'Hollaback' your way to a 6-pack

Want rockin' abs like Gwen Stefani? We grabbed Nike Master trainer Rebecca Kennedy (who isn't a celeb but is a star in the fitness world) to create a workout that will teach you exactly how to get abs like Gwen. (If you want more from Rebecca, we've also grabbed some total-body moves to help you feel (and look!) great naked, a routine for a strong and sexy back, and an upper body workout perfect for rocking off-the-shoulder shirts.)

How it works: Do each move for AMRAP (as many reps as possible) in the amount of time given. Rest for 20-30 seconds in between each move. Try repeating the circuit twice.

You'll need: a mat, medicine ball, and a bench (optional)

Hollow Body Hold

A. Lay on the floor in tabletop position (knees directly over hips, shins parallel to the floor), with lower back pressing into floor. Hold the medicine ball in two hands directly over chest with arms outstretched.

B. Extend legs and slowly lower them towards the floor. Stop when the lower back starts to come off the floor. Squeeze abs to hold this position for 30 seconds.

Side Plank

A. Start in an elbow plank position with forearms crossed so that one is in front of the other and they are parallel to the front of the mat. Keep feet together.​

B. Rotate up to a side plank on your right elbow, extending left arm towards the ceiling. Keeps hip lifted. Hold for 4 seconds, then rotate back down to elbow plank with forearms crossed.​

C. Without pausing in elbow plank, rotate up to the left side plank, balancing on the left elbow. Extend right arm towards the ceiling. Hold for 4 seconds. Alternate holding 4 seconds on each side for 45 seconds total.

Plank to Superman

A. Start in a high plank position with shoulders over wrists and core engaged. Slowly lower chest, taking 4 seconds to reach the floor.​

B. Rest body on floor, and extend arms straight forward and legs straight back. Lift them as high off the floor as possible to come into superman. Hold for 4 seconds.​

C. Place palms on the floor under shoulders and push-up back to start position. Repeat for 45 seconds.

Kneeling Rotation

A. Start kneeling on the floor with toes pointed backwards (shoe-laces touching the ground). Place hands behind head with elbows pointing out.​

B. Hinge forward and send hips back over heels, keeping core tight and back straight. Then squeeze glutes to come back to kneeling tall, lift chest and exhale while you rotate to the left. Immediately lower chest again, then raise and twist to the right. Repeat for 45 seconds.

Dolphin Inchworm

A. Start in elbow plank position with shoulders over the elbows. Instead of clasping hands at center, point forearms and fingers straight forward with palms face down.​

B. Walk feet towards hands slowly until hips are overhead. Lift one leg straight up, then the other, then walk feet back out into plank. Repeat for 45 seconds.

Kneeling Woodchop

A. Start kneeling with left knee on the ground directly under the left hip and right knee at a 90-degree angle directly in front of the right hip. Tuck your left toes under to tighten the glute.​

B. Hold medicine ball with two hands up next to left ear and inhale. In one swift motion, swing medicine ball across your body, down to the outside of the right hip and exhale. Repeat for 30 seconds on each side, keeping core tight and breathing throughout the movement.

Forearm Windshield Wipers

A. Start in elbow plank with feet together.​

B. Rotate hips to the right side, coming onto the outside of the right foot. Without pausing, rotate hips to the left side, coming onto the outside of the left foot. Repeat for 30 seconds, keeping core tight and glutes engaged.

Russian Twist

A. Sit on a bench (if available). Sit up tall with toes on the floor (beginner) or hovering off the ground (more advanced), holding medicine ball in front of the belly button.​

B. Rotate medicine ball outside of the left hip, keeping legs stationary. Quickly rotate over to right hip. Continue alternating for 30 seconds.

Bicycle Twist

A. Start laying on bench (if available), with legs extended and lifted off the floor. Place hands behind ears with elbows pointing out.​

B. Pull right knee in so the toe is in line with the left knee. Squeeze abs and rotate to pull left elbow to right knee.​

C. Switch legs so that left knee is pulled towards chest, and rotate to try to touch right elbow to left knee. Be sure to extend legs to straight for each rep. Continue alternating for 30 seconds.

Roll to Jump

A. Start laying on a bench (if available) with arms outstretched overhead. Pull knees in towards chest to roll backwards slightly.​

B. Then quickly roll body forward to sit up, place feet on floor, and come to standing. Once feet have hit the ground, jump straight up with arms overhead.​

C. Keeping arms overhead, sit back onto bench, pull knees to chest and roll onto upper back to start the next rep. Continue for 30 seconds.

Want more core burn? Here are 20 tips and tricks on how to get abs.