Recovery is everything.
Credit: Don Emmert / AFP / Getty Images

Despite his insistence on going the extra mile, Demong says that the key to high-level performance is knowing when to call it quits – by taking rest periods, that is. He says that idea is not only crucial, but also among the least understood by non-Olympians. "Amateurs have the hardest time with taking time off," he says. "People get into endurance sports and there's suddenly a feeling that running gives them, a feeling that training gives them, and they want to do more and more." 

Demong knows that when you reach peak conditioning, it's important to recover and let yourself heal so you can reap the benefits of all your hard work come race day. "A lot of times, I'll try to help someone get ready for a marathon, and the last couple of weeks, they're always like 'What do you mean I shouldn't be running these days,' " he says. "They don't realize that they've already done the work; now they just need to rest and recover."