Shorty Swan here to introduce all your abdominal muscles!
Let's work from the outside in or the most superficial muscles to the deepest.
Rectus Abdominus- Your 6 pack.
"Rectus abdominis". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons http://commons.wikimedia.org/wiki/File:Rectus_abdomin is.png#mediaviewer/File:Rectus_abdominis.png
The Rectus Abdominis start at your pubic symphysis and pubic crest, attaches to the cartilage of the 5th, 6th and 7th ribs and xiphoid process. It's two halves are connected by a band of thick connective tissue called the linea alba. More tendinous intersections transverse across each strip of vertically running muscle fibers, creating the segments of the sought-after six pack. It is your most superficial abdominal muscle.
What does it do?
The rectus causes flexion of the trunk by pulling your sternum and your pubic bone forward toward one another. It also aids in forceful respiration. In the studio you use it for your C curve, chest curl and pelvic tuck -- just to name a few!
External Obliques and Internal Obliques
The External Obliques are the next layer below the rectus, while still being the most superficial muscle of the side body. The external obliques start along the outer surfaces of the lower 8 ribs where they interlace with the serratus anterior. They run on a diagonal, forward and in, towards the midline of your body, where they insert at the pubis, anterior (front) iliac crest, ilioinguinal ligament and linea alba. The fibers of external obliques run in the same diagonal direction. The muscle fibers run in the direction your fingers point when you place your hands like you were preparing to reach into your pants pockets.
What do they do?
When both the right and left external oblique flex at the same time or bilaterally they flex the trunk, bringing your rib cage towards your pelvis when you hold your pelvis still or vice versus. When one side is working on its own, it cause either side bending or rotation of the trunk towards the opposite side. For example, your right external oblique side bends you to the right and turns you to the left. If you visualize the direction of the muscle fibers, this makes perfect sense. In the studio you use these in criss cross, mermaid, saw, snake and twist and global stabilization of the spine.
The internal obliques are underneath or deep to the external obliques and they run in the opposite diagonal. These deep abdominals originate at the inguinal ligament, anterior iliac crest and deep layer of fascia in the low back called the lumbodorsal fascia. (Think lumbo like lumbar spine and dorsal means backside). From there they run up and in to insert at low ribs 9 through 12. The internal oblique fibers directionally make an X with the external oblique fibers. If you cross your arms over your torso and let your fingers land at the top of your iliac crests, the internal oblique fibers run in the same direction as your fingers.
What do they do?
When flexed bilaterally the internal obliques compress your abdominal contents and help flex your torso forward. When flexed unilaterally, they facilitate side bending and rotation to the same side of the trunk. For example if you side bend to the left you are using both your internal and external obliques on the left side. If you rotate your rib cage to the left (but leave your pelvis facing forward) you engage your internal obliques on the left and your external obliques on the right.
Transverse Abdominus - Your functional corset.
This is the deepest layer of your abdominals, closest to your organs and your center line. The fibers of the transverse abdominis run crosswise like a belt around your torso. Understanding the direction of the fibers helps us visual where it attaches, all around the bones of our center not just in the front. The transverse originates from the inguinal ligament, along the iliac crests in the front body and wraps around, anchoring in the back to the same lumbodorsal fascia as the internal oblique, the lumbar vertebrae and the inside surface of the bottom seven ribs!! In these back attachments it interlaces with the diaphragm. So the origins are really covering a lot of surface from top to bottom in your torso! All these fibers belt around to attach into the linea alba, the same midline marker that splits your six pack!
What does it do?
When the transverse fires it tightens like a corset decreasing the circumference of the torso. This contraction causes compression of the contents of our abdominal cavity. In short, it pulls the belly in 360 degrees towards center. It also fires when you cough or laugh. The transverse, like all the abdominal muscles, helps to stabilize the spine
Here is a great image that allows you to see each layer, but all the layers in relation to each other.
These abdominal muscles partner with the musculature of your back, pelvis, your pelvic floor and your diaphragm to encapsulate your organs. All together they are your core, your powerhouse, your center! We identify them separately, like identifying the members of a band, but they work in concert with each other. They are a functional family of support and strength for your body.
Check out Explore Your Core for movements to activate all of these muscles. Or get outside and MOVE!