Effects of lifting frequency and technique on physical fatigue with special reference to psychophysical methodology and metabolic rate.

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.