Does the inner and outer core theory actually hold true?

There still seems to be a lot of controversy around the significance of the “inner core”. This topic just wont seem to die.

For those who aren’t familiar with this concept it’s basically the notion that if an individual has a “dysfunctional” inner unit this will in turn increase their potential for back pain & core dysfunction.
Remember the saying “ You cannot fire a cannon from a canoe “

Well one of the original papers that this concept was founded on was the Hodges & Richards paper (1). Their work suggested that the inner core muscles (Transerse Abdominals TrV) should fire just before the larger “outer unit” muscles as to increase stabilization of the spine

They advocated that dysfunction of the inner unit was the main reason for pain pathologies and a lack of core stability.

The counter argument is that more recent research has shown that the transverse abdominals does not always activate prior to the movement of the extremities (Allison GT et al 2008).
Stuart McGill PhD discredited the claims that TrA is a primary ‘core stabilizer,’ noting that biomechanically; no single muscle can dominate core stability (6).
McGill’s has also presented evidence that abdominal hollowing manoeuvre contributed little to spinal stability, finding instead that bracing of the entire abdominal region improves lumbar stability far better than hollowing alone. (5)

Additionally the research paper: “The Myth of Core Stability” beautifully presents evidence that there is very

little to support a correlation between core strength & back pain in the following groups:

• Pregnant females
• Obese or overweight individuals
• Muscular injured individuals – i.e. surgically operated on

So all in all the inner theory is dead right?

Well No but what then is the role of TrA?

TrA like all muscles that cross the “core” contribute to core stability, especially considering that it has deep insertions into the thoracolumbar fascia.

However many muscles cross the “core”

To name just a few:

1. Iliacus
2. Psoas Major/Minor
3. Lat’s
4. Gluts
5. TrA
6. Internal Oblique’s
7. External Oblique’s
8. Rectus abdominis

Each of these muscles has a stabilizing effect at the level of the “core”.
TrA is likely no more or less important than other muscles at the “trunk” however if the aetiology of the dysfunction is a weakened muscle group and strengthing exercises of this group reduce pain or dysfunction, then it stands to reason that this is a valid assessment to assist in core “dysfunction” .
More so this has being shown to work in both a clinical and research settings

Heres an example: 

Multifidus ( another “core” back muscle ) reduced size was found in lower back pain patients . These where even elite level athletes. Specific retraining of this muscle group resulted in growth of the muscles and concomitantly decreased the levels of back pain (8)
There’s always controversy in science and interestingly enough a later paper by Richardson (2002) showed that contraction of the TrA significantly reduced slackness in the sacroiliac joint vs a bracing action that utilized all the lateral abdominal muscles (7).

Hmmmm kinda interesting, don’t you think?

So there it is:

TrA is most certainly not the ‘holy grail’ of core stabilizers, but it is however still a muscle with significant stabilizing capabilities at the “core”.

Basically this is how I’ve had it clinically work in the past:

(And no I’m not a qualified physiotherapist)

But I do work by one simple rule and that is this:
If what I do makes your movement better or takes the pain away permanently, then I’m most likely on the right track

Just as having weak gluts doesn’t automatically predispose you to knee pain, so to having a weakened TrA doesn’t necessarily mean you’ll have back pain but if strengthening the gluts, TrA or any other muscle for that matter, takes the pain away, keeps it away & helps improve your overall control, then I can only see it as the solution to the problem.

At the end of the day muscles control movement, if the movement and joint actions are well controlled (even with a few “sleepy” muscles) you probably wont run into many problems but if the movement is poorly controlled and pain is present due to weak muscles, then strengthening those muscles and teaching the correct control strategies will likely be your biggest key to success.

REFERNCES:

1. Richardson entitled Therapeutic Exercise For Lumbopelvic Stabilization: A Motor Control Approach For The Treatment And Prevention Of Low Back
2. https://bretcontreras.com/innerouter-core-is-b-s-another-interview-with-jurdan/
3. CPDO Online Journal (2007), June, p1-17. The Myth of Core Stability Professor Eyal Lederman
4. Lund et al. 1991. The pain adaptation model: a discussion of the relationship between chronic musculoskeletal pain and motor activity.  Can J Physiol. Pharmac. 69:  683-694.
5. Grenier & McGill 2007, APMR 88:54-62),
6. Kavcic et al. 2004, Spine 29(11):1254-65)
7. Richardson, Carolyn A. The Relation Between the Transversus Abdominis Muscles, Sacroiliac Joint Mechanics, and Low Back Pain
8. Effect Of Stabilization Training On Multifidus Muscle Cross-Sectional Area Among Young Elite Cricketers With Low Back Pain Julie Hides, PhD1,  Warren Stanton, PhD2,  Shaun McMahon, PhD3,  Kevin Sims, PhD4,  Carolyn Richardson, PhD5