Peruse any fitness mag or website, and you’ll see lots of six packs. Not the kind you find in your fridge — the chiseled ab type.

No matter how many crunches and planks some of us do, that six pack remains hidden in the back of the fridge (which means behind a layer of fat). If that’s your goal and it’s not happening, it may be due to the way you’re training.

“In order to lose weight and show muscle definition, you need to train the whole body,” says Amanda Butler, a certified trainer based in NYC. “[You need] to expend calories — and pair that with a well-balanced diet.”

“It is important to train the core because that is your center for balance,” Butler says. “Plus, a strong core can help reduce back pain.”

To eliminate the guesswork in hitting those specific muscles, we asked Butler to share the most effective lower ab exercises. Just don’t blame us if it hurts to laugh the day after this routine.

Perform each exercise for 30 seconds, with 10 seconds of rest between moves. Complete the entire circuit 1 to 3 times.

1. Heel tap

To do this exercise:

  • Lie faceup with your arms to your sides and hands against the floor.
  • Bend your knees, keeping your calves parallel to the floor.
  • Slowly lower your flexed feet forward until your heels barely touch the floor.
  • Squeeze your abs to help raise your feet back up to the starting position.
  • Continue to repeat for 30 seconds.

2. Mountain climber

To do this exercise:

  • Start in a high plank position with your body straight and your hips level.
  • Lift your right foot and draw your right knee toward your chest in between your hands. Keep your core tight and try not to hike your hips.
  • As you return your right leg to plank, lift your left foot and draw your left knee to your chest between your hands.
  • Continue to alternate legs as quickly as possible for 30 seconds.

3. Scissor

To do this exercise:

  • Lie faceup with your hands behind your head and your head and your shoulders lifted off the floor.
  • Using your abs, lift your legs slightly off the floor and scissor kick with one leg up and one leg down.
  • Alternate your legs for 30 seconds. Don’t strain your neck or jut your chin forward.

4. Slider pike

To do this exercise:

  • Grab some sliders, coasters, or towels to put under your feet.
  • Start in high plank position with both feet on the sliders.
  • Squeeze your low abs and pull your feet in toward your hands, lifting your hips up toward the ceiling into a pike position.
  • Slowly push your feet out to lower your back into the starting position.
  • Repeat for 30 seconds.

Note: To make this move easier, do sliding mountain climbers, moving 1 leg forward at a time.

5. Straight leg raise

To do this exercise:

  • Lie faceup with your arms to your sides and hands against the floor.
  • Brace your core and lift your straight legs slowly off the floor, bringing them to 90 degrees.
  • Slowly lower your legs back to the floor.
  • Repeat for 30 seconds.

Note: If you have any pain in your lower back, don’t do this move, or try this pull-up bar variation instead.

  • Holding a pull-up bar, brace your core and lift your legs off the floor to hip height. (Beginners can bend their knees; advanced exercisers can keep their legs straight and hinge at the hip for more of a challenge).
  • Slowly lower your legs to the starting position.
  • Repeat for 30 seconds.

6. Cross body climber

To do this exercise:

  • Start in high plank position with your body straight, your hips level, and your core braced.
  • Lift your right leg and draw your right knee in toward your left elbow.
  • As you return your right leg to plank, lift your left leg and draw your left knee toward your right elbow.
  • Continue to alternate legs for 30 seconds.

7. Slider knee tuck

To do this exercise:

  • Grab some sliders, coasters, or towels to put under your feet.
  • Start in high plank position with both feet on the sliders.
  • Brace your core and pull both feet in toward your chest. Avoid hunching your shoulders or allowing your upper body to lean forward too much.
  • Push your feet back to return to the starting position.
  • Repeat as many times as you can in 30 seconds.

Exercise ball variation

If you have an exercise ball handy, try this variation instead:

  • Start in plank position with your feet on the ball.
  • Keeping your core engaged, draw both knees in toward your chest.
  • Slowly extend your legs back to the starting position.
  • Repeat for 30 seconds.

8. Rolling plank

To do this exercise:

  • Start in low plank position propped up on your forearms.
  • Hold for 10 seconds.
  • Roll onto your right elbow, stacking your feet.
  • Hold side plank for 10 seconds, engaging your obliques.
  • Roll back through center and onto your left elbow, stacking your feet.
  • Hold for 10 seconds.
  • Continue to alternate, keeping your core engaged and not letting your hips drop, for 30 seconds.

