Although this move is a little more advanced, it will make your lower abs burn. Try to lift your upper body up off the floor as much as possible so your arms meet your knees.
Lie on your back, and reach your arms rigidly to your side, off the floor. Lift your legs off the floor and point them, so they are at about a 45-degree angle. Lift your head, so your shoulders are off the floor as well.
When you're ready to begin, lift your upper torso off the floor, and bend your knees. You can lean back to make this move harder or come up more to make it easier. Slowly lower your upper body back down to the floor, straightening out your legs as you do so. Stop when your back is on the floor, but not your head, shoulders, or legs.
This completes one rep. Do 10 to 12 reps per set, and do two to three sets.