Mathematical models for determining comprehensive manual handling limits for lowering, pushing, pulling, and carrying were developed. The goal of such manual handling guidelines was to protect workers against occupational low back disorders. A three stage process was applied to the development of manual handling guidelines for both men and women. In the first stage, previously published psychophysical data were used to develop the discounting factors and recommended load capacities of the models. The psychophysical data consisted of the maximum acceptable weights and forces for various proportions of the male and female population engaged in lowering, pushing, pulling, and carrying tasks. The discounting factor multipliers were based on task and personal characteristics. In the second stage, the recommended load capacities were modified via biomechanical lifting equivalent criteria. For lowering and carrying tasks, biomechanically derived base weights tended to be lower than psychophysically derived base weights, whereas for pushing and pulling tasks, biomechanically derived base weights tended to be higher than psychophysically derived base weights. In the third stage, the discounting factors were validated using physiological criteria consisting of energy expenditures and fatigue limits. The load capacities developed according to the above method were lower than previously established load capacities. The authors conclude that physiological and biomechanical stresses together result in the overall measure of manual handling task acceptability for tasks in which the compressive forces are critical. Validation of these models in the industrial setting is needed.
NIOSH-Author; Mathematical-models; Quantitative-analysis; Physical-stress; Manual-materials-handling; Manual-lifting; Ergonomics; Body-mechanics; Physical-capacity; Physiological-fatigue; Physiological-measurements; Work-capacity; Musculoskeletal-system;
Author Keywords: Manual Materials Handling; Biomechanics; Work Physiology; Psychophysics