There are two steps to achieving a narrow waist: lower your body fat and build up the girdle of abdominal muscle that holds in your internal organs. If your body fat percentage is high, reduce your calorie intake and perform aerobic exercise. A number of exercises can tone your waistline by building muscle.
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The best way to build core strength isn't with ab-specific exercises, but with big, compound lifts like the deadlift and squat, according to a study published in a 2008 issue of "Journal of Strength and Conditioning Research." It may seem counterintuitive that lifting heavy weight can actually narrow your waist, but this occurs because of a process called abdominal blocking. All of the abdominal muscles activate in order to create internal pressure that prevents the spine from folding forward. This develops your core muscles such that even when they are relaxed, they hold in your internal organs better, giving you a slimmer waist.
Squats are another exercise that stimulates the kind of core development that narrows the waist. The key is to expand your ribcage and abdominal muscles, and to perform the exercise in a slow, controlled manner. If you doubt that it's possible to lift heavy weight and not develop a large waist, just look at eight-time Mr. Olympia Arnold Schwarzenegger. In his classic book, "The New Encyclopedia of Modern Bodybuilding," he explains that in order to develop his huge thighs, he regularly performed squats with 500 lbs. for multiple reps. And yet, it was the contrast between his huge muscles and his tiny waist that truly made him a champion.
Once you've worked heavy, compound exercises into your regimen, perform some abdominal-specific exercises. Cranking out hundreds of crunches, however, is inefficient. The American Council on Exercise decided to find out which ab exercises really work, so it funded a study and published the results in the May 2001 issue of "Fitness Matters." The study found the exercise that recruited the most effort from the rectus abdominis, the wall of muscle that creates the six-pack, is the bicycle crunch. It causes the rectus abdominis to work 2 1/2 times as hard as during standard crunches. The captain's chair crunch came in second, being twice as effective as a standard crunch.
Captain's Chair Crunches
The ACE study reports when it comes to the oblique abdominals, which narrow the waist by cinching it in at the sides, the captain's chair crunch is the No. 1 exercise, stimulating triple the oblique abdominal activity. The bicycle crunch came in second, causing not quite three times the activity.