Back in 2002, University of Virginia scientists estimated it would take 250,000 crunches to burn a pound of fat. We're pretty sure the researchers published this statistic to make a point. But after almost a decade, that point still may not have hit home. "I'm amazed at the number of people who think that simply doing ab exercises like crunches and situps will make their belly disappear," says Craig Rasmussen, co-creator of 24-Hour Abs, Men's Health's newest ab-sculpting program. "That's probably the least efficient way to reveal your six-pack."

The real secret: Work every inch of your body, not just your abs. "Muscle is your body's primary fat burner," says Rasmussen. So by choosing the right exercises -- multi-muscle movements that burn lots of calories, but that also simultaneously train your core -- you can truly carve out a washboard. And you can start today, with these 3 genius "ab" exercises.

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1. Mountain Climber with Pushup
Why it works: Sure, the pushup is a great movement for your chest, shoulders, and triceps. But it's also a great core exercise. Why? Because to do it right, your core muscles have to work over time to keep your spine stiff, according to a recent Canadian study. And when you combine this classic move with an ab exercise called the mountain climber, it engages your core even more. Watch the video to see how to do the exercise with perfect form. Try doing to 10 to 12 reps, or simply perform sets for 30 to 60 seconds at a time. And for more ways to improve the pushup -- and other classic moves -- discover these 18 Exercise Upgrades.

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2. Turkish Getup
Why it works: When people first hear of the "Turkish getup", their typical reaction is to chuckle. Then they try the exercise. No one chuckles after that -- at least not if they do it right. At its core, the Turkish getup is a super-simple movement: You lie on your back, holding a kettlebell or dumbbell above one shoulder. Then you simply stand up, while keeping the weight above you at all times. This not only helps build total-body strength -- including your core -- it’s also a great way to torch calories. But as simple as it sounds, there are plenty hard-to-notice details that can help you get the most out of this move. So watch the video to learn the seven steps of the Turkish getup. A good place to start: Do 3 reps -- or "getups" -- with each arm; rest 60 seconds, and repeat one more time. As fitness expert David Jack says: "Get this exercise right, and it will do amazing things for your body." (On the flip side, there are surprising things that can hurt your body: Find out How High Heels Can Make A Woman's Breasts Sag.)

3. Pushup-Position Row with Squat Thrust
Why it works: Now and then, an exercise becomes popular seemingly overnight. That's the case with the pushup-position row, which is a good way to work your back, and even better for strengthening your core. (Every time you row one dumbbell, your core muscles have to fight to keep your body stable.) However, we've discovered a way to instantly make it more effective. In fact, you might think of it as turbocharging this exercise. How? By combining it with the classic squat thrust. This boosts the demand on your cardiovascular system and increases your calorie-burn, helping you melt belly-fat as you sculpt your abdominals. Try doing this exercise for 30 to 60 seconds, then rest 30 to 60 seconds and repeat one to two times. And don't forget the old fitness joke: To really lose belly-fat, you'll need to also perform the "plate push-away." That is, you need to push your plate away before you eat too much -- especially when you're faced with one of these 25 Healthy Foods That Aren't.

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-- Additional reporting by Maria Masters

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