Bob Karch is the chairman and a professor in the Department of Health and Fitness at American University. Here, he helps cross-country champion Steve Hallinan check his heart rate while cross-training on the bike. Allison Aubrey/NPR hide caption

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University of Florida quarterback Tim Tebow embraces his mother, Pam, during a November 2009 pre-game ceremony before an NCAA college football game against Florida State. The two are set to appear in a controversial anti-abortion ad that will air during the Super Bowl. Phil Sandlin/AP hide caption

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Lowell Bailey (in purple), Bill Demong (bib 61) and Tim Burke (bib 37) competed against each other when they were 9 and 10 years old — and now they're headed to the Winter Olympics in Vancouver. Courtesy of the Demong family hide caption

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Ski cross skiers at the Nature Valley World Cup ski cross final in Lake Placid, N.Y. Graham Smith/NPR hide caption

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