9. Roll up

To do this exercise:

  • Lie faceup with your legs extended, knees together, feet flexed, and arms straight overhead.
  • Take a big inhale.
  • As you exhale, lift your arms up and forward and use your abs to slowly roll up to a sitting position.
  • Drawing your abs in, slowly lower back to the starting position.
  • Repeat as many times as you can in 30 seconds.

10. Jackknife

To do this exercise:

  • Lie faceup with your legs extended, feet together, and arms raised straight overhead. Inhale.
  • As you exhale, squeeze your abs and raise your right arm and left leg, touching your hand to your foot.
  • Inhale and slowly lower back to the starting position.
  • Repeat for 15 seconds.
  • Repeat on the opposite side for 15 seconds.

Here are a few other exercises to rotate into your routine, or add to the mix when you need an extra ab boost. Do each exercise for 30 seconds.

11. Flutter kick

To do this exercise:

  • Lie faceup with your legs extended, toes pointed, and hands tucked under your glutes to support your lower back.
  • Lift both legs a few inches off the floor.
  • Alternately kick your legs up and down.
  • Repeat for 30 seconds.

12. Reverse crunch

To do this exercise:

  • Lie faceup with your arms at your sides and your palms facing the floor.
  • Bend your knees so your hips and knees form 90-degree angles.
  • Activate your lower abs to lift your hips off the floor, bringing your knees toward your chest.
  • Lower back down to the starting position as slowly as possible to keep your lower abs engaged.
  • Repeat for 30 seconds.

13. Firefighter

To do this exercise:

  • Stand with your feet shoulder-width apart and your core engaged.
  • Shift your weight onto your right leg and lift your left knee, bending your left leg to a 90-degree angle. Keep your arms in front of you as if you’re climbing a ladder.
  • Extend your left arm overhead as you push off your right foot.
  • Explosively lift your right knee until it’s level with your hips.
  • Pull your hand down as you lower your right leg.
  • Repeat on the other side.
  • Continue alternating your legs and arms as fast as you can for 30 seconds.

14. Hollow body hold

To do this exercise:

  • Lie faceup with your arms by your sides and legs extended.
  • Engage your abs and lift your shoulder blades and legs off the floor.
  • Keeping your lower back pressed into the floor, hover your legs off the floor.
  • Hold this pose for 30 seconds.

15. March with a twist

To do this exercise:

  • Stand with your feet hip-width apart, shoulders down, arms overhead, and core braced.
  • Bring your right elbow to your left knee as you twist through your waist. Use your core to lift your knee and squeeze your obliques.
  • Return to the starting position.
  • Repeat on the opposite side.
  • Continue to alternate sides for 30 seconds.

16. Tuck jump

To do this exercise:

  • Stand with your feet hip-width apart, your core engaged, and your back straight.
  • Send your hips back, bend your knees slightly, and bend your elbows at 90-degrees with your palms facing downward.
  • In one explosive movement, jump up and draw your knees toward your chest so they tap your downturned palms.
  • Land lightly on your toes, with a slight bend in your knees, and immediately jump up again.
  • Jump for 30 seconds.

17. Chair pose twist

To do this exercise:

  • Stand with your feet hip-width apart, your core engaged, your hips back, your knees bent, and your hands behind your head.
  • Rotate your upper body to the right, hooking your left elbow to the outside of your right knee. Don’t allow your hips to twist to the right — instead bring your left rib cage toward your right hip bone.
  • Rotate to the other side.
  • Repeat for 30 seconds.

18. Plank arms walk-out

To do this exercise:

  • Start in a high plank position.
  • Slowly walk your hands forward, so that your wrists are no longer under your shoulders and your body is extended.
  • Walk your hands as far forward as possible.
  • Pause at the farthest point for a moment before walking your hands back to the starting position.
  • Continue to repeat for 30 seconds.

19. Dragon flag

To do this exercise:

  • Find an anchor to hold onto with your arms extended overhead. You could use a chair, bench, or a closed door.
  • Lie faceup with your knees bent.
  • Shifting your weight into your shoulders, engage your core and lift your feet overhead, like a shoulder stand.
  • Try to keep your legs as straight as possible.
  • Lower your legs, without allowing them to touch the floor, then repeat.
  • Do slow, controlled reps for 30 seconds.

Special thanks to our model, Amanda Butler, a certified trainer based in NYC.