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A Biomechanical Assessment Of Axial Twisting Exertions

Kevin P. Granata, William S. Marras

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Axial twisting of the torso has been identified as a significant risk factor for occupationally related low-back disorders. The purpose of this investigation was to examine the influence of dynamic twisting parameters upon spinal load. Measured trunk moments and muscle activities were employed in a biomechanical model to determine loads on the lumbar spine. Spinal loads were examined as a function of dynamic torsional exertions under various conditions of force, velocity, position, and direction. Results demonstrate significant flexion-extension and lateral moments were generated during the twisting exertions. Muscle coactivity was significantly greater than equivalent levels measured during sagittal lifting exertions. Relative spinal compression during dynamic twisting exertions was twice that of static exertions. Spine loading also varied as a function of whether the trunk was twisted to the left or right, and the direction of applied torsion, i.e. clockwise versus counter-clockwise. The results may help explain, biomechanically, why epidemiological findings have repeatedly identified twisting as a risk factor for low-back disorder