Kimberly Fowler talks about her new book Flat Belly Yoga, produced with the editors of Prevention Magazine. Flat Belly Yoga combines muscle strengthening, improved flexibility, and interval training exercise. "Yoga is known for relaxation and flexibility benefits, but it's also a full-body workout that strengthens and lenghtens your core muscles," says Folower, founder of YAS Fitness Centers. "When you add light weights, you'll amp up yoga's belly-firming power by boosting calorie burn, revving metabolism, and building calorie burning muscle mass, all of which add up to a leaner tighter core."