A psychophysical study of the effects of load and frequency upon selection of workload in repetitive lifting.

Abstract

Human capabilities in manual materials-handling activities may be influenced by a number of task variables. The psychophysical method of Snook (1978) was used to determine the effects of load and lifting frequency upon workloads selected by eight male soldiers. The subjects repeatedly lifted and lowered a box (38 × 55 × 24 cm) to and from a platform set at 40% stature for 10 minutes and either adjusted the load, or the lifting frequency, or a combination of both variables in order to select a workload which they considered to be a maximum acceptable workload (MAWL) for a work-period of one hour. When the lifting frequency was adjusted, the mean MAWL was 94·5 kg m min −1 (S.D. 28·4). This was significantly greater (P ≤ 0·05) by 27% than when the load alone was adjusted (74·3 kg m min −1, S. D. 23·3). Control of both variables together produced a MAWL of 76·5 kg m min −1 (S. D. 24·1) which was similar to that selected when the load alone was adjusted. When the soldiers lifted and lowered their selected work...