If you're are short on time, but want to get a solid ab workout in this is for you!
50 continuous leg lifts
50 continuous Russian twists
50 concentrated situps
Make the alphabet with your legs 2 sets (DON'T LET YOUR LEGS TOUCH THE GROUND!)
Your abs will burn and you will feel it in your lower core. This is a quick and easy way to get definition on your lower stomach.