You can do regular crunches all day long, but that gets pretty boring for you and your abs. Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise. Six-pack, here you come!
* Lie flat on the floor with your lower back pressed to the ground (pull your navel in to also target your deep abs).
* Put your hands behind your head, then bring your knees in towards your chest and lift your shoulder blades off the ground, but be sure not to pull on your neck.
* 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 towards 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.
* Do three sets of 20 reps
Speed is not the name of the game here; go slowly to focus on your form and your breathing. Also, it is not necessary to touch your elbows to your knees as this could cause strain in your neck.
Source Pop Sugar