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iterature reports many epidemiologic investigations
carried out to establish a link between exposure to upper
body vibrations and spine disorders. They show that
there is an association between the professional expo-
sure to vertical vibrations transmitted to the upper body
and an increased risk of adverse health effect [1-5]. Long
term Whole Body Vibrations (WBV) can generate adverse
health hazards for the lumbar spine, especially at the three
lower vertebrae (L3-L5). Several bibliographical reviews
have indeed been published over the past 15 years which
show a higher occurrence of low back disorders among
populations exposed to dynamic loading, such as heavy
equipment drivers, tractors, bus, metro, industrial equip-
ments, than with the general population [6-10]. Available
epidemiologic data is however not generally sufficiently
powerful to establish a dose-effect relationship between
exposure to whole-body vibrations and the risk of lumbar
disorders. In fact, experimental studies have shown that
dynamic loading induces dynamic stresses, principally
compressive, in the spine, that can produce microfractures
in the endplates and vertebral body [11-15]. The magni-
tude and distribution of loads on structural components
of the lumbar spine vary considerably based upon numer-
ous factors, and these will influence the structures and/or
patterns of failure observed. Among the factors influenc-
ing load magnitude and distribution are the posture [16],
the amount and distribution of the bone mineral content,
the size of the vertebral bodies and discs [13, 17], the
degree of the disc degeneration and the magnitude of the
compressive and shear forces imposed upon the spine.
Predicting the adverse health effects
to long term whole-body vibration exposure
Prédire les effets à long terme sur la santé dus
à l’exposition de l’ensemble du corps aux vibrations
Houcine Ayari, Marc Thomas, Sylvie Doré
École de technologie supérieure
1100, rue Notre-Dame
Ouest Montréal (Québec) H3C 1K3
Canada
E-mail : marc.thomas@etsmtl.ca
Rheda Taiar, Jean-Paul Dron
Université de Reims Champagne Ardenne
UFR STAPS
Laboratoire d’analyse des contraintes mécaniques
Moulin de la Housse
BP 1039
51687 Reims CEDEX 2
France
Tél. : 03 26 91 38 90
E-mail : rheda.taiar@univ-reims.fr
Résumé
L’objectif de cette étude est d’évaluer les risques de maux de dos encourus par des
chauffeurs suite à la fatigue mécanique des vertèbres lombaires générée par une
exposition à long terme à des vibrations du corps entier (WBV). Afin de se donner
de la souplesse dans la modélisation d’individus de différentes corpulences et de
caractéristiques physiques différentes, un modèle paramétrique par éléments finis
de rachis lombaire a été développé dans le but d’évaluer les contraintes dynamiques,
principalement pour les vertèbres L4-L5, suite à des excitations aléatoires.
Une estimation de la fatigue mécanique des vertèbres lombaires en a découlé, en
supposant que l’excitation aléatoire agissait principalement sur le premier mode de
compression. Les résultats ont montré que le risque de dommage augmente avec l’âge
en raison de la perte de propriétés mécaniques (module d’Young, densité osseuse,
contrainte ultime et amortissement des disques intervertébraux). En conséquence,
l’amplitude de l’excitation, telle que celle mesurée au niveau du siège du chauffeur,
doit être limitée en tenant compte du vieillissement des chauffeurs. Les résultats
ont révélé que l’accélération de l’excitation appliquée au siège doit être limitée à des
niveaux inférieurs à 2,3 m/s
2
, afin d’éviter tout risque, indépendamment de l’âge
du conducteur et de sa morphologie. Ce niveau a été considéré comme une limite
d’endurance du comportement en fatigue.
Abstract
The objective of this study is to describe a method in order to evaluate the long term
exposure limits to continuous whole–body vibration (WBV) before the occurrence of fatigue
failure, especially in the case of harmonic and random excitations. A parametric finite
elements model of lumbar rachis has been generated in the aim to compute the dynamic
stresses and estimate the mechanical fatigue under dynamic excitations. The assessment
of WBV is based on the quantitative relationships between accelerations (as measured
at the seat) and the dynamic stresses predicted at the L4-L5. A new model of fatigue
behaviour has been developed in order to estimate the risk of adverse health effects arising
frommechanical vibrations. As expected, it is shown that the injury risk increases with the
age due to the loss of mechanical properties (Young modulus, bone density, ultimate stress
and damping of the intervertebral disc). Consequently, the excitation amplitude must be
limited to lower levels when the age increases. The results have revealed that the excitation
acceleration applied to the seat must be limited to levels lower than 2.3 m/s
2
in order
to avoid any risk independently of the driver’s age and morphology. This level has been
considered as an endurance limit of the fatigue behaviour.
L