Utilization of Direct Estimation Method to Predict the Maximum Acceptable Weight of Symmetrical and Asymmetrical Lift

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. In the first part of the study, ten male subjects performed sixteen lifting tasks to predict the MAWOL 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 MAWOLs and the psychophysical predicted MAWOLs at the frequency of 1 lift/min with 30° or 60° asymmetry. This finding indicates as the interval between lifts increases, subjects have difficulty in making accurate estimates of the stress of the specific task, therefor, the direct estimation method should be used with caution.