The muscles of the core (and why we focus on the transverse abdominis!).

Hi everyone!

Generally, when people think of the core, they think of doing sit-ups, and crunches, and building up a 6-pack.  All of that has to do with the first muscle I’m going to mention here: the rectus abdominis.  However, there is so much more to the core than that.

1) The rectus abdominis: The “6-pack” muscle; flexes the trunk.

The rectus abdominis is the most superficial muscle of all the core muscles, meaning it’s the closest to the surface of your body.  This is why, when it’s well developed, it gives you those “six-pack abs” everyone talks about.  This is because it’s the easiest muscle to actually see. 

 Rectus abdominis
photo credit: sv:Användare:Chrizz

The rectus abdominis muscle is engaged when you flex the spine, or, in plain English, bend forward at the waist.  This is the main muscle you’re using when you perform the traditional “crunch” exercise.

20 years ago, the rectus abdominis was really the main muscle people thought about when they thought about the core.  That’s why, when I did my mom’s Jane Fonda workout videos for fun as a kid (yes, really!) all of the exercises in the “abs” segment were crunches.

However, we’ve learned a lot more about the core since then, and in particular, the role of the transverse abdominis in stabilizing the spine.  That’s why now, if you go to physical therapy or even to a personal trainer, they probably won’t place the same emphasis on crunches that they used to.  

(Of course, this is nothing against Jane Fonda– I have nothing but respect for her! She was totally ahead of her time, and totally paved the way for women in fitness!).

2) The obliques (internal and external): side bending and rotation.

The term “oblique” sort of refers to the fact that these muscles are off to the side, and off to a bit of an angle.

Unlike the rectus abdominis, which runs straight up the center of the abdomen, the obliques are located off to the sides of the abdomen.

As the names suggest, the internal obliques run underneath the rib cage, while the external obliques run above it, closer to the surface of the body.


Because they are off to the side, the obliques can perform motions that involve bending to the side, or rotating through the trunk.

This is why, in my Jane Fonda videos, she would talk about the obliques while doing the sort of crunch that would involve bringing one knee towards the shoulder on the opposite side.  It’s not a full rotation through the trunk (and with the SI joints, I really don’t recommend any exercises that do involve turning or twisting!).

Luckily, the obliques can be engaged with more subtle movements that don’t require you to do anything extreme, to fully turn or rotate through the trunk.  (More on specific exercises later!).

3) Transverse abdominis: stabilizes the spine and pelvis, including the SI joints.

The transverse abdominis is the deepest of all the muscles of the core.  It’s also the one we tend to be the least aware of, because we can’t see it.  It doesn’t give us a visible “six-pack” when it is strong.

However, the TA is arguably the most important muscle of all to strengthen, in order to stabilize the SI joints.  Studies have shown that, when it’s contracted, it directly reduces the amount of force that travels across the SI joints during movement (more on that later).

Here is a picture of the TA, just so you get an idea.  I think it literally does look like a corset.  When you contract it, it’s like you’re tightening the laces of that corset, stiffening the torso and the spine:

Transversus_abdominis (1).png

So how do we train the abdominal muscles to reduce back pain?  

Many people, myself included, believe the TA is the most important muscle to focus on, in terms of stabilizing the core.  However, the end goal is to have all of the abdominal muscles working together efficiently when we need them.

So how do we do this?

Luckily, all of the muscles above do play a role in supporting the trunk in the way the transverse abdominis does.  So, when we begin to train the TA, we are also switching on the rectus abdominis and the obliques.

And it’s this motion of TA activation — “compressing” the abdomen, as if you’re trying to withdraw your belly button in towards your spine) that really stabilizes the spine and pelvis.  This isn’t to say it isn’t important to also be strong in the other motions (the “crunch” motion, or turning motions).

But when you’re just starting out, it’s this “compressing” motion that’s really going to play the greatest role in reducing pain, and getting you up and moving again.

For me personally:

In my own recovery, I learned to activate the TA on land, in physical therapy. Then found it came very naturally to me to activate it while I was in the pool.  My lower back would actually start to hurt when I had bad posture or was arching my back, and I’d immediately remember “oh!  Contract the TA!”  And the pain would be gone.  For me, it very directly demonstrated the function of the TA.

However, as I progressed through my aquatic exercises, I did start to do maneuvers that involved the other motions (the “crunch” motion and movements that engaged the obliques in a sideways manner).   

With that being said, it is completely possible to strengthen the TA and make progress on land– more info on all of my exercises coming up!

When it comes to core strength, there is so much you can do!

What did you guys think of this post? Had you already heard of the transverse abdominis, or is this the first time you’d heard of it?

Let me know in the comments below!

Published by Christy Collins

Hi, I'm Christy! I'm a health coach who helps people overcome SI joint dysfunction and chronic pain.

4 thoughts on “The muscles of the core (and why we focus on the transverse abdominis!).

  1. So glad I found your blogs. I started with my third physiotherapist today. Have had SI joint dysfunction for a year now. This new physio is the first one who mentioned the TA muscle and I’ve been trying to remember to do it since I read about it on your blog. Looking forward to your e-book.


    1. Hi Ann, so glad my blogs have been helpful! The TA can be such a powerful tool when you know how to use it, so I’m really glad this physio is working on it with you! And thanks for saying that about my e-book– hoping to have it out soon. 🙂


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