There are four muscles that make up the anterior abdominal wall and four muscles that make up the posterior abdominal wall.

• The Rectus Abdominus

• The External Obliques

• The Internal Obliques

• The Transversus Abdominus

The Rectus Abdominus muscles go straight down the abdomen and rectus has a meaning of “straight”. They attach to the ribs and pelvis and act to pull the body forward. There are tendons which are attached at intersections which add to the leverage. The Rectus Abdominus  functions to keep the spine and pelvis stable as it works with other core muscles.

The External Obliques are locate on the sides of your body, just under the skin. They begin on the back of the lower ribs and run on a diagonal down toward the pelvis. These muscles are at work hardest when you twist or bend. They pull the spine forward just like the Rectus Abdominus, but because of their diagonal angle they also help to rotate and twist the spine. They also help to bend the waist and spine to the sides. If you are really lean, you can see these muscles because they are just under the skin.

The Internal Obliques and Transversus Abdominus muscles lie under them and cannot be seen for this reason.  The Internal Obliques rest just underneath of the External Obliques and they start at the pelvis, running upward toward the ribs on a diagonal line. They have multiple functions since they are deeper and closer to the spine. They help pull the spine forward and they stabilize both the pelvis and the spine during movement. The Transversus Abdominus is the deepest of the four anterior abdominal wall muscles. It plays a major part in stabilizing the lower back. It neither allows the spine to move forward, like in a crunch, nor does it allow the spine to twist or bend. The only function of the Transversus Abdominus is to stabilize the lower back. It does this by contracting before the arms and legs ever move. You cannot see it because it lies below the obliques. It is the first muscle to be activated during movements.

Anatomy Posterior Abdominal Wall:

• The Iliacus

• The Psoas Major

• The Quadratus Lumborum

• The Psoas Minor

The Iliacus is a muscle that attaches to the inside of the pelvis to the thigh bone (femur). Its’ main contribution to movement is to bend the hip (referred to as hip flexion), and it is one of the main  hip flexors.

The Psoas Major is a muscle that attaches all the lumbar vertebrae to the femur. The Psoas Major and Iliacus join with each other as they attach to the femur, so they are often referred to as one muscle, the Iliopsoas. Together they are the strongest hip flexor in the body. Since they are attached to the lower back and pelvis they can affect the position of the pelvis and the lower back during abdominal exercises.

The Quadratus Lumborum (QL) attaches to the pelvis, lower rib, and lumbar vertebrae. it is located toward the side of your lower back. It contributes as a core muscle to stabilize the pelvis, to allow the side to bend at the trunk, and to extend the lower back.

The Psoas Minor is considered to be a vestigial muscle which means not everyone has one. Even people who do have one may only have one not two. When present it is attached to the top lumbar vertebrae and extends to the pelvis. The contribution of this muscle is minimal in providing core stability or in allowing movement.