With some snow finally falling on the East coast, and tons of it already blanketing the Rockies and the West, many skiers are headed to the slopes with big fat skis to help them zip through fresh snow. But a Montana researcher believes that wide or "fat" skis may be causing unexpected knee injuries, especially when they're used on groomed trails.
The fat ski phenomena started a few years ago when ski companies designed a wider platform to help skiers stay above soft snow and deep powder. These "freeride" or "backcountry" skis between 100 to 115 millimeters (4.5 inches) wide, instead of a normal width of 80 to 90 millimeters. (3 to 3.5 inches). While that extra inch may not seem like much, it creates greater torquing force on a skiers' knee, according to John Seifert, professor of sports physiology at Montana State University.
"What we are finding is not real good unless you have a substantial change in ski technique," Seifert said. "Where we start to see increased problems, that happens around 85 to 90 mm underfoot. From there on up, that where we see increased torques and stress. The other aspect is the snow depth. Are you skiing on groomer, is it inch or two, foot or two of snow?"
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Seifert has used devices mounted on skiers' knees to measure the amount of force applied by skiers in several studies. His results show that skiers are forced to apply much greater rotational torque to turn a wider ski on groomed terrain with less than six inches of soft snow.
"What we see with a fat skis they are much faster from edge to edge change," Seifert said. With fat skis "they ski a straighter line. They tend to ski more parallel with the fall line, narrow carving ski. That difference can be about 5 to 10 percent faster with a fat ski. As a result, it takes a lot more muscle effort to get that fat ski on edge and to make the turn."
The popularity of fat skis has helped keep the industry afloat. Sales of snowboards have declined, while sales are up with fat skis and "freestyle" skis -- skis with rounded tips and tails to allow skiers to ski backwards in so-called "terrain parks" mimicking skateboard moves.
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Fat ski sales soared 50 percent in units to 22,052 pairs sold through December 2014, according to Snowsport Industries America, the ski industry trade group, including more fat skis in the icier, less powdery areas in the East and mid-Atlantic region.
Seifert says he is working with colleagues in Europe to further study the forces at work with fat skis, but doesn't have the funding to actually collect data on whether people are getting injured more. He says that anecdotally, he is receiving reports of greater knee injuries, however his attempts to talk to ski manufacturers about the issue have been met with a lack of interest.
Some ski bloggers have coined the term "fat ski syndrome" to describe greater muscle soreness when riding fat skis on groomed snow.
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In the Rocky Mountains, at least one doctor says he's definitely seeing more torn knee ligament injuries as a result of the fat skis.
"On powder days, we don't see any injuries," said Robert F. LaPrade, chief medical officer at the Steadman Philippon Research Institute in Vail, Colo. "It's usually four or five days without snow when it gets icier. I don't see people changing over [to skinnier skis]. Most people are skiing with powder type skies. Once the snow gets packed down, then we see torn ACLs. [anterior cruciate ligament]."
LaPrade, an orthopedic surgeon, says fat skis have become extremely popular at Vail.
"I would say more than 75 percent of people have them," LaPrade said.
In order to prevent knee injuries on fat skis, Montana State's Seifert recommends switching to a narrower ski on groomed terrain, and keeping the fat ski for true powder days of more than six inches.
LaPrade says keeping yourself physically fit will also help with overall injury prevention.