Through constant training, mountain guide and climber Jason Antin has conditioned his body to achieve extreme goals. He once summited Denali twice in the same week from different approaches. He has also completed the Rainier Infinity Loop, which involves two summits of Rainier and a circumnavigation of the entire mountain on the Wonderland Trail. Antin grew up in Massachusetts and now lives in Colorado, where he trains athletes to build their strength and endurance for the mountains. He regularly hikes while carrying one—or both—of his kids.