Bicycle crunches consist of lying flat on your back, your hand on the back of your head, knees bent to face the ceiling, feet flat on the floor. To perform the bicycle crunch bring one elbow up toward your opposite knee as you bring the knee toward your elbow. This will cause you to move part of your upper body and you should feel the workout in your abs. As you progressively get better at this move you can bring your legs straight up in to the air. 5 minutes of this 3 times a week should be an adequate amount of time. It is important during this exercise to keep your abs drawn in to your spine.