Abs-olutely! Summer's Sexiest Six-Packs

From Nick Jonas to Jennifer Aniston to Shakira, see which stars are impressing with their taut tummies

KELLY ROWLAND

The X Factor judge proved her body is her best advertisement when she showed up on the set of her new workout video, Sexy Abs Cardio Sculpt, with a serious six-pack. "I did this whole workout for an hour, five days a week, to prepare," she told PEOPLE. "It is intense while you're doing it. But when you're done you feel incredible."