The (15 Minute) Belly Blasting Workout

Even women who are otherwise slender and fit can end up with a belly pooch due to underworked lower abdominal muscles. This workout will tap into the deep abdominal muscles—the transverse abdominis—that pull in your waistline like a corset. Do these moves one after another with no rest in between. Then repeat the circuit so you're performing it a total of two times.

Stability Ball Pelvic Tilt Crunch

Grab a five-to 10-pound medicine ball (or dumbbell). Lying faceup on a stability ball with your upper back and head pressed against the ball and your feet together on the floor, hold the medicine ball against your chest. Brace your abs and crunch up until your shoulders are off the ball. Then reach the ball toward the ceiling. Lower it and return to the starting position. Do 12 to 15 reps.

Tip: Control your movement through the entire exercise, bracing your core and keeping your back flat.

MOVE 2Stability Ball Mountain Climber

Assume a plank position with your hands shoulder-width apart on a stability ball. Draw your right knee toward your chest. Hold for one second, then return to the plank position. Repeat with your left knee. That's one rep. Do 12 to 15 reps.

MOVE 3The Matrix

Grab a five-to 10-pound medicine ball (or dumbbell) and kneel on the floor with your knees hip-width apart. Keep your torso upright and hold the ball against your abs. Slowly lean back as far as possible, keeping your knees planted. Hold the reclined position for three seconds, then use your core to slowly come up to the starting position. Do 12 to 15 reps.

MOVE 4Arm Pull-Over Crunch

Grab a pair of dumbbells and lie on your back with your arms above your head. Lift your legs to a 45-degree angle. Bring your arms over your chest and lift your shoulders up while lifting your legs up perpendicular to the floor. Return to the starting position (keep your legs off the floor). That's one rep. Do 12 to 15.

MOVE 5Knee-Cross Crunch

Stand with your shoulders in line with your hips, and extend your left arm up and your right leg to the side, toes pointed. Lower your left elbow and raise your right knee, crunching them together on a diagonal line. Return to the starting position. That's one rep. Do 12 to 15 on each side.

MOVE 6The Sprinter

Lie on your back with your arms at your sides, legs straight, and heels hovering six to 12 inches off the floor. As you sit up, lift and bend your left elbow, and pull your right knee to your chest, as if you were sprinting. Return to the starting position, keeping your legs raised, and repeat with the opposite arm and leg. That's one rep. Do 10 to 12.

MOVE 7Wall Crunch and Twist

Sit on a stability ball, facing a wall. Lie back so the middle to small of your back is resting on the ball. Place your feet hip-width apart on the wall with your knees bent 90 degrees; cross your arms over your chest. Curl up and twist through the waist to the left. Return to center and curl down so your back is parallel to the floor, then twist up to the right. That's one rep. Do 10 to 12.