The Psychophysical Approach in Manual Lifting---A Verification Study

An experiment was conducted to verify the psychophysical methodology used for determining lifting capabilities of workers. After estimating during a 25-min period what they could lift for 8 h, males lifted for 8 h. The amount lifted was only 65% of the estimated value. Females, on the other hand, lifted 84% of the estimated weight. When the lifting duration increased from 8 h to 12 h, males lifted only 70% and females lifted 77% of the estimated weights. The metabolic energy expenditure rate of the subjects also decreased significantly with time as the loads were reduced. Heart rates remained relatively constant at about 100 beats/min, even though energy expenditure rates decreased over the 12-h period. This could indicate that the subjects were sensitive to their general state of physiological strain in such work and adjusted the loads and corresponding energy expenditure rates to maintain a relatively constant circulatory burden.