Strategies of load tilts and shoulders positioning in asymmetrical lifting. A concomitant evaluation of the reference systems of axes

Abstract

Objectives. To evaluate two handling factors on asymmetry of posture and efforts and to evaluate different reference systems of axes on the characterization of asymmetry. Design. Ten novice workers performed three tasks evaluated for the effects of load tilting (tilts vs no tilts) and shoulders positioning (non-parallel vs parallel to the ground). Specific comparisons were made using three referential systems. Background. Box handgrips/tilting and body posture are factors differentiating expert and novice workers which present a potential for reducing asymmetries. The literature also suggests that different conclusions may be reached about asymmetry with different systems of axes. Methods. Net 3D moments at L5/S1 were obtained from two force platforms, four video cameras and inverse dynamic analyses using three reference systems of axes (trunk, pelvis, and joint). Results. Tilting the load presented clear advantages of reducing the duration and trajectory of efforts, better positioning the load and reducing knee flexion, peak trunk extensors and mechanical work on the load. The maintenance of the shoulders parallel reduced asymmetries of posture and efforts but the results were affected by the type of reference system of axes chosen. Conclusions. Box tilting and shoulders positioning should be considered in the reduction of risk factors. More research is needed to define referential systems and characterize asymmetry. Relevance Box tilting and shoulders positioning appear to be two fundamental elements to take into account in the formation programs based on prevention of risk factors. The importance of asymmetry among the risk factors emphasizes the need for better characterization of this risk.