Some walls are stronger than others. Try to break through a wall built with straw and you are met with very little resistance. Try to break through sticks and the effort required is greater. Encounter a wall built with layers of bricks and you will then realize that some walls are really stronger than others. Each layer bonded with the other layer adds more resistance and toughness; until a nearly impenetrable wall as wide as it is thick is created and built to last. The human body has a built-in wall that is built to last. This wall is also built in layers. Instead of bricks, this wall has layers of muscles. Each layer adds strength and flexibility. In fact, you could say this wall is strong enough to bend.
Each layer of the abdominal wall has a purpose. The Rectus Abdominis (RA) is a series of muscle bundles which account for large amounts of bending forwards and backwards.
A deeper layer called the External Oblique (EO) allows the body to bend laterally. The deepest layers of this muscular wall are called the Internal Oblique (IO) and the Transverse Abdominis (TA). Both provide the strongest amount of support. All of these layers combined provide support for the torso like a built-in corset. The abdominal contents are held in tightly and the body is kept from buckling against the gravitational forces that want nothing more than for things to fall to the floor.
Besides withstanding the effects of gravity, this multi-layered, multi-directional wall of muscles can withstand quite a bit of bending, twisting, pushing and pulling. All by design; depending on where the torso is in space determines which layer is more or less supportive at any given moment. Even a master brick layer could not have designed a better system.
However, even well built objects need to be maintained. Maintaining your built-in wall is up to you. If you focus on one specific exercise in one specific direction, you will throw the system out of balance. Most people focus on the RA and neglect the EO, IO, and TA. Big mistake All the layers are equally important for supporting the delicate internal organs, the spine and the pelvis. All the abdominal wall layers need to be included in an exercise program in order to maintain the strongest wall possible. When designing an abdominal strengthening routine, you must respect the multi-directional nature of this wall with exercises that challenge the muscle in many different directions. For example, the use of a wobble board will greatly enhance at traditional sit-up from a one dimensional exercise to an abdominal burning workout. Just lie on the wobble board in a belly-up, knees bent position and let 'er rip. Not only will you have a ripped "six pack" but you will also have a strong, built-in wall made to withstand the tests of time.
Time does take its toll on all walls; sticks, bricks and muscle all included. Obesity will weaken the abdominal wall with large guts that stretch the wall into a paper-thin nothingness, similar to the effects of pregnancy. Additionally, women can have the wall weakened by a surgeon's scalpel that cuts through to extract a baby or a uterus. Some walls just weaken from neglect. Do not let that happen to your abdominal wall. Keep it tight, keep it strong and your wall will be stronger than others.