PSYCHOPHYSICALLY DETERMINED ASYMMETRICAL LIFTING CAPACITY OF CHINESE MALES OVER AN 8h WORK SHIFT

ABSTRACT A laboratory study was conducted to investigate the effects of asymmetrical lifting on the psychophysically determined maximum acceptable lift weight (MAWL) and resulting heart rates and ratings of perceived exertion (RPE). Eight Chinese 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 a 76 cm high shelf at a rate of one-time maximum, 1 and 4 lifts/min using a free-style lifting technique. The results showed that: (1) The maximum acceptable weights were significantly lower for asymmetrical lifting than for symmetrical lifting in the sagittal plane. The maximum acceptable lift weight decreased with an increase in the angle of asymmetry, however, the heart rate and ratings of perceived exertion remained unchanged; (2) The lifting frequency had no significant effect on the percentage decrease in maximum acceptable lift weight during asymmetric lifting, using the symmetric lifting in the sagittal plane as the base line. Correction factors of 6, 11, and 16% for maximum acceptable lift weights at 30°, 60° and 90° in asymmetrical lifting, respectively, are recommended. The values are lower than those of the asymmetry multiplier of the 1991 NIOSH equation.(3) Both heart rate and RPE increased with an increase in lifting frequency though maximum acceptable lift weights decreased. The maximum acceptable weights decreased markedly by nearly 40% and 49% from one-time maximum to one lifts/min and four lifts/min, respectively. The heart rates increased by nearly 19% from one lifts/min (94.3 beats/min) to four lifts/min (112.5 beats/min). The most stressed body part was the lower back.

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