In order to do this exercise, you’ll need to start by lying down on your back. Be sure that your arms are placed by your side and that they are facing forward. Next, you’ll need to keep your knees straight while raising your legs to about a 90-degree angle. Now, tighten you abdominal muscles. As you do this, lift your hips up off of the ground by a few inches. Hold this position for a few seconds and then rest. Continue this process until you get tired.