Investigation of the Effect of Whole-Body Vibration on the Human Body by Spine Modelling 2005-01-2715

Low back pain presents a common problem in occupational health, where exposure to vibration in vehicles is recognised as an important risk factor. It is commonly accepted that long-term exposure to whole-body vibrations can induce degenerative changes in the lumbar spine, but it is not understood what injury mechanisms are responsible for the problems involved. The standard approach is to model and to measure spine movement in response to low frequency vibrations (in the range of 0-20 Hz), in order to make a realistic prediction of vibration transmission through the human body, and of consequent pressure/tension between spine segments. This information, together with data on muscle behaviour, should produce an improved understanding of the spinal movements caused by vibration, and provide objective means for comfort and health evaluation of specific vibration frequencies and body postures.

Therefore a two-dimensional active biomechanical model is presented which allows the determination of these unknown internal forces between spine segments. This model consists of the sacrum, the lumbar and thoracic vertebrae, a neck and a head. All these parts are modelled as rigid bodies, connected by non-linear stiffnesses. Geometry, inertial properties as well as the musculature of the model are determined according to human anatomy.

Furthermore experiments are executed to determine seat-to-head transmissibilities, while the subjects were sitting in three different postures (erect, normal and slouched). These transmissibilities are used to evaluate the model. Finally the intradiscal compressive forces are used as an estimate for the intradiscal pressure, which is a parameter that gives an idea about the severity of the vibrations and its possibility to give rise to damage of the intervertebral discs.