You won't find the Swiss ball peddled on late-night infomercials, but it may be one of the best power tools for sculpting your abs. The soft, unstable surface challenges your core to work even harder and helps improve your balance and coordination, says David Jack, owner of Activ8 in Phoenix, Arizona, and creator of 30 Days to Ripped. One of his favorite core-chiseling moves to perform on the ball: the jackknife. It recruits your entire midsection, which includes your hip flexors, lower back, glutes, obliques, lower abs, and six-pack muscles. Oh, and you’ll also work your shoulders and legs, too. Ready to try it? Watch the video below to learn how to perform the move with perfect form.

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Incinerate fat and sculpt every muscle with the revolutionary new DVD fitness system from Men's Health: 10-Minute Torchers.

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