Scissors Exercise is a great lower ab strengthener. Again Angular Training plays into effect here in order to fatigue your lower abs most effectively.
How to do the Scissors Exercise:
Lay on the ground with your hands under your buttocks. This is to help support your low back. Lift your legs up about 3-4 inches off the ground. Bring them all the way out toward opposite walls, then bring them together and cross them over each other. Bring them out again and cross them over each other making sure each leg gets a turn being on top.
Muscle group worked:
Target Repetitions for Muscle Growth: 6-8
Target Repetitions for Muscle Tone/Endurance: 8-12
Why the Scissors Exercise works:
Scissors Exercise works so well because of the plane you are moving your legs on. Since you have to cross your legs over each other they are moving on two different planes, not just one.
Make sure to keep your hands under your buttocks with the Scissors Exercise so that you do not injure your low back.
Breath slow and steadily throughout this exercise.
Disclaimer: Talk to your primary care physician before beginning any exercise regimen.