A quick list of low impact abdominal exercises.

1. Lying Bicycle: Sit on the floor, and prop your back at a 45 degree angle with the floor by using your hands. Bend your back so your abs can tighten better. Hold your legs up off the floor, and start bicycling on an imaginary bike. Repeat until exhaustion.
2. Ab Crunches: Sit down on the floor, and prop yourself up with your hands. Keep your knees bent at 45 degree angles and your feet planted on the floor. Tighten your abdominal muscles, and lower your upper body toward the floor while keeping your hands in the air next to your body. Use your abdominal muscles to lower your body, but do not allow your upper back and shoulders to touch the floor. Hold for 1-3 seconds, then bring your body back up until your hands can touch your legs. Do not rest in this position. Once your body is up, begin to lower it again. Repeat until exhaustion.
3. Lying Leg Raises: Lie down on the floor, and rest your hands palms down next to your hips. Using your abdominal muscles, start to raise up both your legs off the floor. Keep the feet together, heel to heel. Raise them up until they make a 60 degree angle with the floor, or just before the point where you can hold them in the air without straining your abdominal muscles. Hold them there for 1-3 seconds, then lower them back down, but don’t let them hit the floor. Let them touch the floor ever so slightly, and lift them back up once again. Repeat until exhaustion.
4. Twisting Ab Crunches: These are fun to do and they work your obliques, which are the muscles underneath your “love handles”. Use the same movement as for the Ab Crunches (described above), but with the following changes: (1) Instead of keeping your hands in the air, cross them on your chest, and (2) Instead of raising your trunk up in a straight curve, twist your trunk in alternate movements so one of your elbows is in line with the opposite knee. In other words, as you come up, twist your body to the left so your right elbow (your arms are cross, remember?) can almost touch your left knee. Lower your body and straighten it at the same time, then come back up and twist it to the right so your left elbow can almost touch your right knee. Repeat until exhaustion.
5. Twisting Lying Bicycle: If you’re ready for a high intensity ab exercise, this is it. Combine the movements of the Twisting Ab Crunches and Lying Bicycle crunches into one. As you bicycle your legs, lift your trunk up and twist it so opposite elbows and knees touch. You can either cross your arms on your chest, or cross your fingers behind your head (but make sure you don’t pull on your neck!), and do this until exhaustion. When you’re done with this, you’ll be done with abs for the day, because you’ll be too tired to do any other exercises.