Simulated dynamic lifting strength models for manual lifting
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An experiment was designed and conducted for the development of the mathematical models for prediction of the weight lifting capacity of individuals for lifting a box and a bag from floor to shoulder height and knuckle to shoulder height at frequencies of 2 and 6 lifts per minute. The dependent variable was the maximum acceptable amount of lift and the independent variables were task- and operator-related. The operator variables included the dynamic strength of the subjects in a simulated lifting position, static strengths, height, weight, endurance, and the physical work capacity. The task variables were container type, lift type, and frequency of the lift. A total of nine males participated in this experiment as the subjects. During a period of one month (June, 1982) the required anthropometric', strengths', and lifting data were collected. The SAS procedures were used to develop and test the models. The data from six subjects were used to develop a total of 18 models (nine dynamic and nine static). The data from the three remaining subjects along with the data from the previous studies (available in the literature) were used to test and validate the models. I t was concluded that both the dynamic models and the static models developed in this study can predict the maximum acceptable amount of lift with a reasonable degree of accuracy. However, a comparison of the static and dynamic models revealed that the use of the dynamic models reduced the average absolute error between the actual and predicted load up to 44 percent. A simple dynamic model involving only one operator strength measure was thus found to be a good predictor of lifting capacity and was superior to the static models.