On Monday morning, Dallas Bakken was warming up in front of the Kincaid Park chalet, sprinting a handful of strides, stopping, then sprinting back.

"I'm the best snowshoer in the world," he called happily as he sprinted off, his snowshoes flopping on the hard-packed snow. "Meet me at the finish line."

Wednesday afternoon, the Bismarck, N.D., athlete was leading his division of the 400 meters when he fell to his knees at the top of the home stretch. One snowshoer passed him, then another, then another until they were all past. Bakken stayed down. One by one, the others crossed the finish line. Bakken stayed down.

A man and a woman in red jackets with "medical" written across the backs ran down to where Bakken knelt. When they reached him, Bakken waved them off. He struggled to his feet and limped slowly down the long straight stretch. It took him two minutes to cover that last 80 meters, as people applauded and shouted encouragement.

The medics met Bakken at the finish line and carried him into the athletes' tent. Ten minutes passed. The medics carried Bakken out, put him on the back of a six-wheeled John Deere and drove him away, a splint on his right leg.

"He'll be fine," his mother said later. "They thought his knee felt a little mushy. But later they checked the other one and it was the same. They said that's just the way his knees are."