The latest research, rolled into the ultraeffective, 20-minute workout

By Selene Yeager for Prevention

In the endless quest for a flat belly, you’ve likely done hundreds (if not thousands) of crunches and balanced in plank poses for hours. And let us guess: You still don’t have flat abs, right? Well, we have news for you: Research shows that it’s not your fault. The way most of us have been cued to do crunches just doesn’t work. That’s the news flash for a recent exercise study that found it’s possible to get twice as much belly-flattening muscle activity from every crunch.

“The way most people do crunches doesn’t work the rectus abdominis (front abdominal muscle) effectively. That’s why you can do thousands and not see much benefit,” says abdominal activity researcher Gilbert M. Willett, a physical therapist at the University of Nebraska Medical Center of Omaha.

Testing ways to put more punch in every crunch, Willett and colleagues monitored the muscle activity of 25 people while they did crunches following different sets of instructions, such as pushing the belly out or pulling it in, or no instructions at all.

They found that when testers sucked in their abs before curling off the floor, they generated twice as much muscle activity as when they didn’t prep their abs. “They not only worked their front abdominal muscles but also the oblique muscles on the sides, which help you look trimmer through the waist,” says Willett.

That simple yet potent tip got us thinking: What if we could find the best belly-flattening advice science had to offer and rolled it into one ultra-effective, easy-to-do program? After poring through research and scientific reviews, even we were surprised by all the tricks and tips that can maximize the belly-flattening power of exercise.

The Flatten Fast Plan
Unlike traditional belly-flattening plans, this routine includes all the key elements to target your entire core - - front, lower back, mid-back, and sides - - from every angle to sculpt a tight, trim torso. The best part: You won't only look better, you'll feel better, too. "Back problems aren't just from major traumatic events, like picking up heavy objects," says exercise researcher David Behm, PhD. "More frequently, they're from simply moving or flexing with poor posture and a tired, out-of-shape back." A strong core can prevent both.

Do the following 20-minute workout 3 nonconsecutive days a week. Perform two sets of the specified number of reps for each exercise, allowing 1 minute of rest between sets. On days you don't do the routine, keep your body moving with cardio activities such as walking, swimming, or cycling to burn more calories and shed excess belly fat.

Diamond Crunch
Lie face up on floor, knees open to sides, soles of feet together. Clasp hands and extend arms over chest. "Hollow" stomach by pulling navel toward spine. Then lift head and shoulders off floor, reaching as far forward as comfortably possible. Hold for a moment, slowly lower to start position, and repeat. Perform 15 to 25 reps.

Double Twist
Sit on floor with knees bent and hands clasped just above thighs. Keeping back straight, lean back slightly, tighten abs, lift feet off floor, and balance. Rotate upper body to right, bringing hands as close to floor as possible, while simultaneously dropping knees to left (opposite) side. Return to center and repeat. Perform 10 twists to left, then repeat to right.Keep both feet on floor as you dip.

Kneeling Side Kick
From a kneeling position, lean to right and place right hand on floor directly beneath shoulder. Extend left leg out to side so it's parallel to floor, foot pointed. Place left hand behind head. Contract abs and bend left leg, pulling knee toward chest. Straighten leg and repeat. Perform 15 to 20 reps. Switch arms and legs and repeat.

Extend 'n' Curl
Kneel on all fours with hands directly beneath shoulders and knees directly beneath hips. Keep back straight and head in line with spine. Simultaneously raise left arm and right leg, extending them in line with back so fingers are pointing straight ahead and toes are pointing back. Then contract abs and draw left elbow and right knee together beneath torso. Extend and repeat. Perform 10 reps, switch arms and legs, and repeat.

Ab Pike
Lie faceup with arms at sides. Bend legs so feet are off floor, thighs over hips, and heels near glutes. As you "hollow" abs, straighten legs and lift hips up off floor. Hold for a moment and slowly lower back to start, bringing hips down and bending legs. Perform 10 to 15 reps.