• jaimieharrow

Your Core is a Cube, Not a Wall

Updated: Oct 22, 2018

We can lump the word ‘core’ in with other marketing buzzwords like ‘natural’ and ‘superfood’. They don’t mean anything specific and are utilized to sell ideas of health, strength, or safety. Many of us (hopefully) roll our eyes when we see words like ‘detox’ on a product label and more and more folks are feeling the same way when ‘core’ is added as a prefix to any number of other fitness activities.

Core Yoga!

Core Pilates!


Coopted largely by the marketing departments of agro sports businesses, ‘core’ has become synonymous with washboard abs, ostentatious obliques, and a focus on lumbar flexion movements that require anterior abdominal contraction. The image that is often associated with this common interpretation is a wall on the front side of your body composed of 90% rectus abdominis (that’s the 6-pack muscle) and 10% obliques. That’s about it. This is a misrepresentation of what true ‘core’ musculature is. Now, there's nothing wrong with wanting to work on your physique, but we should call it what it is and give the concept of the Core it's rightful attention.

Here’s why this matters:

The role of rectus abdominis is primarily to flex the lumbar spine – bringing our ribs and our pelvis closer together. One common back injury is a disc herniation, where the intervertebral disc between our vertebra migrates backwards into the canal where our spinal cord lives. Want to guess what spine position is most implicated in this injury? That’s right – lumbar flexion (with a dash of rotation). Bending forward can push the stuff between our vertebral bodies backwards and numerous studies by leading researchers have shown that repetitive flexion motions, especially under even small loads, can accelerate spine problems. So how do we reconcile the discrepancy that the core is often lauded at protecting our backs but the muscle primarily marketed as the King of Core performs the very motion that can lead to injury? Abdominal engagement is more complex than just lumbar flexion, and if we understand this we can be smarter about our own movement and training.

I would like to support a new image to associate with your core. Not a wall, but a cube made up of front, sides, back, top, and bottom. I will now break down what I see as vital components of each section. This is not an exhaustive list, but it should expand your awareness of just what is creating stability in our lower trunk.

The Front:

On the front we have our familiar rectus abdominis, the beach-body muscle that many strive for. But in addition we have the ‘little girdle that could’: transverse abdominis! This muscle, which wraps horizontally around our low abdomen, is highly associated with lumbar stabilization and has been used clinically to help reduce sacroiliac joint pain, lumbar pain, and more. You can think of it like a corset, it squeezes our abdomen, increasing intra-abdominal pressure (among other things, more on this concept later) when activated and preventing unwanted movement at our spinal joints which can contribute to pain. Training of this muscle is supported by the American Physical Therapy Association's clinical practice guidelines as well as numerous studies. It's good to know that there is debate about the role of this muscle - some studies counter that to get the benefit of this muscle's activation we don't need to do specific targeted exercises but can, instead, perform more general abdominal routines. The debate continues, but it's a good issue to know about.

The Sides:

There are three components of our sidewall I want to highlight. Two obvious components are the internal and external obliques. These tend to be familiar muscles to most so I won’t spend too much time here. Suffice it to say that while we often think of the obliques as movers – that is, they move us into rotation around our spine – the do just as much to RESIST movement and control motion. This ability to eccentrically control movement is crucial for spine health and stability – it lets us feel confident stopping motion before it goes too far.

The underdog I want to point out in our sidewall is the quadratus lumborum. This muscle is primarily a lateral flexor – it sidebends the trunk (and, as a result, also resists sidebend). It has connections, however, directly on the spine – the transverse processes of many lumbar vertebrae. Because it is both directly next to the spine but wide enough to have fibers far away from the spine, it works well as both a mover and a stabilizer. Also, due to its position and ability to step in for so many other muscles, the quadratus lumborum is often involved in complex compensation patterns. Since it can extend the spine it sometimes masquerades as the erectors or multifidi. Since it can lift the ilium it may step in for a malfunctioning gluteus medius (a common problem!). I find, clinically, that many acrobatic movers frequently have problems with this muscle due to it’s ability to cover for other non-performing muscles, so it’s worth being aware of.

