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