Planks [1] are one of the best exercises you can do if you're looking to strengthen and sculpt your midsection. If you've already mastered the elbow plank [2] and the side plank [3], try this variation to really fire up your abs. Here's how to do it:

• Start face down on the floor resting on your forearms and knees.
• Push off the floor, raising up off your knees onto your toes and resting mainly on your elbows.
• Contract your abdominals to keep yourself up and prevent your booty from sticking up.
• Keep your back flat — don't let it droop or you'll be defeating the purpose. Picture your body as a long straight board, or plank.
• With a flat back, use your elbows you pull your body forward, then come back to your starting position. Be sure to keep your neck and spine in a neutral position. This completes one rep.
• Do 12 reps, rest for 30-60 seconds, and complete two more sets.