Application of finite-element models to predict forces acting on the lumbar spine during whole-body vibration

Objective. To predict forces acting on the spine during whole-body vibration for a variety of boundary conditions body mass, height and posture. Design. Representative anthropometric data and models for an upright, relaxed and bent forward sitting posture were used to derive model families with 30 variants of a finite-element model. Background. A given exposure to whole-body vibration can cause a variable health risk depending on the concomitant conditions. The latter could contribute to the considerable uncertainty of the current evaluation of whole-body vibration. Methods. Plane symmetric linear finite-element models were used for the prediction of static and dynamic compression and shear forces acting on the lumbar discs during whole-body vibration. Transfer functions from seat acceleration to forces were determined. Results. A bent forward posture augments essentially the compressive and shear stress, predicted for erect and relaxed sitting postures. The normal variation of body mass and height causes a considerable variation of static internal shear stress, but a minor variation of compressive pressure. The dynamic internal stress varies nearly proportionally to the body mass. The transfer functions from seat acceleration to compressive force depend significantly on the posture. Conclusions. The variability of the spinal loads for a given whole-body vibration and associated with a normal range of several biological factors suggests a ratio between the minimum and maximum internal loads of about 1:2.