In this paper, A new biodynamical model was developed with the objective of analyzing the dynamic responses of the human back during the exertion of symmetric lifting activities. More emphasis was placed on the study of the lumbosacral disc located between the fifth lumbar and first sacral vertebrae (L5/S1). The present model accounts for the sliding components of velocity and acceleration as well as the Coriolis acceleration in the kinematical equations of the human back. The inclusion of those terms has enabled a more accurate computation of the generated sliding effect of the flexible disc as well as the change in its height and width which normally occurs during the gross body rotation of the back. This has turned to have a significant effect on the resulting compressive force applied at the L5/S1 region. A computer model was developed in this study to automate the biodynamical simulation processes for workers of different genders and for a vast range of body postures. Results indicated that the inclusion of the sliding components of velocity and acceleration do actually have a significant effect on the whole range of lifting activities in which an angular velocity exceeding 24 degree/sec is employed. Results obtained in this paper were compared with the experimental and computational (simulated) results of recent relevant publications. The comparison shows that there are good agreements between the results for angular velocities exceeding 24 degree/second, which is known as the normal range of operation in lifting activities. Results obtained in this paper were in good agreement with NIOSH action and maximum limits which make it reliable for use as a guideline to help workers in industry to avoid hostile lifting activities and bring to attention an early warning to avoid engaging industrial labors with postures leading to severe back pain problems.

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