The key to this exercise is to keep your back and hips absolutely still. The legs are simply levers creating more resistance for your abdominal muscles.
1. Lie on your back with your neck and arms relaxed.
2. Bend one knee so the foot is on the floor and raise the other straight leg up toward the ceiling.
3. Don’t let your hips and back move. At all.
4. Lower the raised leg toward the floor, but stop before your hips shift or your heel reaches the floor, whichever comes first.
5. Raise the leg without tilting or shifting your pelvis or low back.
6. Keep breathing and repeat.
1. Lie on your back with neck and arms relaxed. Breathe easily.
2. Raise both legs toward the ceiling.
3. Lower both straight legs toward the floor as far as you can without tilting, shifting or rotating your pelvis.
4. Raise and lower your legs as you breathe steadily.
5. Stop as soon as you cannot hold your stability.
For the therapeutic version, try the Easy Core Exercise in this article.