Millions of European
workers are exposed to mechanical vibration transmitted to their hands from
powered tools or transmitted to their whole body from the seats of industrial
vehicles. Disorders of the upper limbs caused by hand-transmitted vibration
are among the most compensated industrial diseases in several European states
and exposure to whole-body vibration is associated with disorders of the spinal
The currently standardised methods of assessing the severity of vibration exposures are not based primarily on epidemiological evidence or on an understanding of the relevant mechanisms of injury. They are not sufficient to predict the risks of injury or define optimum means of preventing injury.
The principal objective of VIBRISKS was to improve understanding of the risks of injury from exposures to hand-transmitted vibration and whole-body vibration at work by means of multi-national epidemiological studies, supported by fundamental laboratory research and biodynamic modelling. Secondary objectives were:
studies of hand-transmitted vibration (HTV) and whole-body vibration (WBV) were
designed to be complimentary, since they involve many common tools and procedures.
For both HTV and WBV, the work was divided into three components:
In Italy and Sweden, baseline and follow-up longitudinal epidemiological studies were completed with groups of workers having different exposures to hand-transmitted vibration. A second follow-up survey was completed in Italy. The Italian survey provided evidence of dose-response relationships for sensorineural and vascular symptoms and a dose-effect relationship for cold-induced digital arterial hyper-responsiveness and impaired manual dexterity in HTV-exposed workers. The Swedish study group had only short vibration exposures, but significant associations were found between indices of peripheral vascular and sensory dysfunction and measures of daily and cumulative vibration dose. Vibration exposure and awkward neck postures were associated with neck pain among the workers.
Experimental and modelling studies of hand-transmitted vibration
Collaborative experimental studies on hand-transmitted vibration were carried out in Italy, Sweden, and the UK to improve understanding of the effects of vibration magnitude, frequency and duration on acute changes in both vascular function (finger blood flow and finger systolic blood pressure) and neurological function (vibration perception thresholds and thermotactile thresholds). The observed changes in vascular and sensorineural function during and following vibration exposure were not consistent with the 'energy-equivalent' time-dependency currently used to evaluate occupational exposures to hand-transmitted vibration. The vascular studies suggest that intermittent vibration is less hazardous than continuous vibration with the same 'energy'. Reductions in finger blood flow were not limited to the finger experiencing force and vibration. Both vibration magnitude and exposure duration influenced thermotactile thresholds.
Experimental studies in Italy and the UK suggested that recent exposure to force and moderate levels of hand-transmitted vibration will not greatly affect finger systolic blood pressure following cold provocation, as used to identify vibration-induced white finger. In Sweden, prior exposure to vibration on the day of a test was found to influence vibrotactile and thermotactile perception thresholds.
In the UK, studies of the
effects of age and gender on vascular function (finger systolic blood pressure
after cooling) and sensory function (thermotactile and vibrotactile thresholds)
provided normal values to assist the interpretation of clinical and epidemiological
studies of the hand-arm vibration syndrome.
In France, a 3-D biodynamic
model of a finger was elaborated to understand how vibration propagates in the
tissues and how to calculate internal mechanical properties, such as strain.
The studies also improved understanding of finite element calculations of visco-hyperelastic
In Italy, Sweden, the Netherlands and the UK, baseline and follow-up longitudinal epidemiological surveys were completed with groups of workers occupationally exposed to whole-body vibration. A further follow-up survey was completed in Italy and an intervention study in the Netherlands continues to investigate the effects of health surveillance and other intervention measures. Various physical and psychosocial factors were found to be associated with an increased risk of low back pain (LBP). The Italian and the Dutch results were consistent with increased risk of LBP in those with higher cumulative exposures to whole-body vibration. However, standardised measures of daily vibration exposure were poorly associated with LBP. Studies in Sweden and the UK did not find clear relationships between WBV and LBP.
The findings of the case-control
study in the UK suggest that, in the general population, WBV is not an important
cause of LBP that is severe enough to result in referral for MRI imaging of
the lumbar spine.
Experimental and modelling studies of whole-body vibration
In Germany, experiments and modelling of the spinal system led to a new method of predicting spinal stress from vibration in vehicles. A numerical model of the spinal system was extended to predict load on the spine from the forces caused by combinations of driver posture and whole-body vibration. When applied to the vibration measured in the epidemiological studies, the evaluations indicated an underestimation of health risks by the exposure limit value in the Physical Agents (Vibration) Directive.
Protocols were developed for the epidemiological studies of hand-transmitted and whole-body vibration. These defined measures of vibration dose, means of summarising exposures and their effects, and self-administered and clinically-administered questionnaires for the baseline and follow-up studies. The protocol for hand-transmitted vibration also defined tests for diagnosing the hand-arm vibration syndrome. The protocols are valuable guides for future research and should also assist clinical studies.
VIBRISKS also produced
health surveillance guidance that will help occupational health workers to minimise
risk, screen exposed individuals, and manage individuals with symptoms of vibration
The epidemiological and experimental studies of hand-transmitted vibration indicate that improvements are possible to the frequency weighting and the time-dependency currently used to predict the risks of vibration-induced disorders. The results confirm that finger systolic blood pressure after cold provocation is related to vibration exposure, and that both thermal thresholds and vibrotactile thresholds are indicators of sensorineural damage caused by hand-transmitted vibration.
The studies of whole-body vibration indicate that improvements are needed to the method of predicting risks to the low-back. Risks of injury to the low-back due to mechanical forces are complex and multi-factorial and cannot be predicted solely from measurements of vibration. Especially important are postural factors that have been shown to influence spinal forces and the risk of low back pain.
The findings have implications for the Physical Agents (Vibration) Directive of the EU and the development of new standards. However, the subject is very complex and there are many implications associated with any change to current procedures. Further research on hand-transmitted and whole-body vibration is required before specific changes can be confidently recommended.
VIBRISKS has contributed to the prevention and control of vibration-induced disorders by disseminating new methods, new findings, and experience from the project to occupational health professionals, standards committees (national, European, and International), and to employers and their workers.
The VIBRISKS Final Report and all 21 Annexes are publicly available to assist others undertaking relevant research. The VIBRISKS protocols for diagnosing vibration-induced injuries, and the VIBRISKS guidelines for the health surveillance of persons exposed to hand-transmitted vibration or whole-body vibration, are available for application by occupational health workers across Europe and worldwide.
Two international conferences and workshops were organised by the VIBRISKS project team to disseminate information from the project: (i) the 3rd International Conference on Whole-body Vibration Injuries in Nancy, France (7-9 June 2005) and (ii) the 2nd International Workshop on HTV Injuries in Gothenburg, Sweden (6-7 September 2006). The results are also presented in many papers already published or awaiting publication in scientific journals.
Institute of Occupational Medicine, University of Trieste, Italy
in association with
in association with
Department of Biomedical Engineering & Informatics, University Hospital of Northern Sweden
in association with