A laboratory study was conducted (1) to evaluate the effects of lifting frequency and technique on maximum acceptable work loads using psychophysical measurement technique, and (2) to compare the physiological fatigue criteria of 5 Kcal/min with the psychophysical fatigue criteria by measuring the metabolic rates at maximum acceptable work loads determined by subjective estimates of physical fatigue. Six male college students were required to lift from the floor to a 0.5 m height for 40 minutes. Four levels of lifting frequency (3, 6, 9 and 12 lifts/min) and three different lifting techniques (free sytle, stooped back and straight-back, bent-knee) were employed. Oxygen consumption rates were measured at maximum acceptable work loads (and were reduced to STPD). Statistical analysis showed that the maximum work loads acceptable to the workers were significantly affected by both lifting frequency and technique. Maximum acceptable work loads increased with an increase in lifting frequency. Both the subjective estimates of physical fatigue and the metabolic energy expenditure rate favored the free style lifting technique. The measured metabolic rates were in agreement with the physiological fatigue criteria of 5 Kcal/min only for six of the twelve combinations of lifting frequency and technique. Use of the physiological fatigue criteria will result in more liberal standards of work load at low work paces, especially for the stooped back and the free style lifting techniques.

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A laboratory study was conducted to evaluate the effects of handles, shape of the container, and dimensions of the container on maximum acceptable weight of lift using a psychophysical methodology. Ten male college students were required to lift six different boxes with handles, six without handles, and three different mailbags from the floor to a bench height (76 em), using a free-style lifting technique. The six boxes varied in length and width, and the three mailbags varied in diameter and length. Statistical analysis showed that the maximum acceptable weights for mailbags and boxes without handles were lower than those for boxes with handles. The maximum acceptable weight significantly increased with an increase in dimensions of the mailbag. Among all the container characteristics studied, handles were found to have the most profound effect on maximum acceptable weight. It is concluded that the recommendations for maximum acceptable weight of the load based on boxes with handles need to be adjusted when applied to boxes without handles or to some other types of containers.

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