Core Ab Exercise - Single Leg Stretch/ Bicycle

This core ab exercise requires a lot more control than people think. When you do it correctly it's freakin' hard!
Make sure you keep your lower back pressing into the floor THE ENTIRE TIME.
Keep even weight in both your hips, even as you add rotation in the upper body. Make the rotation come from the space between your ribcage and the top of you hips - everything else stays the same.
Keep your elbows so wide that you can't see them out of the corners of your eyes. Keep your chest open.