The Effects of Distance on Psychophysically Determined Pushing and Pulling Tasks

Abstract

The most frequent and expensive cause category of compensable loss is manual material handling (MMH). in an attempt to minimize these losses, refinement of existing MMH guidelines is a component of redesigning high risk MMH jobs. in the development of our present MMH guidelines (Snook & Ciriello, 1991), maximum acceptable forces (MAFs) of pulling were assumed to respond similarly to pushing at longer distances. The purpose of this experiment was to investigate the effects of 7.6m and 15.2m distances on both initial and sustained MAFs of pushing and pulling at a frequency of 1 min⁻¹. A psychophysical methodology was used whereby the subjects were asked to select a workload without “straining themselves or without becoming unusually tired, weakened, overheated or out of breath.” Subjects worked 40 min at each push or pull task within a 4-hour test that included other MMH tasks. The results revealed that initial and sustained MAFs and task time were not significantly different between pushing and pulling at the 7.6m distance. However, at the 15.2m distance, initial MAF of pulling was significantly lower and task time was significantly longer compared to pushing. Sustained MAF was not significantly different at 15.2m. It was concluded that our existing guidelines present an accurate estimate of MAFs at the longer pull distances.