Lie flat on the floor with your lower back pressed to the ground (pull your abs down to also target your deep abs). Interlace your fingers, and put your hands behind your head.
Bring your knees in toward your chest, and lift your shoulder blades off the ground.
Straighten your right leg out to about a 45-degree angle to the ground while turning your upper body to the left, bringing your right elbow toward the left knee. Make sure your rib cage is moving and not just your elbows.
Now switch sides and do the same motion on the other side to complete one rep (and to create the pedaling motion). Do this exercise with slow and controlled motion.