Here are five exercises to cut your gut and stack your pack.
Primary Muscles Worked: Rectus abdominus (your six-pack), the obliques, serratus, and the tranversus abdominus. This exercise also works your chest, shoulders, back, and even your glutes.
Why I Like It: This is a great exercise to strengthen your entire core. When done correctly it's taking the benefits of the plank and magnifying them. This exercise is great for building your serratus, which runs along the sides of your abs. When developed it really frames in your six-pack and makes you look extra fit.
How to: Start in a kneeling position. As the wheel rolls forward, you want to work toward a fully extended position. The more extended you are, the more challenging the exercise. Using your abs (not your arms) bring the wheel back to the starting position. Focus on a crunching motion, or "curling" your trunk. If you keep your back straight you will work more of your arms, lats, and shoulders. If you don't have access to an ab wheel you can use a straight bar with 10-pound plates on each side.
Primary Muscles Worked: Like the ab wheel, this works the abdominal muscles, the serratus, and obliques.
Why I Like It: Although this is still working the abdominus, I feel more emphasis on my obliques and serratus.
How to: In either a standing or kneeling position, grab a single handle for the cable machine, using an overhead pulley. Hold the handle to the side of your head, just slightly in front of you. Make sure to keep your elbow out in front of you. The more your arm is in front of you, the more you'll feel this working the serratus.
Primary Muscle Worked: The primary focus of this exercise is the abdominals.
Why I Like It: Although you can't isolate your upper abs from lower, I certainly feel that I'm able to emphasize the lower portion better with this exercise than I can with lying crunches.
How to: Although you can do this exercise from a roman chair, or from forearm straps, I prefer to do these hanging from a pullup bar. Hanging requires you to use more of your core to stabilize and keep your body from swinging. Keeping your knees together, raise your legs up until they are parallel with the floor. Do not use momentum to swing up. Crunch up in a controlled motion and pause at the top for an extra squeeze. Try to think of your trunk "crunching" to emphasize your abdominals. If you do these with your back straight, you will end up putting more emphasis on your hip flexors. If you want to make this exercise more challenging, do them with your legs straight, instead of bent.
Primary Muscle Worked: Like hanging leg raises, the primary purpose of this exercise is to isolate the abdominals.
Why I Like It: With the hanging leg raises I feel it more in my lower abs, but with this exercise I feel that it emphasizes more of my upper abs. Unlike regular crunches, by using the cable machine I'm able to add additional resistance. Abs are just like any other muscle and require resistance in order to develop. Doing 100s of reps is a waste of time. With resistance you can do 12-15 quality reps and really make the muscle work.
How to: In a kneeling position, hold the rope with both hands out in front of you. Keep your hands and arms in a fixed position, relative to your head and body. Now crunch downward, curling your trunk. Just like the other exercises, you aren't correctly targeting the abdominals if your back is straight. Make sure to squeeze at the bottom for a second and then slowly control it on the way back up. The "negative" is working the muscle as well.
Primary Muscle Worked: Just like the hanging leg raises and the cable crunches, you are focusing on your abdominals.
Why I Like It: With the hanging leg raises you are targeting the lower abs, and with the cable crunches you are focusing on the upper abs. With this exercise, the focus is on both.
How to: Lying on a bench, drop your legs off the end, with your feet on the floor. In this position, your abs are already slightly stretched. This helps me feel my lower abs when normally I wouldn't in a regular crunch. With your fingers placed lightly behind your head (in other words, do not yank your head forward) use your abs to curl up and forward. Make sure to squeeze at the top and then slowly lower yourself back down. To keep constant tension on the muscle, I never fully rest my head on the bench between reps. Again, make sure not to put your chin to your chest. That is just going to put stress on your neck. Keep a space there about the size of a fist.