Everybody wants a six-pack-which is great. But FYI, there are actually four key muscle groups you need to tone to get a taut tummy. (On a deadline? This workout is the fastest way to lose belly fat.)

“For the best results, both aesthetically and functionally, you need to target all the muscles in your abdomen,” explains NYC-based trainer Joan Pagano, author of Strength Training Exercises for Women.

What are they? Let’s meet all your ab muscles.

On the side of your abs, you have your external abdominal obliques and your internal abdominal obliques. Your external obliques lie on top, and are those muscles you feel in your side, just under your arm. The internal obliques are deeper muscles that lie underneath your external obliques, acting as stabilizers to help you maintain your posture.

The transversus abdominis are your deepest muscles, running horizontally around your midsection. Pagano says that toning these creates a “natural girdle” to keep your tummy tucked and stabilize your pelvis. Then, of course, there’s the most superficial muscle group in the abdomen: the rectus abdominis (when toned, the classic “six-pack” abs). This set runs from sternum to pelvis, helping you flex your spine while walking.

One move alone does not tone all these muscles. You’re going to need at least a few weapons in your arsenal to tighten up all over. Here, Carbon38 cofounder Caroline Gogolak demos the best hard abs moves to target all areas-even the ones you can’t see. (Next up: Tackle our 30-day abs workout challenge.)

1. Roll Back

Works: Rectus abdominis

Pagano says: Sit up straight, with knees bent at 90 degrees and feet flat on the floor. Pull torso in close to thighs, reaching arms forward at shoulder level with palms down. Exhale, drawing navel toward spine as you roll back onto tailbone, curving spine into a “C” shape. Inhale and realign spine to straighten up. (Want more? Continue with the best exercises for lower abs.)

2. Twisting Roll Back

Works: Internal and external obliques, the rectus abdominis

Pagano says: With arms extended forward, perform a roll-back, curving spine into a “C.” Twist torso to one side, bending one elbow and pulling it back at shoulder level while reaching other arm to opposite knee. Reach both arms forward and return to starting position. Repeat on the other side.

3. Medicine Ball Sit-Up

Works: Transversus abdominis, rectus abdominis, internal and external obliques

Personal trainer Jimmy Minardi says: Hold a medicine ball over head, and recline all the way down. Lift from core back to a sitting position, keeping the ball over head. To make this more challenging, find a slant board at the gym, or buy one for around $50. Hook feet under the top of the board. The downhill slant and extra weight add an extra challenge to ab muscles. Increase the angle of the board and the weight of the ball for better results.

4. Kneeling Crunch

Works: Rectus abdominis, internal and external obliques

Pagano says: Kneel with one arm stabilized directly under shoulder, reaching other arm forward at shoulder level and opposite leg back at hip height. Exhale, contract abs, and round back up to the ceiling while drawing elbow to knee, turning palm up. Repeat on the other side.

5. Dead Bug

Works: Transversus abdominis, internal and external obliques

Pagano says: Lie on back with legs raised, knees bent over hips and calves parallel to the floor. Extend arms to the ceiling with palms forward, and pull abs tight, bringing navel to spine. Exhale, lowering opposite arm and leg toward the floor, bringing remaining knee in over chest. Keep low back connected to the floor at all times-don’t arch. Repeat on the other side.

6. Lunge Split Jacks

Works: Rectus abdominis

Minardi says: Stand with feet in a staggered stance, left foot in front of right, 2 or 3 feet apart, then lower body into a split squat. Jump up and scissor-kick legs, landing with right leg forward. As soon as feet land, lower body into a split squat.

7. Toe Dip

Works: Transversus abdominis

Pagano says: Sit tall with both knees bent in front, feet flat on the floor. Lean back onto elbows with shoulder blades down and together. Tighten abs, sliding hands under lower back for support with palms facing down. Lift legs so that knees are bent over hips with calves parallel to the floor, inhaling and dipping toes to the mat while maintaining those right angles at the knees. Exhale, then return to starting position.

8. Bicycle Crunches

Works: Internal and external obliques, transversus abdominis

Minardi says: Lie flat on the floor with lower back pressed to the ground; pull abs downward to target deep ab muscles. Interlace fingers and put hands behind head. Start by bringing knees in toward chest, lifting shoulder blades off the ground. Straighten right leg out to about a 45-degree angle from the ground while turning upper body to the left, bringing right elbow toward the left knee. Make sure ribcage is moving, not just elbows. Repeat on the other side. You should be creating a “pedaling” action; do this exercise with slow and controlled motion. (Complement bicycle crunches with the Muffin Top Melter plan-results are self-explanatory!)

9. The “Jean-Zip”

Works: Transversus abdominis

Pagano says: You can do this move discreetly, at any time throughout the day. As if you were zipping up a tight pair of jeans, “scoop abs” by pulling navel in toward spine and then up, lifting the pelvic floor. This move engages those deep abdominal muscle to flatten the belly-it’s the muscle that lies right under your zipper. (Exercise is key, but if a taut tummy is what you’re after, some overall lifestyle changes might be in order. Luckily, you can lose belly fat in 14 days with just a few key tweaks.)

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