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Abstract
The presented work aims at analyzing the reaction of the human body at themain joints of the skeleton during some biomechanical activities such as lifting.and pushing of loads. Emphasis in this research was placed on the study of thelower region of the back located between the fifth lumbar vertebra and the firstsacral vertebra (L5/S1), known as the lumbosacral disc region. Two modelswere developed in this work. The first is a static biomechanical model consistingof seven rigid body segments which were used to compute the forces generatedin the back during symmetrical (sagittal) and asymmetrical lifting activities. Thesecond model deals with the dynamic forces generated in the back during thesymmetrical lifting activities. Two additional rigid body segments were added inthe second dynamic model to enable accounting for relative motion arising fromconsidering the relative velocity and acceleration as well as the Coriolisacceleration in the kinematics equation of the human back. The inclusion ofthese terms has enabled a more accurate computation of the forces generated atathe L5/S1 region. This has also enabled the computation of the generated slidingeffect of the flexible disc as well as the change in its height and width which anormally occurs during the gross body rotation of the back. It is worthmentioning that the literature survey did not reveal that the above kinematicsparameters were used in previous research works. The results of the presentwork are compared with the experimental and computational (simulated) resultsof recent relevant publications. The comparison shows that there are fairaagreements between the results for angular velocities less than 24degree/second. The agreements between the results are even better for angularvelocities exceeding 24 degree/second, which is known as the normal range ofoperation in lifting activities. The results are also compared with NIOSH actionlimit (3400 N) and maximum limit (6400 N) and can therefore be used asguidelines to help workers in industry to avoid postures leading to back painproblems.