Psychophysical acceptability and perception of load heaviness by females.

The objective of the study was to evaluate subjective perceptions of load heaviness, and relate these perceptions to the maximal acceptable weights of lift. Ten female college students experienced in manual lifting participated in the study. In the first experiment, subjects were asked to select one of the seven linguistic values of load heaviness (very light, light, less-than-medium, medium, more-than-medium, heavy, and very heavy), which would best describe the lifted loads. Seven boxes, ranging in weight between 2.3 kg and 22.7 kg, were used for that purpose. In the second experiment, subjects were asked to fill empty boxes to the level they felt would best reflect a given load heaviness category. In the third experiment, the psychophysical methodology was used to determine the maximal acceptable weight of lift for an 8-hour day. The results showed that 50% of the subjects considered a 20.4 kg box (45 lbs) as very heavy, while another 50% believed that such a load was heavy. The average load selected as maximal acceptable weight of lift (MAWL) for an 8-hour day was 16.4 kg (standard deviation (SD) = 5.3 kg). When asked to determine the weights that would best describe a given category of load heaviness, the subjects selected 22.5 kg (SD = 3.7 kg) and 18.4 kg (SD = 2.7 kg) for very heavy and heavy categories, respectively. Further analysis revealed that only 30% of the subjects selected MAWL values that were larger than the pre-weighted boxes independently judged by them as very heavy or heavy categories. Also, 10% and 30% of the subjects selected MAWL values that were larger than the weights chosen during the self-classification procedure as representative of heavy or very heavy categories of load heaviness, respectively. It was shown that the loads selected as the maximum acceptable weights for an 8 h shift were independently judged by the female subjects as being in the more-than-moderate or heavy weight categories. Comparison of the results for females and males led to a conclusion that female subjects were more realistic, with respect to subjective perception of load heaviness, in selecting the MAWL values than were male subjects.