The effect of load and posture on load estimations during a simulated lifting task in female workers

The objectives of this study were: (1) to determine the effects of posture and load on relative load estimates (RLE) and absolute load estimates (ALE) of a one hand-lifting task within female checkout operators; (2) to quantify the magnitude of the over- and underestimations of the absolute load estimates in three different postures; and (3) to compare the RLE and ALE responses with respect to correct, under- and overestimations of the load. Eighteen experienced, healthy female checkout operators lifted standardized containers of three different weights (28.9, 33.4, 37.8 N) in three different postures (normal, maximum, extreme) for two trials. For each condition, the weight of the test container was estimated in relative and absolute terms. A binary logistic regression for the RLE and a balanced ANOVA with repeated measures was used to test the main effects and interactions for the ALE. An alpha = 0.05 was used for all tests of the RLE and ALE. These results showed a statistically significant interaction for posture and load, indicating that different combinations of load and posture affected load estimation differently. It was observed that overestimation of the load occurred in the maximum and extreme postures while handling the heavier loads, whereas underestimation occurred in the normal posture lifting the lightest load. In general, individuals were better able to correctly identify the relative effect of the load than to estimate the weight of the load in absolute terms. Relevance to industry In many cases the establishment of load handling limits by physicians and rehabilitation specialists during rehabilitation and return to work programs are based upon the workers' self-report of loads handled in the workplace. However, the literature indicates that load estimates and ratings of perceived effort are non-linear. The results of this study have shown the independent and interactive effects of loads and postures during a simple load-handling task. (C) 2003 Elsevier Science B.V. All rights reserved.