You eat well, do cardio, and crank out countless crunches, but you still don't have a flat belly? Add some Pilates moves to your routine. When researchers at Auburn University measured muscle activity in the abs during a hundred, double-leg stretch, crunch, and roll-up, they found that the first two were tops for targeting the transverse abdominis. "That's the deepest ab muscle, which pulls in the midsection and stabilizes the spine, giving you a flatter belly as well as more control during exercise and everyday movements," says lead author Michele Olson, Ph.D., professor of exercise physiology at Auburn University. "Plus, the more stable your spine, the better your posture." Keep up the healthy eating and cardio, but mix up your ab exercises too. By combining Pilates moves and traditional toners, you can create a rut- and gut-busting workout that emphasizes all your middle muscles.