When you think about killer abs, you probably picture a six-pack. But it's time to think broader – literally. To have the strongest and most cut-looking core, you have to train the obliques, the muscles that run along your sides. They help stabilize your body during any movement, particularly when you rotate your trunk, and they'll also cinch in your waist.

To get the fastest results, you want to hit them from multiple positions: face up, facedown, and standing.

1) Bicycle Crunches
Lie face up with your hands behind your head, legs extended and six inches off the floor. Crunch up and twist to the left to reach your right elbow to your left knee, slowly returning to start and repeating on the opposite side for 1 rep. Do 3 sets of 15 reps. Tip: Try to keep your legs as low as possible to the floor as you move, and turn your head in the direction you're rotating to get a deeper twist. 

2) Plank Transfers
Get into plank position on a mat with your forearms down, a set of four 5-pound weight plates stacked outside the top right corner of the mat. Keeping your back flat and butt down, pick up one plate with your left hand and put it down on the opposite side of the mat; continue to transfer the plates until all are stacked in the top left corner. Repeat, using your right hand to transfer and stack the plates, and continue for 1 minute. Here's how it's done. 

3) Standing Tilts
Stand with feet shoulder width apart and holding a 25-pound weight plate with both hands directly overhead. Slowly lean to your right side until you feel your left obliques engage; hold for 5 beats. Repeat on the opposite side for 1 rep. Do 3 sets of 10 reps. (Too easy? Try it with 15-pound dumbbells. The free weights will force your obliques to work harder to keep you stable.)