Toned Backs

Rosario DawsonRosario Dawson. Photo by Steve Granitz/WireImageGET THE LOOK: Justin Timberlake has an influence among leading ladies because they all want their sexy back! And Rosario Dawson certainly got hers, making the perfect backdrop for her equally sexy backless dress. INSIDER TRICK: Celebrity trainer Tim Davis, of Peak Performance in N.Y.C., helps stars sculpt their upper back with the "bent over reverse fly" exercise. Stand with knees slightly bent and torso parallel to the floor. Holding a 5-pound weight in each hand, bring straight arms up and out to your sides, making your body look like the letter T, and bring arms down. Repeat 15 times every other day. BUY ONLINE NOW: All Pro 5-Lb Chrome Dumbell Set, $30 -Polly BlitzerCheck out In Style contributing editor Polly's Web site,