Killer Move: Ab and Back Toner

Even a ton of crunches won't give you strong, flat abs if your core is weak, says Lashaun Dale, group fitness creative manager at Equinox Fitness Clubs in New York City. This two-part move hits your deep abs, "six-pack," obliques, and lower back. Work up to three sets.

a. Lie on your back with legs extended and arms at sides. Using your ab muscles, roll up to a seated position, bending left knee while lifting right leg 3 inches off the floor; extend right arm above you, close to your right ear.

b. Keeping right arm and leg lifted, roll back down and turn to your left, straightening left leg to roll over onto your belly and moving left hand out to side. With right arm still extended and left palm pressing into floor, lift both legs for a back extension. Push off your left palm to roll back to the starting position. Repeat for a total of 8 to 10 times; switch legs.

Originally published in FITNESS magazine, September 2006.