Secular changes in psychophysically determined maximum acceptable weights and forces over 20 years for male...

The most frequent and expensive cause of compensable workplace injuries loss is manual material handling (MMH). In an attempt to minimise these losses, refinement of existing MMH guidelines is a component of redesigning high risk MMH jobs. In the development of the present MMH 1991 guidelines (Snook and Ciriello 1991), maximum acceptable weights (MAWs) and forces (MAFs) were derived from studies conducted in a 21 year time span before the above publication date. The question arises whether the present generation of workers have the same psychophysically determined weights and forces as those reflected in the guidelines. Therefore, the present study investigated whether secular changes had occurred in key MMH tasks in trials performed by present day local industrial workers. A total of 23 male industrial workers performed 20 variations of lifting, lowering, pushing, pulling and carrying tasks. A psychophysical methodology, identical to that of the authors' previous experiments, was used whereby the subjects were asked to select a workload they could sustain for 8 h 'without straining themselves or without becoming unusually tired, weakened, overheated or out of breath'. The results revealed that MAWs of lifting, lowering and carrying averaged 69% of the guideline values. MAFs of pushing and pulling showed less of a drop, averaging 82% and 94% respectively for initial and sustained forces. The results also indicated that the effects of the variables frequency, height, lifting vs. lowering, pushing vs. pulling were similar to earlier reported results, even though the absolute weights or forces were lower. It was concluded that consideration to change existing guidelines, reflecting this new psychophysical set point, may be appropriate if these significant performance decreases are confirmed in other locations, with greater subject numbers, and by other investigators.