What drives an extreme athlete? Find out from Ellyn Brown, a 54-year-old Alaskan who is the U.S. mountain running champ and one of the best snow shoe racers alive.

Many try -- not all succeed. But it seems that these days, the biggest names in mountain climbing are people over the age of 50! In fact, a group of 70-year-olds is hoping to smash the record for climbing Mount Everest.