An experimental evaluation of psychophysical criteria for repetitive lifting work

Two experiments were performed to test the reliability and validity of psychophysically determined maximum acceptable workloads for setting lifting standards. The perceived workload in a repetitive diagonal lifting task was found to be a positively accelerated function of the weight lifted and of the work pace respectively. A twofold increase in objective workload resulted in a four- to fivefold increase in perceived workload. This relation was independent of previous occupational experience of lifting work. The psychophysically assessed maximum acceptable workloads for this type of lifting task appeared to be satisfactorily reproducible when subjects had to adjust work pace or when they were left free to adjust both the weight and the work pace. However, the results raised several questions concerning the applicability of the psychophysical assessment of maximum acceptable lifting work. Slight changes in the instructions given to the subjects had a definite effect on the selection of workloads. Furthermore, the workloads selected by subjects with previous occupational experience of lifting work - i e, warehouse workers - were systematically lower than those selected by subjects without such previous experience - i e, office employees. At the same time, the warehouse workers rated perceived exertion higher than the office employees, indicating that previous occupational experience of lifting work enhanced the subjective assessment of physical effort. There were no consistent relations between the workloads found acceptable by the subjects and their physical characteristics and performance capacity.