole-body posture.