Theoretical basis for general mixed object handling equations based on mechanical work required

Background: Traditionally, researchers concentrated on the analysis of lifting demands in industry. The assessment of mixed activities has been limited. Objective: The objective of this research is to develop a mixed object handling index (MOHI) for the analysis of the physical demands of combined pushing, pulling, lifting, lowering and carrying activities. Methods: A sequence motion model was formulated for mixed activities on the basis of the total mechanical work required, supplemented with stress coefficients to account for additional task difficulties. Results: As expected, the mixed object handling index yielded higher values than the NIOSH lifting index as a function of different task parameters. In addition, the effects of distance parameters on MOHI were more sensitive than those of angle of rotation (for pushing/pulling and carrying) and vertical height at the origin of lift/lower. Conclusions: The methodology proposed in this research can be used as a framework for the assessment of mixed activities in industry, particularly for cumulative work and peak loads.