Plank

Targeted Muscles: transverse abdominus Set up: Start facedown on a mat. Press up onto your forearms and toes, keeping your elbows under your shoulders and your body straight. Action: Hold this position for as long as your can; aim for 30 seconds at first, working up to 90 seconds. Watch that your hips don't drop and your shoulders don't creep up toward your ears. Oxygen Magazine