Maximum acceptable weights and maximum voluntary isometric strengths for asymmetric lifting

A laboratory study was conducted to determine the effects of asymmetric lifting on psychophysically determined maximum acceptable weights and maximum voluntary isometric strengths. Thirteen male college students lifted three different boxes in the sagittal plane and at three different angles of asymmetry (30,60 and 90°) from floor to an 81-cm high table using a free-style lifting technique. For each lifting task, the maximum voluntary isometric strength was measured at the origin of lift. The maximum acceptable weights and the static strengths for asymmetric lifting were significantly lower than those for symmetric lifting in the sagittal plane for three box sizes (P<0·01). The decrease in maximum acceptable weight and static strength from the sagittal plane values increased with an increase in the angle of asymmetry (P < 0·01). Box size had no significant effect (P≥ 0·05) on the percentage decrease in maximum acceptable weight or voluntary isometric strength from the sagittal plane values. Correction factors of 7,15 and 22% for maximum acceptable weights and 12, 21 and 31% for static strength at 30, 60 and 90% of asymmetric lifting are recommended. Lastly, in the absence of epidemiological data, a comparison of maximum acceptable weight and static strength in the sagittal plane with the NIOSH guidelines for action and maximum permissible limits indicates that the guidelines may be conservative.