If you want your abs to be in great shape you of course have to work them. Crunches are a great way to work your abs, but that only works one muscle group. In order to work all the different groups, you have to make some changes to your crunches. For instance, while doing your crunches, lift your knees each time you raise your upper body. As you do this, bring your left elbow towards your right knee. Also, lie on your back and raise your legs, knees slightly bent, where they are perpendicular to the floor. Raise your pelvis as you work your lower abs. Another ab exercise is to pull your upper body with your elbows toward your knees as you raise them. Pull yourself into this "ball," then extend your legs but don't let them touch the floor. Repeat this movement and you will work both upper and lower abs.