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The Abdominal Wall

I’m going to be talking about the abdomen for the entire month of November – we will chat about the muscular anatomy and function, diastasis recti, pressure regulation/breathing, scar tissue and the viscera that lies within!

But first, I want to lay the groundwork. So we are going to delve into the muscular anatomy of the abdomen so that you can understand how each layer works.

The abdominal wall muscle tissue has a variety of different functions: it stabilizes our pelvis and lumbar spine to help us maintain appropriate upright posture, it can flex and rotate the trunk and it also has a huge role in regulating the pressure within our abdominal cavity.

There are four different muscles that form our abdominal wall: Rectus abdominis, external oblique, internal oblique and transverse abdominis. Read on to learn a bit more about each of their individual anatomy and function:

  • Rectus abdominis
    • This is the muscle that most of us think of when we think of “abs.” That six-pack muscle is your rectus abdominis. It’s essentially a long band of muscle that runs from our pubis all the way up to our 5th, 6th and 7th ribs and the xiphoid process (the bottom part of our sternum). The muscle is separated at midline by a line of connective tissue called the linea alba. This is the area that separates when someone develops a diastasis rectus abdominis or diastasis recti. That “six-pack” effect is caused by fibrous bands that run across the muscle (there are 6 of these bands total, so when someone is particularly lean or well-developed through this muscle, and “eight-pack” effect can be seen. The rectus abdominis runs between the ribs and the pubic bone, so when it contracts it brings those two points together. This results in a “crunch” type motion. If the ribcage is fixed, it will bring the pubic bone up toward the ribs, thereby creating a posterior pelvic tilt. The rectus abdominis is NOT what we should be targeting when we’re thinking about functional “core” strength – this muscle ONLY serves to flex the trunk, which is not particularly functional.
  • External oblique
    • These muscles lie superficially on the sides of our abdomen. They begin on our lower eight ribs and run downward toward our iliac crests (the bony portion of our pelvis), the pubic bone and linea alba (at midline). Each side of the external oblique can act independently, or they can act together. If one side contracts on its own, it will side bend the trunk toward the contracting side and rotate the trunk away from the contracting side. For example, the left external oblique will bend your trunk to the left and rotate it toward the right. Try it this movement and feel your lower abdomen on the left – the contraction of the external oblique is obvious!  If both sides contract together the pubic bone is drawn up toward the sternum, thereby flexing the spine slightly or causing a posterior pelvic tilt.
  • Internal oblique
    • These muscles run perpendicular the thicker and more superficial external oblique. They originate on our thoracolumbar fascia in our back as well as the iliac crests of our pelvis and run forward and upward toward the lower three ribs, xiphoid process and linea alba. The internal oblique is similar to the external oblique in that it can contract one side, or both sides can contract together. One-sided internal oblique contractions will side bend and rotate the trunk toward the contracting side (that is, left internal oblique contraction will rotate and side bend the trunk to the right). If both sides contract together, it can increase intra-abdominal pressure as it narrows the abdominal cavity. People often compensate for transverse abdominis by using their internal oblique!
  • Transverse abdominis (“TA”)
    • This is our deepest and thinnest abdominal muscle. It starts on our back, with attachments on our lower six ribs and lumbar fascia and wraps around toward the front of the abdomen, where it attaches along the xiphoid process, linea alba and pubis. This is truly the muscle that forms our deep abdominal wall that holds our viscera within. When this muscle contracts, it acts like a corset or drawstring and narrows the abdomen. This is the muscle that is truly responsible for stabilizing our lumbar spine and pelvic girdle. It’s also the muscle that tends to be weak in most people!

Why does the transverse abdominis get weak? Well, we often don’t focus on isolating or activating our TA, so we lose coordination in that area. And then we get really, really good at compensating, so we learn to use our other muscles (especially internal obliques, hip flexors and pelvic floor). Think about it: our body is smart and it’s going to recruit whatever muscles it needs to get things done. So, if TA isn’t firing appropriately, well, you can bet that something else is going to step in and try to compensate. But here’s the problem – those compensations ultimately will lead to problems somewhere else. For example, tight hip flexors can change the position and mechanics of your lumbar spine, and you may end up with back pain. Similarly, the pelvic floor can get overworked and hypertonic in an attempt to regulate the pressure in your abdomen.

So how do we activate the TA? I’m glad you asked! I like to instruct people to do this in two positions.

  • Let’s first start by lying on your back with your knees bent and feet flat on the floor. Your spine should be in a neutral position (your pelvis is on the ground, but your back should have a very slight arch). Take a deep breath in and feel your abdomen expand. As you exhale, think of blowing through a straw and draw your navel toward your spine. Your abdomen should narrow, but your low back should NOT move! If your back presses into the ground, you’ve overdone it and used your obliques and/or rectus abdominis!
  • Another great way to learn to activate your transverse abdominis is in sitting. Sit in a chair with your back off of the back rest and plant your feet flat on the ground. Think of taking the pressure off of our waistband gently as you exhale. Nothing should have moved as you contracted your TA.
  • Note: Check my Instagram and Facebook for videos on how to do this!

As you can see, TA activation is subtle, but SO important! And here’s the good news: the TA is activated with all weight-bearing movement, so simply getting moving when you’re recovering from an injury walking can be a great way to initiate core strengthening!

Join me in the coming weeks when we discuss how to regulate the pressure in our abdomen (and what that means for the pelvic floor), diastasis rectus abdominis, hernias, as well as abdominal surgery and its implications for the viscera!

What questions do you have about the abdomen and its anatomy? Leave them below!

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