When it comes to strengthening your abs, keeping it simple is key. These core exercises are classic for a reason.

By By Mary Anderson
Photo: Pollyana FMS / Getty Images

Two exercises keep proving to be gold standards of core strengthening: the crunch, which firms the more superficial abs-the rectus abdominis down the center and the obliques along the sides-and the plank, which works the deep, corset-like transverse abdominis. (Try these plank variations to torch your core from all angles.)

The crunch is so effective at activating these superficial muscles because their fibers all have a vertical orientation that lets them be in sync with the exercise's straight-up motion, says Martin Eriksson-Crommert at Örebro University in Sweden. His research found that women who place their hands behind the head-instead of atop the chest or reaching forward-get the biggest activation. Speeding up the pace of crunches can double the activation of the rectus, other research has shown. Add a twist to further engage obliques.

Now, about those planks. The variations shown here-plus the core-stability challenge of the double-leg stretch-elicit transverse activation that goes off the charts, according to lab research by Shape Brain Trust member Michele Olson, Ph.D., a senior clinical professor of sport science at Huntingdon College in Alabama who has tested ab exercises for over 20 years. Work them in with your crunches or any of the ab-focused routines and tips in this story for your fittest, firmest core. (And it's not just about getting a six-pack; here's why it's so important to have a strong core.)

Photo: Rony Shram
  • Spider Plank: Start on floor in plank, balancing on hands and toes. Keep hips level and bend left knee out toward left triceps [shown, left]. Return to plank, switch sides, and repeat to complete 1 rep. Do 2 sets of 10 to 12 reps.
  • Double-Leg Stretch: Lie faceup on floor with arms by sides. Curl head and shoulders off floor, then raise arms overhead (biceps by ears) and legs up at 45-degree angle to start. Keeping upper body lifted throughout, bring knees toward chest and circle arms around, touching palms to outside of knees [shown, center]. Extend legs and raise arms overhead to starting position to complete 1 rep. Do 2 sets of 10 to 12 reps.
  • Side Plank Twist: Start on floor in side plank position, balancing on left palm and sides of feet, right foot in front of left; bend right elbow and place palm behind ear to start [shown, right]. Rotate torso to bring right elbow to inside of left elbow. Return to starting position to complete 1 rep. Do 12 reps. Switch sides; repeat. (Want to keep going? Try the 10-minute abs workout Tone It Up's Karena and Katrina swear by.)

Routines with Built-in Core Tighteners

Certain workouts double as strength sessions for your abs. "When you increase your intensity or load during total-body movements, your ab muscles naturally brace," Olson says. "That action really works the transverse." Here's the way to multitask.

  • Swing a kettlebell. Your transverse braces to stabilize your core as you bring the kettlebell's swing to a full stop, especially during one-handed moves.
  • Lift bigger dumbbells. Add a little more heft to your reps-weighted squats, biceps curls, yes, you name it-and "the heavier the load, the more bracing will occur," Olson says. (On that note, here are eight benefits of strength training.)
  • Do sprintervals. Your abs will engage as you pump your arms harder, and the HIIT will help burn more ab fat than if you stuck with steady cardio.

Comments (4)

March 24, 2019
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