Abstract
Objectives: Epidemiological studies reveal that long-lasting exposure to whole-body vibrations, especially the vibrations of earth-moving machinery, can induce degenerative changes in the lumbar spine. The purpose of this study was to assess the mechanical overexertion risk on the basis of predicted spine forces. Methods: The forces were simulated by means of a biomechanical model, where 16 rigid bodies represent the trunk (5 bodies), the neck (4), the head (1), and the two arms (6) and one additional body imitates the vibrating seat. The seat accelerations were computed on the basis of the power spectral density given in ISO 7096. Results: The simulations resulted in peak values of the compressive spinal force reaching from minimal −161 N to maximal −1020 N under vibration stress whereas the force was −530 N during still erect sitting. Further a measure for the risk of mechanical overexertion was computed by means of the spine forces, the recommended compressive strength and the endurance strength of the lumbar spine. The age-related compressive strength values were taken from the literature. The endurance strength was set to 20 % of this strength. Conclusions: Regarding this measure it could be shown that the overexertion risk increases with the age of the operators exposed to vibrations similar to those of tractor-scrapers, wheel-tractors, or -loaders. Suggestions are provided concerning the attenuation of vibration stress by the seats.