This exercise is more difficult than it looks. I have found that it is great for people with a large anterior pelvic tilt and large lordotic curve. It forces them to learn to use their abdominal muscles correctly in stabilizing the pelvis.
Lying flat on your back, start with your hands behind your head and your shoulders off the ground (so you are in a slightly crunched position to start). Knees should be bent at 90 degrees. Slowly extend one leg out, making sure to keep your lower back as flat on the ground as possible.
Bring your leg back in to 90 degrees and repeat on the other leg. Continue alternating legs until you reach 10 reps on each leg. Remember to keep shoulders off the ground the entire time.
