Jim Graupner is on a quest for exhaustion.

When the 70-year-old retired history teacher from Lake Elmo began running in 2002, he quickly became "obsessed like you wouldn't believe" with the sport. He soon started running distance races, gradually building his endurance. Some years he's run more than 30 races, including marathons in Duluth, the Twin Cities and Boston.

But running outside in winter can be slippery, dangerous business. And he found running indoors sterile and often boring. In 2005, Graupner found an outlet to satiate his desire for physical exertion in winter — snowshoe racing.

"I do love that feeling of working myself to the point of exhaustion, and snowshoe racing can be grueling — it's very similar to running barefoot on a sandy beach," Graupner said. "But it's more than just the racing and the competition. I think running on the snow is just a wonderful thing to do. Winter is beautiful, and you just can't buy enough cold weather, if you ask me. You could say that running and now snowshoe racing have opened a whole new world to me."

Indeed it has. Racing has opened him to national acclaim. He's a national champion nine times over in different age categories. And Graupner is a top racer in his age group (age 70-74) this weekend at the national championships happening at Lowes Creek County Park in Eau Claire, Wis.

The location speaks to snowshoe racing's growing interest and talent in the Midwest, according to one of the sport's top officials.

"Snowshoe racing is growing across the United States, and we're adding new events every year," said Mark Elmore, sports director for the United States Snowshoe Association, the New York-based governing body in the United States. "It's an exciting time. The Midwest has turned into a hotbed of racing; Minnesota and Wisconsin have several qualifiers this year, which makes Eau Claire a great venue for the nationals."

About 350 of the best U.S. racers across gender, age group and distance will compete in Eau Claire. The races include the signature men's and women's 10K, as well as a half-marathon — a new event for 2015. There also are junior boys' and girls' races and a team relay.

Snowshoe racing is popular, Elmore and others say, because anyone of any age can do it. Other pluses: It demands minimal gear, is relatively inexpensive (most snowshoes designed for running cost $300 or less) and is a great calorie-burning workout. "If you can walk, you can snowshoe, and if you can run, you can snowshoe race," Elmore said. "People snowshoe race for many different reasons. Some want a winter activity, while others like to meet new people and expand their social circle. Everyone is different."

Kelly Mortenson, 43, owner of Run MN, a shoe store in Burnsville, and an avid marathoner, said snowshoe racing is a great cross-training activity that complements his year-around running. Mortenson has run 35 marathons and, during his heyday, logged as many as 140 training miles per week. He even placed 12th at the 2000 Summer Olympic trials. His personal best time in the marathon is 2 hours, 19 minutes.

"I'm not as young as I used to be, and it's just not as easy running seven days a week as it once was, especially in the winter on a hard, frozen surface," said Mortenson, who placed second in the 10K at last year's national championships in Vermont. He'll again compete in the 10K in Eau Claire. "Running on snow with snowshoes definitely cushions the blow and is easier on your body. It's also peaceful to run and race in a natural setting. I try to run in as many events as I can throughout the winter. If you're willing to drive, you can find a snowshoe race pretty much every weekend."

Katy Class of Woodbury started snowshoe racing four years ago when she met her husband, Rob, who, like her, has always been an active endurance athlete. Class says snowshoe racing is "a big part of their winter lifestyle."

"We take our vacations, like to last year's nationals in Vermont, around the races," she said. "For one thing, it's just plain fun and something different to do in the dead of winter. For another, you get to meet so many wonderful people who you may only see once or twice a year. It's a very unique, close-knit community. And some are very elite athletes and runners."

Class, who regularly competes in marathons and triathlons, said she loves the physical challenge of snowshoe racing.

"It's the hardest sport I've ever done or competed in," she said. "It stresses every part of your body, fires all your core muscles, explodes your heart rate and burns a lot of calories very quickly. It's taxing, to say the least."

As for Graupner, he said he hopes to snowshoe and race as long as possible and is looking forward to this weekend.

"The nationals are really a celebration of snowshoe racing across a wide age spectrum, and I'm just fortunate to be a part of it," he said. "I don't know how I'll do, but I'm just going to go for it and see what happens. The only thing I know for certain is that I'll be good and tired after the race."

Tori J. McCormick is a Prior Lake-based freelance writer. Contact him at torimccormick33@gmail.com.