The myth of core stability


Editor’s Selection IconThis post was chosen as an Editor's Selection for ResearchBlogging.orgFads come and fads go, and no more so than in managing back pain. One of the more durable fads has been the plethora of exercises to ‘strengthen the core’. I’ve been searching for a good review of the literature on core stability, and surprisingly found one in a journal I rarely read: Journal of Bodywork & Movement Therapies.

Eyal Lederman has written an extensive critical review of the use of core stability in back pain rehabilitation, and although there is a lot of material covered in the review, it is summarised nicely and the reference list alone is worth getting the article!

The basic premise of core stability was a finding that in people with chronic low back pain, there are changes in motor control of the trunk muscles. Along with some of the other underlying beliefs about back pain such as the need to avoid ‘using the back like a crane’ and probably the Pilates movement, the school of core stability was born. Lederman summarises these assumptions as:

  1. That certain muscles are more important for stabilising the spine than other muscles, in particular the transverse abdominis
  2. That weak abdominal muscles lead to back pain
  3. That strengthening abdominal or trunk muscles can reduce back pain
  4. That there is a group of ‘core muscles’ that work independently of other trunk muscles
  5. That back pain can be improved by normalising the timing of core muscle activation
  6. That there is a relationship betwen stability and back pain

Now apart from the very real concern that I have of patients being told they have ‘an unstable back’ – and then believing that they must never ever move without tummy tucking and bracing or their back will ‘go out’ – several of the assumptions simply don’t hold water at face value.  When the body is seen as a whole, why would a specific group of muscles be more important than another in protecting against back pain? Are backs meant to be ‘stable’ and unmoving? Just take one look at a group of people working together to move house – all manner of movement patterns emerge, and not one of them strictly follows the ‘stabilise your core then move’ edicts.  For that matter, the ‘semi-squat’ or the ‘neutral lumbar curve’ are similarly not there!

Lederman begins the review of core stability by examing the role of the transverse abdominis. I wasn’t aware, but a certain proportion of people don’t have a ‘normal’ TrA, or it is fused to the internal oblique muscle, and this is a normal variation.  Do these individuals have more or less back pain than others? And how do they stabilise their trunk?  He also points out that pregnant women’s TrA lengthens and as a result, while all nonpregnant women can do a sit-up, 16% of pregnant women cannot.  There was no correlation between sit-up performance and back-ache – the strength of the abdominal muscle was not related to backache (Fast et al, 1990).  Desite this, pregnant women are often given core stability exercises to ‘retrain’ the abdominal muscles and as a treatment for back pain – and there is (to quote) ‘little evidence that localised musculoskeletal mechanical issues, including spinal stability play a role in the development of low back pain during pregnancy.’  Lederman goes on to explore a study where a CBT vs standard physiotherapy RCT was conducted – out of 869 pregnant women, 635 of them were excluded because they recovered spontaneously within a week of delivery.  Hardly long enough for TrA to ‘recover’.

Lederman next examines the timing of activation of TrA during rapid exercise of the arms and legs. Hodges and Richardson (2003) found that TrA activation was delayed in people with low back pain, and it was assumed that it had a role in controlling spinal stability.  While it’s understandable to seek simple answers, and this seemed logical at face value, Lederman reminds us that all structures in the body are connected in many dimensions.  It’s hard to see this when working from a muscle atlas, but in reality, although the TrA is a ‘main’ muscle involved in spinal stability, in fact it is one of many – and changes in timing of its activation may be a protective mechanism for people with low back pain rather than a causal mechanism – a bit like that automatic withdrawal response we get when touching a hot surface.  Maybe movement pattern changes occur in response to the threat of pain rather than cause pain.

I won’t go into much more of this paper, but I hope you can see that there are some basic assumptions about the role of core stability that need to be re-examined before deciding that they hold in all cases.  Lederman looks at strength, coordination, motor learning, and the process of acquiring movement patterns that are specific to the movements needed.  I’ll look at the use of core stability in treatment tomorrow.

The question to pose is, I think, how one overly simplistic approach to back pain can take hold and grow to the extent the core stability industry has grown.  Is it the simplicity of it in the first place? After all, it appeals because it is simple and biomechanical and relatively understandable.  The exercises themselves are easy to do (not quite so easy to do well!), and for the couch potato amongst us, they don’t require lots of running about and huffing and puffing.

Maybe they help initially to reduce the fear that people have that moving and becoming aware of their back will overwhelm them with pain and they will be helpless.  It has allowed the group of professionals with the greatest face value in terms of trustworthiness about moving to introduce exercise at a very low-key and nonthreatening way.

But at the same time, maybe it has also introduced to yet another group of patients, a set of ‘safety behaviours’ that must be employed before doing any sort of movement involving the spine – reinforcing their fears about harm to their spine if they don’t do things very, very carefully.

Lederman, E. (2009). The myth of core stability Journal of Bodywork and Movement Therapies DOI: 10.1016/j.jbmt.2009.08.001

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