Prediction of the maximum acceptable weight of symmetrical and asymmetrical lift using direct estimation method

Abstract

The objective of this research was to study the effectiveness and accuracy of using the direct estimation method to determine a worker's lifting capacity or MAWOL of symmetrical and asymmetrical lifting tasks. Sixteen lifting tasks involving four different lifting angles and lifting frequencies were studied. The influence of these independent variables on MA WOL was analysed. In the first session of the study, ten male subjects performed sixteen lifting tasks to predict the MA WOL for each task condition using the psychophysical method. In the second session of the study, the MAWOL for sixteen task conditions were estimated using the direct estimation method. The results of this study indicate that direct estimation is an accurate method to establish MAWOL quickly for a series of lifting tasks. Analysis of the MAWOLs determined by two different methods indicated no significant difference between these two values. However, a significant difference was found between the direct estimated MAWOL and the psychophysicaly predicted MAWOL at the frequency of I lift/min with 30° or 60° asymmetry. This finding shows the limitation of the direct estimation method in developing MAWOL which indicates as the interval between lifts increases, subjects have difficulty in making accurate estimates of the stress of the specific task.

Keywords:

• Direct estimation
• Psychophysical methodology
• Symmetrical and asymmetrical lifting
• Task ratings