Unless you didn't get the memo from the nearly-nationwide heat wave last week, it's go time for getting flat, bikini abs. To the rescue: FITNESS is sharing the latest core science and lab-tested exercises in part three of our Body Lab series in the April issue (on newsstands now). And talk about total tummy transformations! Testers who did the workout three times a week and followed the 1,500-calorie-a-day diet lost up to three inches from their waistlines in four weeks! Not only can you try the workout in the magazine, but you can also do it with the creator—and model—herself, instructor Chelsey Korus at YogaWorks studios in New York City. If you've read the article already, you know that it's Korus's perfectly chiseled six-pack which is featured throughout it. And the workout is definitely getting buzz—Korus tells us that a friend even spotted a copy of the April FITNESS at Barnes and Noble with her "Core Knowledge" story torn out. "I consider that the highest form of flattery," she says. Korus is now infusing each of her classes at YogaWorks in New York City with the ab moves, and is already seeing a difference in her students. "They're asking for the tolasana [see photo above] in class so they can show me their progress!" If you're in the NYC area, find her YogaWorks schedule here and take the challenge yourself.