Maximum acceptable weights, heart rates and RPEs for one hour's repetitive asymmetric lifting

A laboratory study was conducted to determine the effects of repetitive asymmetric lifting on psychophysically determined maximum acceptable weights and resulting heart rates and ratings of perceived exertion (RPE). Eight male college students lifted a box in the sagittal plane and at three different angles of asymmetry (30, 60 and 90°) from the floor to an 81 cm high table and from an 81 cm high table to a 152 cm high table at a rate of 3,6 and 9 lifts min−1 for a period of one hour. For each lifting task, static strength was measured at the origin of lift. The maximum acceptable weights and static strengths were significantly lower and heart rates and RPEs were significantly higher for asymmetric lifting than those for symmetric lifting in the sagittal plane (p0·05) on the percentage decrease in maximim acceptable weight from the sagittal plane values. Correction factors of 9,14 and 21% for maximum acceptable weights and 17,31 and 42% for static strength at 30,60 and 90° of asymmetric lifting, respectively, are recommended. Maximum acceptable weights were 6 to 9% greater and heart rates were significantly lower (p<0·01) for a 0·81 m to 152 m lift than those for the floor to 0·81 m lift. Both heart rate and RPE increased with an increase in lifting frequency (p<0·0l) though maximum acceptable weights decreased (p<0·01). Effects of asymmetric lifting, lifting frequency and lifting height on psychophysical and physiological responses are discussed.