This section is not intended to replace a scientific anatomy text book. Here is a brief outline of the different areas of your core and how they are trained and some of the movements they produce.
Your core is made up of :
The Inner Unit
Your inner unit functions together to work as your bodies natural weight belt. The muscles should contract together and pull the pressure off of your spine. They also work to flatten your stomach. Training the inner unit is important for posture, supporting your spine, flattening your stomach, sports performance and avoiding injuries. Surprisingly, many core strengthening programs ignore training this area completely.
The rectus abdominis is one muscle but is fed by two different nerves and the two sections have slightly different movements. Your lower abs pull your pelvis towards the rib cage and your upper and pull your torso and rib cage toward your pelvis. Therefore to train both movements is important. The rectus abdominis also works as one unit in stabilization. Many ab training programs ignore the lower abs and stabilization function of the rectus abdominis.
Your obliques run from your rib cage to your pelvis and function in rotating your torso, side flexion and stabilization of the trunk.
Your erector spinae extends your spine and works to stabilize your trunk as well. It is imperative to train both flexion and extension of the trunk. Also, your spine needs isometric work to help with its stabilization function.