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

Abstract

A laboratory study was conducted to evaluate the effects of lifting frequency and technique on maximum acceptable work loads using psychophysical measurement technique, and 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 min. Four levels of lifting frequency (3, 6, 9 and 12 lifts/min) and 3 different lifting techniques (free style, stooped back and straight-back, bent-knee) were employed. O2 consumption rates were measured at maximum acceptable work loads and were reduced to STPD [standard temperature, pressure and dry air]. 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 6 of the 12 combinations of lifting frequency and technique. Use of the physiological fatigue criteria results in more liberal standards of work load at low work paces, especially for the stooped back and the free style lifting techniques.