Week 3 features more crunches and a challenging move to target your lower abs. Check out David Kirsch's plan below.LOWER BACK CHALLENGE (left) Rest your lower abs on a stability ball and place your palms on the floor. Exhale as you lift your legs until they are in line with your hips. Hold ten seconds, then open your legs wider and hold for ten seconds. Bring your legs back together, hold ten seconds, then lower. Repeat 10 times.
REVERSE OBLIQUE CRUNCH (right) Lie on your back with a stability ball between your knees and shins. Extend your legs to form a 90-degree angle with your torso. Exhale as you curl your tailbone toward your navel and rotate your legs, bringing your left foot and knee closer to your torso, and right foot and knee farther away. Lower and repeat on the other side. Continue to alternate right and left 20 to 30 times.Read MoreLess