Snowmobiler's Back

Snowmobilers have been accused of everything from terrorizing wildlife to vandalizing hunters' cabins. From Alaska to Maine, the nation's 19 snowbelt states are passing or planning new laws to regulate the noisy off-road machines. But even if all drivers are eventually licensed, they seem likely to cause more damage--at least to themselves. Last year 84 U.S. snowmobilers died in accidents ranging from train collisions to falling through thin ice. Reasonably prudent drivers, in fact, can be hurt by merely emulating the ads and "flying" their new toys well above ground.

The experience is exhilarating, but the landings can be rough. The impacts often cause "snowmobiler's back," a compression fracture in which several vertebrae are rammed painfully together. Last year hurt spines accounted for roughly 13% of the nation's 306 reported snowmobile injuries, and investigators at the University of Michigan's Highway Safety Research Institute have recently found out why. According to Drs. Verne Roberts and Robert Hubbard, soaring snowmobilers are subjected to even greater G forces than pilots being ejected from disabled jets.

Lifetime Pain. The Michigan team based its findings on tests with a special sled, ten typical snowmobile seats and a 225-lb. dummy fitted with stress-sensing instruments. When the sled with its seated dummy was dropped 4 ft. onto a concrete platform--the equivalent of a jump in a fast-moving snowmobile--the jolts produced downward forces of 20 to 34 times the force of gravity, enough to make the body weigh anything from 4,500 lbs. to 7,650 lbs. at the instant of impact. Aircraft ejection seats, which are activated by an explosive charge, subject the body to about 13 Gs, while other tests have shown that 20 Gs is enough to produce injury even without impact.

Compression fractures are often accompanied by ruptured spinal discs and torn muscles. Victims may spend as long as five months in a torso cast or in traction. Some face a lifetime of continuing pain or disability.

Noting that the best of the tested seats absorbed only 15% of the energy of impact, the Michigan researchers suggested that snowmobile makers could reduce injury by significantly stiffening the materials used in their machines' cushions. To discourage reckless driving, some makers have already decided to downplay jumping in new advertising. But the most important step toward preventing injuries must be taken by the nation's some 1,600,000 snowmobilers, who can save spines by avoiding acrobatics.

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