Abstract
This study investigated the effect of three different lifting instruction sets on the psychophysically selected loads. The instruction sets corresponded to three different load limit concepts: maximum acceptable weight of lift (MAWL), maximum comfortable weight of lift (MCWL), and maximum safe weight of lift (MSWL). Results demonstrated significant lifting instruction effects on the investigated dependent variables, including: selected load weight, selected load weight estimation, perceived physical effort, and perceived comfort and safety ratings associated with the selected load weights. Perceived acceptability of selected load weight was the only variable upon which lifting instructions did not have a significant effect. The results showed that the MAWL instruction led to selected loads that were significantly heavier than the loads selected under MSWL instructions. Also, the level of perceived physical effort under the MAWL condition was significantly higher than those obtained under the MSWL and MCWL conditions. Results from this study are consistent with previous research findings that psychophysical selection of lifting loads is very sensitive to the instructions provided to the subjects. It also is suggested that the application of the classical psychophysical approach to setting limits for manual materials handling tasks should be carefully reappraised.
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