The Ab Muscle Group

Abdominal Muscles
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The Ab Muscle Group

Abdominal muscles are key for back support.  But did you know you have 6  of them?  There are 4 layers of abs in the ab muscle group; two of them - the external obliques and the internal obliques - each consist of two muscles (one on either side,) for a total of 6.

The abdominal muscles extend from various places on the ribs to various places on the pelvis. They provide movement and support to the trunk, an area known to many as the core.

 They also assist in the breathing process.

Every abdominal muscle plays its own role in spinal support.  This article presents the 4 layers and describes how they affect your posture and back health.

Why Abdominal Muscles are Special

Abdominal muscles are special because, along with other functions, they provide postural support. They also play a role defining your form. For example,the rectus abdominal muscle, which is the most superficial of all the abs, often yields a 6-pack effect when it is worked to a high degree of fitness.

More structurally, the deeper and closer to the spine the particular abdominal muscle is, the more effect over body posture it will likely exert, and this often contributes significantly to a healthy back.

The 6 Abdominal Muscles by Name

From deep (meaning the ab that is closest to the spine) to superficial (i.e., the ab that is furthest from the spine) the abdominal muscles are:

Note: Technically, the rectus abdominus is covered by the thin sheaths of the other abdominal muscles, but functionally it is furthest from the spine.

Let's take each layer, one at a time.

Deepest Ab Muscle - The Transverse Abdominal

The transverse abdominus muscle is the deepest ab muscle layer.

 Because of this It can have a significant effect on body posture. You cannot touch this muscle from the outside, but it wraps around the torso, creating an effect similar to a back support belt.

The Internal Oblique Muscles Exert a Strong Effect On Posture

The internal obliques are a pair of ab muscles - one on each side of the torso. They are just above to the transversus ab layer.  Like the transversus, the internal obliques significantly affect body posture, but a little less due to their slightly more superficial position. The internal obliques are involved in, among other things, rotation and lateral flexion of the spine.

External Oblique Ab Muscles

The external obliques are another pair of ab muscles located on either side of the torso. The external obliques are more superficial than the transversus and the internal obliques. Consequently they exert less effect (but certainly not none) on body posture. Like the internal obliques, the external obliques are involved in, among other things, rotation and lateral flexion of the spine.

Rectus Abdominus Muscle

As you can understand from the above, the order of ab muscles from deep to superficial is: Transversus, then internal oblique, and on top, the external oblique.  

The rectus abdominus, which at first glance seems like the most superficial of all the abs, is actually encased in the aponeurosis (broad sheet of connective tissue) of the internal oblique muscles.  But this encasement only occurs above an area known as the arcuate line.  (The arcuate line represents a discontinuation of a sheath of connective tissue located just deep to the rectus muscle.)

Below the arcuate line, the rectus abominus is located under all other aponeuroses, which makes it the deepest ab!

Regardless of its anatomical complexity, the rectus abdominus muscle is responsible for forward flexion of the spine, i.e. bending your forward, or rounding your trunk over. 

When contracting coencentrically, the abs, particularly the rectus abdominus oppose the action of the back muscles. What this means is that when the abdominals shorten to flex the spine, the back muscles are put on a stretch, and vice versa.

The Abs and Breathing:

The abdominals participate in the breathing process, especially during exhale, when they help force air out of the lungs by depressing the thorax.


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