A MATHEMATICAL LIFTING MODEL OF THE LUMBAR SPINE

The objective of this study was to develop a comprehensive mathematica l lifting model which takes into account both task and personal factor s. The outcome measure of this model was compared to that of the 1981 and 1991 NIOSH lifting equations as well as the model reported by Drur y and Pfeil (Int J Prod Res 13:137, 1975). The model was developed in two stages. In the first stage, the complete model was derived from th e psychophysical data. In the second stage, the discounting factors of the various parameters included in the model were tested and adjusted using the physiological and biomechanical data, The rationale for bui lding the model in two stages was based upon the hypothesis proposed a nd tested by Karwowski (Proc Ergon Soc Conf 95, 1983), which, combinin g the acceptability of physiological and biomechanical stresses, shoul d lead to an overall measure of lifting task acceptability-namely, the acceptability of psychophysical stress. The following input parameter s were incorporated into the model: (a) horizontal distance in the sag ittal plane, (b) vertical distance between the origin of lift and the floor. (c) vertical travel distance, (d) lifting frequency, (e) task d uration, (f) twisting angle, (g) coupling, (h) heat stress, (i) gender , (j) age, (k) body weight, and (1) percentage of worker population. T he lifting capacity values predicted from the present study are consis tently lower than the values generated from prior research. This can l argely be explained by the incorporation of new biomechanical and phys iological guidelines for lifting tasks.