"How can I trim -- and boost -- my butt for good?"

Smart Solution: Your best lower-body fix is cardio on an incline to burn and firm. "It requires you to extend your hips, which naturally works your glutes," Bryant says. Plus, tackling a killer hill routine sculpts your legs and dejiggles your behind. At a 15 percent incline, you'll burn about 60 percent more calories running and 150 percent more calories walking than you would hoofing it on a flat surface.

Try: Jumping on a stepmill (that revolving staircase at the gym) or hitting the stairs -- they provide steeper climbs, the same as a 62 percent grade on a treadmill, Bryant says. "Even step-ups on a bench or taking a hilly hike will help." To get the most out of your treadmill routine, try FreeMotion's Incline Trainer (heartsmartexercise.com), with a 30 percent incline (most machines top out at 15 percent). Looking for a class to whip your butt into shape? Take step aerobics with SPRI's new slanted risers ($59.95, spri.com), which amp up the step's angle to 17 percent.