The CrossFit craze doesn’t seem like it’s going to die down anytime soon. In fact, according to a recent Fitbie article, this year’s CrossFit Games sold out within days of tickets going on sale. In 2011, spectators didn’t even fill up half of the 12,000-seat venue. So why has the strength and conditioning program—which mixes sprinting, jumping rope, and other forms of high-intensity cardio with functional exercises performed with all sorts of equipment, including barbells, dumbbells, pull-up bars, kettlebells, medicine balls, and more—earned so many devout followers? According to CrossFit Games athlete Cheryl Brost, a 41-year-old mother of two, it’s because…