Work the obliques, plus abs muscles you never knew you had, with this hardcore abs workout.
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Want strong abs muscles? Simply striving for a six-pack isn't the answer: A six-pack only involves one abdominal muscle, when there are actually four key muscle groups you need to focus on for a strong core. The best hardcore abs workouts don't just hammer that one muscle, but rather hit them all.

"For the best results, both aesthetically and functionally, you need to target all the muscles in your abdomen," explains Joan Pagano, an ACSM-certified exercise physiologist and NYC-based trainer.

Here's a breakdown of your abs 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. Toning these creates a "natural girdle" to keep your stomach tucked and stabilize your pelvis, says Pagano. Then, of course, there's the most superficial muscle group in the abdomen: the rectus abdominis, aka the muscle you see when you imagine the classic "six-pack" abs. This set runs from sternum to pelvis, helping you flex your spine while walking. (More here: The Complete Guide to Your Abs Muscles)

One move alone does not target all these muscles. Complete, hardcore abs workouts include a variety of exercises that hit each area. Here, the best hard abs moves to target all areas are demonstrated by Caroline Gogolak, co-founder of Carbon38 and founder of Saint Art.

At first glance, these exercises might not seem like the makings of the most hardcore of abs workouts. It's up to you to scale them to your fitness level. You can always increase your reps, decrease your rest times, or repeat the whole thing over again to create more of a challenge. Go at your own pace, doing the number of reps and sets that works best for your body. (Next up: Tackle our 30-day abs workout challenge.)

1. Roll-Back

woman demonstrates roll back abs exercise

Works: Rectus abdominis

A. 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 facing one another.

B. Exhale, drawing navel toward spine while rolling 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

woman demonstrates twisting roll back abs exercise

Works: Internal and external obliques, rectus abdominis

A. With arms extended forward, do a roll-back, curving spine into a "C" shape. 

B. Twist torso to the right, bending right elbow and pulling it back at shoulder level while reaching left arm to right knee.

C. Reach both arms forward and return to starting position. Switch sides; repeat. Continue alternating.

3. Medicine Ball Sit-Up

woman demonstrates medicine ball roll back abs exercise

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

A. Hold a medicine ball overhead and recline all the way down to the floor.

B. Lift from core back to a sitting position, keeping the ball overhead.

Scale up: To make this more challenging, find a slant board at the gym, or buy one. Hook feet under the top of the board. The downhill slant and extra weight add an extra challenge to abs muscles. Increase the angle of the board and the weight of the ball for more of a challenge.

4. Kneeling Crunch

woman demonstrates kneeling crunch abs exercise

Works: Rectus abdominis, internal and external obliques

A. Kneel with right arm stabilized directly under shoulder, reaching left arm forward at shoulder level and right leg back at hip height.

B. Exhale, contract abs, and round back up to the ceiling while drawing left elbow to right knee, turning palm up. Do one set, then switch sides; repeat.

5. Dead Bug

woman demonstrates dead bug abs exercise

Works: Transversus abdominis, internal and external obliques

A. 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.

B. Exhale, lowering left arm and right leg toward the floor, bringing left knee in over chest. Keep low back connected to the floor at all times — don't arch. Switch sides; repeat.

6. Lunge Split Jacks

woman demonstrates lunge split jump abs exercise

Works: Rectus abdominis

A. Stand with feet in a staggered stance, left foot two to three feet in front of right foot, then lower body into a split squat.

B. Jump up and scissor-kick legs, landing with right leg two to three feet in front of left. As soon as feet land, lower body into a split squat. Continue alternating.

7. Toe Dip

woman demonstrates toe dip abs exercise

Works: Transversus abdominis

A. Sit tall with both knees bent in front of body, 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.

B. Lift legs so that knees are bent over hips with calves parallel to the floor. Inhale and dip left toes to the mat while maintaining right angles at the knees.

C. Exhale, then return to starting position. Switch sides; repeat. Continue alternating.

8. Bicycle Crunches

woman demonstrates bicycle crunch abs exercise

Works: Internal and external obliques, transversus abdominis

A. Lie flat on the floor with lower back pressed to the ground; pull abs downward to target deep abs muscles. Interlace fingers and put hands behind head. Start by bringing knees in toward chest, lifting shoulder blades off the ground.

B. Straighten left leg out to about a 45-degree angle from the ground while turning upper body to the right, bringing left elbow toward right knee. Make sure ribcage is moving, not just elbows.

C. Switch sides; repeat. Continue alternating, creating a "pedaling" action. Do this exercise with slow and controlled motion.

9. The "Jean-Zip"

woman demonstrates jean zip abs exercise

Works: Transversus abdominis

A. As if 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 muscles.