Adverse health effects to long term whole-body vibration exposure

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. The human exposure to Whole Body Vibration could cause discomfort, damage and adverse health effects, depending on the amplitude, frequency, duration of exposure, body type, density of bone, body weight and posture, etc. Literature refers to many causes that can produce problems related to low back pain. Many studies mention that these problems are found among a population exposed to long-term vibration loads, such as in transportation (tractors, trucks, buses, subways, other vehicles, etc.). Two assumptions may cause low back pain due to vibration exposure: the assumption that low back pain is due to soft tissue injuries (disc, muscle) or the assumption that they are due to bone damage. Most experimental studies have shown that under dynamic compressive loadings, the damage most often occurs in the vertebral body. Indeed, exposure to mechanical vibration excites the lumbar spine in a simple compression mode thus, such a loading can minimize the damage to discs since different mechanical models of intervertebral discs concluded that the disc herniation occurs mainly as a result of torsion or bending efforts coupled with the inclined lateral efforts. The generated dynamic stresses can be at the origin of accumulation of microscopic cracks in the bone (leading to fatigue damage of the bones) and this in despite of the potential for bone remodelling.With the hypothesis that low back pain among drivers comes from bone damage, the research was conducted in order to determine the long term limits of exposure to vibrations. Two models have been developed, a statistical analysis model and numerical simulations using a parametric finite clements model to study the effects of vibration on the lumbar vertebrae of drivers.