Abdominal Anatomy
The low down on abs:
We all know our abs are important, but why? What’s the structure of our abdominals really like? What does each individual muscle contribute to their overall function? Here’s a bit of a breakdown on each muscle that makes up this group-where it starts and ends, and what it does…
Rectus abdominis
This is the muscle that runs vertically up and down our torso. It’s very close to the skin, and forms the famous “six-pack” look. The “dents” in the six pack are actually fibrous bands called tendinous inscriptions that run across the muscle. The rectus abdominis originates off the crest of the pubic bone and off of ligaments on the front of the pubic symphysis. It then inserts into the xiphoid process (that bit you don’t want to break off during CPR) and cartilage on the fifth to seventh ribs.
The rectus abdominis is responsible for spinal flexion, which can occur in three different ways. The most commonly thought of way to flex the spine is using a “crunch” type motion where the ribcage is brought down towards the pelvis. The opposite is also true however, the same muscles function to bring the pelvis up towards the ribcage in a leg and hip lift motion. The third option is that if neither the pelvis nor the ribcage are held still, the two can be brought together simultaneously…think crunching and lifting your legs and pelvis off the floor at the same time.
External obliques
These are the next deepest muscles, and the visible obliques on very lean individuals. They originate off the bottom 8 ribs and insert onto the linea alba (a fibrous structure that runs vertically down the middle of the torso) and the front half of the iliac crest (the bony bits that stick out from your waistband). The general direction of these muscles is in and down…draw an imaginary line from your left armpit to your belly button and you’ll get the idea.
The external obliques contribute to spinal flexion as well, or bringing the chest downward (they’re part of a “crunch” motion). They also play a roll in rotation, and compress the abdominal cavity (turning your torso and breathing out slowly and forcefully respectively). One side of the external obliques contracting by itself will result in a side bend.
Internal obliques
Much like the name suggests, these muscles are even deeper than the external obliques. They originate off the top half of the inguinal ligament (it runs in the crease between your thigh and your torso), the front 2/3 of the iliac crest (the bony bits that stick out from your waistband), and the thoracolumbar fascia (a saran-wrap like covering of the muscles of the mid and lower back that wrap around to the side of the body). They insert into the bottom 3 or 4 ribs and the linea alba (a fibrous structure that runs vertically down the middle of the torso). The general direction of these muscles is up and in…draw an imaginary line from your right hip to the right side of your sternum and you’ll get the idea.
The internal obliques often act in conjunction with your external obliques to rotate and side-bend the torso. For example, if you are doing a “twisting crunch” where you’re bending the torso and twisting to the left, your left internal and right external obliques are both contracting…wait, what? Let’s break it down. In this particular case, your right external obliques are essentially pulling your right armpit towards your belly button and your left internal obliques are essentially pulling your sternum towards your left hip. They’re both turning your body in the same direction. Because of their function in this situation, your internal obliques are sometimes called “same side rotators”. Internal obliques also act on your ribcage and breathing muscles, helping you breathe out forcefully (imagine you’re trying to blow out a bunch of birthday candles).
Transversus Abdominus (T.A)
This is the innermost and thinnest layer of the abdominal muscles. It originates off the inguinal ligament (it runs in the crease between your thigh and your torso), iliac crest (the bony bits that stick out from your waistband), thoracolumbar fascia (a saran-wrap like covering of the muscles of the mid and lower back that wrap around to the side of the body), and the lower 6 ribs. It inserts into the linea alba (a fibrous structure that runs vertically down the middle of the torso).
The T.A helps to compress the ribs and torso like a corset. This helps to provide stability to the torso and pelvis, but also visibly flattens the stomach. It is also an important part of the childbirth process.
