Originally posted by vat_man
Okay, lie down on your back, with your hands holding the back of your head and your legs stretched out.
Bring your knees up, so that your thights are pointing vertically, and your knees are bent at 90 degrees so your calves are horizontal with the floor.
Using your abs, left your upper back off the floor. Try to focus on pressing your lower back into the floor.
Now, touch your right elbow (keeping your hands behind your head) to your left knee. Your elbow and knee will have to move together to touch, with the opposite elbow and knee moving apart. Then repeat for the other side - you should then get a flowing motion where your legs make this bicycle pedalling motion as you straighten and draw up each knee.
Probably not the best description, but that's what you get. Good luck.