The star of the upcoming Rock the Kasbah, who turns 36 this month, has a core you just can't ignore. Credit her 15-year Pilates practice with trainer Nicole Stuart, and in particular the belly-sculpting Criss Cross move. This exercise, which works the entire midsection but especially the obliques, will always challenge you because it never gets easier, Stuart says. Do 10 reps a day to see a flat, toned belly in as little as a month.

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How to do it: Lying faceup, pull knees into stomach. Place hands behind head and bring elbows and knees to touch, or as close as possible (A). Bring left knee to right elbow, pressing both together as hard as you can, and extend right leg (B). Hold for 3 long counts, then return to "A" and hold. Repeat motion with right knee and left elbow while extending left leg. This is 1 rep.

Illustration: Remie Geoffroi

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