The Back:

Lumbar Multifidi

In the back we have a number of muscles that help to produce movement around and stabilize the intervertebral joints. In the lumbar spine the biggest of these muscles close to the spine are the multifidi, but others exist in a complex array of small muscles ready to assist or resist certain motions. The largest muscles here, the ‘erectors’ (which is a term referring to a number of superficial muscles that make up the big lump of muscle on either side of your spinal column), have the unique property of crossing the sacroiliac joint on the posterior surface of the body. This joint is often a source of pain either due to a lack of movement or, often, too much movement which the brain can interpret as instability. Learning to engage the muscles that cross this joint on all sides can go a long way to preventing or helping low back pain. This study has identified the erectors (along with gluteus maximus and biceps femoris of your hamstring group) to be important in stabilizing this joint.

The Top:

At the top of our cube we have our diaphragm. This umbrella-shaped muscle flattens out when it contracts and draws air into our lungs. It provides the roof of our box and, when contracted along with other muscles, helps to build intra-abdominal pressure (discussion of this at the bottom). Many of us who have not focused on our breathing for a long time might find it difficult to access our diaphragm consciously. Working on ‘belly breathing’ can help to reconnect us with this essential muscle.

The Bottom:

The pelvic floor! This is an area most of us don’t consider when we think about our core. Your body has another muscular diaphragm opposite the breathing diaphragm – it sits in the bowl of your pelvis and is made up of a few muscles that support everything on top of them. These muscles are essential in pushing up against pressure so we can brace our abdominals and diaphragm and create some intra-abdominal pressure (notice a theme developing?). While these muscles can definitely be weak or low-tone and create problems, the opposite is also often true. These muscles are often over-worked as they compensate for other structures not doing their job. Alternatively, some athletes bring their intense core focus into their every day activities and keep contracting these muscles all the time without stopping. This results in excessive tightening and an ‘always-on’ tone which can lead to problems with urination, pain in our abdomen or genitalia, and more. Studies are now finding lots of correlation between low back pain and pelvic floor dysfunction as well, so it's worth being aware of. There are PT’s that specialize in pelvic floor work and if you have questions about this stuff it’s worth seeking out someone who really focuses on these areas.

So there we have it – the Core Cubed! This model pivots from the traditional unidirectional model of abdominal activation and brings it to youin 3D!!!

This cube concept is important because one of the main purposes of our core musculature is to allow us to stabilize the structures in the middle (such as our spinal column). Low back pain is an incredibly pervasive problem in our society and as we live longer and do more we demand greater and greater integrity from these carefully aligned joints. To do this effectively we need muscles on both sides in every plane: back and front, side and other side, top and bottom. This way while certain muscles move us the other side can control that movement. Our brain is confident about movement when it knows we have the ability to produce strength and control in all of the available range of motion. We are much less likely to have a movement fault or have our brain decide certain motions are threatening if we have worked on muscle activation of the whole package and not just our rectus abdominis.

"Our brain is confident about movement when it knows we have the ability to produce strength and control in all of the available range of motion."

Last Piece of The Puzzle

An additional piece of this puzzle is that when all of these muscles contract simultaneously we can build intra-abdominal pressure. This is similar to 'bearing down' while trying to defecate except we skip the last part. Not the most popular topic of conversation, this ability to create pressure inside our abdomen has been studied extensively and is linked to the ability to actually unload the spinal column from compressive forces. It makes sense if you think about it - if you keep putting air into a balloon it'll stretch apart and grow. The same appears to be true (on a much smaller scale) for your spine - the pressure literally pushes the segments apart slightly. This article offers in their conclusions that we don't fully understand how this happens yet and much more research is needed, but the correlation has been identified.

But here's the thing - without all six sides of the cube working together pressure can't be effectively built. It takes conscious activation of all parts to create the Cube.

In future articles I will show some various ways to work on all of these aspects of our core. I hope this new understanding is helpful for you in maintaining optimal performance and health!

If you want to explore this with a professional reach out! You can contact me by emailing info@smartmovementpt.com or set up an appointment HERE. If you do not live near me in the Bay Area I do tele-visits utilizing video chat to discuss all of this and provide analysis and coached exercises in addition to in-person visit options.

-Dr. Jaimie Harrow,

Physical Therapist


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© 2018 by Jaimie Harrow.