Planks work all the muscles in your core, including the back and pelvic muscles. When these muscles are strong, everything works better. You feel better, look better, and have more energy.
How to do it: Come into full plank position with your hands below your shoulders and your feet hip-width apart. Keeping your hips level and your core braced, lift your right leg and draw your right knee in toward your left elbow. (The knee does not have to touch elbow). Return your right foot to plank position and repeat on the other side, lifting your left knee in toward your right elbow. Continue alternating legs for 30 seconds.