Further studies of psychophysically determined maximum acceptable weights and forces

The effects of lifting boxes without handles, pulling long distances, carrying different size boxes, combining three handling tasks, and lifting with extended horizontal reach were studied using a psychophysical methodology. Six male industrial workers performed 42 variations of lifting, lowering, pushing, pulling, and carrying tasks. Lifting boxes without handles produced consistent decreases (median, 16%) in maximum acceptable weights when compared with lifting boxes with handles. Lifting with extended horizontal reach (approximately 48 cm) produced consistent decreases (median, 48%) in maximum acceptable weights when compared with lifting close to the body (approximately 17 cm). No significant heart rate or oxygen consumption differences occurred in either of these variables. No significant differences in maximum acceptable weight of carry were observed among box sizes; however, the maximum acceptable force of pulling was lower for longer (15.2 m) pulling tasks. The maximum acceptable weight for combination tasks was similar to that of the limiting component.