Crunches are a great way to tone your abs, especially when combined with diet and aerobic exercise. Add these crunches to your workout for flat, lean, rippling abs.

Basic crunches are the crunches that probably leap immediately to mind when someone mentions ab toning exercises. Basic crunches work on the rectus abdominus, the muscles that, when toned, give your abdomen that "six pack" appearance.

Perform basic crunches by lying on the floor. Bend your knees and place your feet flat on the floor. Bend your elbows and put your hands behind your head, or place your fingertips over your ears.

Lift your shoulders off the ground by contracting your abdominal muscles. You shouldn't sit all the way up, but should lift your shoulders only until your abdominal muscles are fully contracted. You can squeeze your abdominal muscle tight for a few seconds before lowering yourself slowly back down to the floor. Start out with 10 to 15 basic crunches, increasing your number of repetitions as your muscles gain strength.

Reverse crunches work on the muscles of the lower abdomen. They're a great compliment to basic crunches, since they tone your abs from the bottom up, while basic crunches work to tone them from the bottom down.

To perform a reverse crunch assume the basic crunch position, but lift your legs into the air. You can lower your arms to the floor, alongside your torso, for help with balance.

Squeeze your lower abdomen to lift your extended legs straight up into the air. Your pelvis should leave the floor, but the rest of your back should remain firmly flattened against the floor. You can squeeze your lower abdominal muscle as tight as you can for a few seconds with each crunch. Perform 10 to 15 reverse crunches to start, and increase your repetitions as your muscles gain strength.

Bicycle crunches work on the obliques, the muscles along the sides of your abdomen. To perform bicycle crunches, lie flat on your back, on the floor. Lift up your legs, keeping your knees bent so that your lower legs are at a 90 degree angle to the floor. Place your hands on either side of your head, or behind your head, with your elbows extended to the sides.

Perform a bicycle crunch by lifting your shoulders off the floor, the same way you do in a regular crunch. This time, you're going to bring one knee in toward your chest, and twist toward it with your opposite shoulder. Extend the other leg straight out into the air, so that your legs move as if you were rising a bicycle. Perform this motion on the other side to complete your bicycle crunch.

Bicycle crunches are one of the most effective ab toning exercises you can do. Perform 10 to 15 of them to start, increasing your repetition as your muscles gain strength.