Before I talk about one of the most productive and forgotten Ab Development exercises ever developed, you will need to know how your abdominal muscles actually work. I know for a fact, if I don't offer some pretty convincing evidence, it will be very difficult for you to believe such a claim so here is where a little education will go a long way to prove my point.
Your abdominal muscles are really one big muscle called the Rectus Abdominus. You do not have upper, mid and lower abs unless you have some genetic anomaly. This is really critical to understand because the long muscle fibers in the abdominal muscles start at ribcage and ends at the pubic region.
So, when you contract your muscles during a curl-up or crunch, the two ends of the muscle fibers move toward each other. It is impossible for the lower portion of the Rectus Abdominus (abs) to function without equally "firing off" all the other muscle fibers in the abs.
Once the muscle relaxes and allows its two ends to move apart and reach its original stretched position, you will complete the full range-of-motion of an abdominal exercise,
I am not forgetting the external and internal Obliques because they are directly and indirectly involved while performing any abdominal movement so it's really not necessary to hammer out your Obliques regularly. In fact, since the only thing a muscle can do is shrink and grow (atrophy or hypertrophy), you probably will not want to overly develop the Obliques because it will create a thicker looking waistline.
That means the key to creating great-developed abs is to use exercises that fully contract the abdominal muscle until it is fatigued and that will take the muscle through it's full range-of-motion, just like any other muscle you build in your body.
Remember though, you will not see your abs if they are hidden under a layer of fat and you cannot spot reduce the fat from waistline by training your abs for hours on end. Simply doing hours of abdominal exercises may develop your abs but you will still carry that layer of fat around your body if you aren't burning the appropriate amount of calories. If you are trying to lose body fat, there are much bigger and better exercises than abdominal exercises for burning calories and body fat.
Now that you know how the abdominal muscle works, it's time to discover, "The most forgotten productive exercise for your Abs."
Reintroducing, TADA - The Sit Up.
Wait! Don't go yet. It's really, really important for you to know how to properly perform a Sit Up. If you perform the Sit Up like you did in Gym Class, you are reducing the Sit Up's effectiveness by almost 50% and you could cause some serious low back pain for yourself.
I know; if a personal trainer or non free-thinking exercise physiologist is reading this section right now they are going to tell me I am crazy for recommending Sit Ups. Here again, it is important to understand the rules behind Abdominal-development and the Sit Up exercise really qualifies as a very effective movement.
Remember, when the abdominal muscle is working, "Two ends of the muscle fibers must move toward each other and be able to fully contract".
Does the Sternum and Pubic area move toward each other when performing Sit Ups?
Does the Abdominal Muscle bend and stretch the spine in its full range of motion in a Sit Up?
Does the abdominal muscles reach full extension to full flexion?- YES, if you perform the exercise correctly! So, why does the sit up exercise get such a bad rap?
Primarily because the old style Sit Ups you performed incorrectly in gym class put too much stress on the lower back and hip flexors. But, do you know what is really crazy about that logic? If more muscles than one are involved, it is called a compound or multi-joint movement. You won't hear me saying compound movements are bad. Are these supposed experts trying to get people to actually believe that compound movements are great for every muscle except the abdominal muscles?
If I remember correctly, didn't these same exercise physiologists claim squats and Deadlifts put too much strain on your knees and back and that we all needed to stop doing those exercises too? Just a few years later, most of the experts are now eating their words, aren't they?
Description of Exercise - Here is the appropriate way to perform an effective Sit Up.
Lay flat on your back with a rolled up towel under your lower back. Bend your knees about 45° with heels on the floor and keep your toes pointing up. Do not anchor your feet.
Spread the knees apart approximately 6-8 inches to prevent the hip flexors from contributing too much to the exercise.
Next, extend your arms between your legs and keep your hands between your legs throughout the movement because it will help keep you in the proper position.
Now, exhale and lift your shoulders off the ground, keeping your neck in a neutral position. Concentrate on trying to force the lower portion of your ribcage into your knees by curling the spine upward into the sit up position. (DO NOT CURL YOUR NECK). Slowly lower yourself back down to the starting position by uncurling your spine and you are finished with the repetition when you feel the rolled up towel supporting your lower back again.
Notice how both ends of the abdominal muscle fully contract together and are stretched through its full range of motion. When you perform a Sit Up with proper biomechanics, your next crunch exercise will pale by comparison.