How This Workout Works Whether you're curious about CrossFit or have already been bitten by this drenched-in-sweat sculptfest, its body-transforming allure couldn't be more off the hook. "In 20 minutes you incinerate major calories and fat, plus you boost every facet of fitness, such as strength, balance, endurance, and speed," says Megan May, the head trainer for Reebok CrossFit 5th Ave in New York City.