"Doing crunches only works your upper abs. Real core fitness involves working your upper and lower abs, internal and external obliques, and back muscles...
Most people get down on the floor and do crunches and then wonder why their belly is still protruding. Doing crunches only works the section by your lower ribcage. In order to stregnthen the lower abs, lower abs exercises must be done.
For Real Core Fitness you must do exercises that target the upper and lower abs, internal and external obliques (lower front and side section of rib cage area) and back. Working all of these muscles with specific exercises will help you strengthen your core, which in turn creates a stronger foundation when exercising other muscle groups within the body.
Think of it this way....Your core is like the trunk of a tree. The tree must have a strong trunk in order to hold up the branches as well as get through strong winds, etc.
Activities that help work your core are stability ball, bosu, pilates, and of course, floor exercises for abs and back. A FUN new way to exercise your core is the new Bull Fitness class. This class involves riding a mechanical bull, like the one at Travaasa Austin. http://www.travaasa.com/
---from my book "Real Health Real Life."