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Shake, Rattle and Roll

Rally car drivers at high risk for extreme vibration injuries

FRIDAY, Sept. 28, 2001 (HealthDayNews) -- The teeth-rattling shakes inside a speeding professional rally car can trigger muscle and bone problems, including back and neck pain, hand and wrist problems and even problems with fine motor movements of the fingers, says new research.

A study in the October issue of the British Journal of Sports Medicine, says the findings apply not only to rally-car drivers but to people whose jobs involve vibration exposure, including industrial truck drivers, people who use heavy equipment in the farming, forestry or quarrying industries and people who regularly use vibrating hand tools, like shipyard workers.

Lead author Neil Mansfield, who normally studies industrial exposures to vibration and impacts, was looking for people who are exposed to extreme vibration over relatively short periods of time, and rally drivers turned out to be the ideal subjects. Mansfield is personally familiar with the severity of the vibration, as he's navigated a rally car before.

"If you can imagine, when you get out of the car, every joint will ache," he says. "You may also find that some of your muscles ache, as well. You don't realize that you've been clenching your teeth and [sustaining] very high muscle tension to brace yourself against any of the impacts."

Mansfield and his team surveyed 118 rally participants from the 2000 season, looking for those who had raced on 10 days or more that year. The races are on closed roads with no speed restrictions in high performance vehicles. Roughly 10 percent of the drivers in the study were women, which is fairly representative of the sport, says Mansfield.

Of the 90 people who met the criteria, 82 said they'd had discomfort in at least one body area after competing. The most common discomfort was in the lower back (70 percent), followed by neck pain (54 percent) shoulder pain (47 percent) and mid-back pain (36 percent).

One advantage of studying the drivers and their navigators is that they are a matched pair of subjects with similar exposures. Still, the researchers did find subtle differences in the symptoms of drivers and co-drivers.

Compared to 46 percent of drivers, 62 percent of navigators reported neck pain. Co-drivers also were more likely to report knee and elbow pain.

Ten percent of drivers reported wrist pain, compared to 2 percent of navigators, while 15 percent of drivers and 4 percent of co-drivers described hand pain. Almost one-third of drivers reported tingling, numbness or whitening of their hands.

"For the drivers, we showed that they did have more problems at the hand and at the wrist, much more than the co-drivers did," says Mansfield. "The only difference is that the drivers are holding the steering wheel, so the forces that are coming from the steering wheel … are causing this."

"The hand-arm vibration can cause problems like carpal tunnel syndrome," and hand-arm vibration syndrome, which can include a problem called vibration white finger, says Mansfield.

"This is usually found in people who operate vibrating tools like road drills [jackhammers]," he says. "They find that they lose circulation in their fingers, and their fingers all turn white when it gets cold. The blood supply will be cut off from the fingers, and this is because there's been nerve damage in the hand." However, the vibration in the cars did not appear serious enough to cause this incurable problem.

Mansfield says design adjustments to reduce vibration in rally cars are unlikely because they would affect speed or performance. But he says participants can wear neck padding systems and choose lighter helmets to reduce stress on the neck.

Mansfield says, ironically, rally participants probably will benefit the least from the findings. "They will expose themselves to extreme environments until they can't bear it any longer," he says.

He says the study more likely will help people exposed to severe vibration on the job by helping researchers determine levels of exposure that cause permanent nerve and circulatory damage and chronic pain.

Paul-Émile Boileau, a researcher specializing in the human response to vibration and shock, says setting guidelines that limit exposure is complicated because it's still not clear how much vibration is dangerous. "At this stage, nobody has been able to actually define a dose-response relationship," he says.

However, Boileau says several European countries are in the process of establishing occupational vibration exposure limits. "There are some countries that actually recognize low-back pain originating from vibration exposure as an occupational disease," he says. Belgium, the Netherlands, Germany and most recently, France, now provide compensation for the problem, and British researchers are studying vibration exposures in other motor sports, he says.

What To Do

Check the Web site for the South Florida Spine Clinic for a primer on spine anatomy. (You will need Macromedia Shockwave Player to read this page).

Or look through this National Institute for Occupational Safety and Health publication on vibration syndrome.

Or, if you just want to dream, here's the Grand Prix de Monaco.

SOURCES: Interviews with Neil J. Mansfield, Ph.D., B. Eng., lecturer, Department of Human Sciences, Loughborough University, Loughborough, U.K., and Paul-Émile Boileau, Ph.D., researcher, Research Institute of Occupational Safety and Health, Montreal, Quebec, October 2001 British Journal of Sports Medicine
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