Having examined the effect of core training on performance and injury prevention, the next question is who is it most likely to benefit? Very few treatments or exercises can be recommended to everyone and yet core stability has at times been sold as a must for all runners. Like any strength and conditioning option there are some that will gain a great deal from core work and others that would be better focussing their training elsewhere. So how do you decide if core work is for you?…
The 'core' isn't well defined which is part of what makes it difficult to fully assess. I consider it to be an area stretching from the hip and pelvis to the base of the sternum. You might find this controversial but I consider it to be an area that is inherently stable.
The base of the core is the pelvis – a strong bony ring that is made more stable by weight-bearing and is supported by a system of strong ligaments. The spine is at the centre of the core and has 4 different stabilising systems – bony, ligamentous, muscular and fascial. Bony stability comes from the way each of the vertebrae lock together like 3 dimensional jigsaw pieces preventing excessive movement. Each vertebrae is attached to its neighbour by 5 or 6 strong ligaments providing further stability. Then a system of 29 pairs of muscles support the spine and pelvis during movement while everything is enclosed within the the thoracolumbar fascia which wraps around the trunk like a corset. Above the lumbar spine is the diaphragm and beneath it the are pelvic floor mucles – these are thought to form the roof and base of a supportive cylinder with the spinal muscles and fascia forming the sides. Add to this the protective nature of the rib cage that encloses the thorax and you have to ask does this really need additional stability?
Where core stability work is most likely to help is if any of these stability systems are compromised, this might happen with reduced bony stability, decreased ligamentous support or poor muscular control. A number of conditions might effect this;
Hormones released during pregnancy and while breast feeding increase ligament laxity to allow birth to happen. This combined with the effect labour and pregnancy has on abdominal and pelvic floor muscles could affect spinal stability. These changes are expected to resolve once breast feeding is stopped but some women have ongoing issues with low back pain and may struggle with recruiting abdominal and pelvic floor muscles.
For more information on exercise during or after pregnancy see the American College of Obstetricians and Gynaecologists (2003) guidelines. They state that,
“Many of the physiological and morphological changes of pregnancy persist for four to six weeks post partum. Thus, exercise routines may be resumed only gradually after pregnancy and should be individualised.”
A spondylolisthesis is a forward slippage of one vertebrae on another. It is often caused by trauma and tends to cause pain with extension based movements. Despite this many people with a mild spondylolisthesis may have no symptoms, perhaps because ligamentous and muscular stabilising systems continue to support the spine.
Hypermobility syndrome is relatively common, more so in women than men. It involves an increase in soft tissue flexibility including increased ligament laxity. This can effect ligamentous stability and movement control as there is thought to be a reduction in proprioception which is important for balance and control of movement. For more information see @AdamMeakins' work on hypermobility in sport or Hypermobility Hope an interesting and helpful blog from Chelsea, who has hypermobility syndrome.
This is more difficult to define and describe and hard for someone to assess themselves. It might be that you find any core stability or balance exercises very challenging and this would be an indication that they may be of benefit to you.
For runners I would recommend 2 fairly simple tests used by Kibler (2006) – single leg balance and single knee dip. Both are fairly functional to runners and test both balance and core stability. More details on how to do this in assessment and rehab of balance.
The pictures below are reproduced from Kibler (2006) freely available online here. Note the first picture shows single leg balance with a level pelvis, while second picture demonstrates hip adduction during single knee dip test.
In addition you could use a test used by McGill et al. (1999) – the side bridge. They found that on average men could maintain a side bridge for 94 secs on the right and 97 on the left. Women held for 72 secs on the right and 77 on the left. All subjects were young and healthy. Leetun et al. (2004) also studied side bridge and reported an average of 58.9 secs for women and 83.4 for men. Ability with side bridge might suggest glutes endurance and Leetun et al. found it to be significantly correlated with hip abduction and external rotation strength. It also links with recent work by Reiman et al. (2012) who found high Gluteus Medius activation with side bridging. In short it is a measure of stability that also links with glutes strength and for which we have at least some idea of 'normal'.
Side bridge test from Leetun et al. (2004) freely available online here (80's track suit optional!)
How the lumbar spine moves can be an indication of whether you may benefit from core work. This is very difficult to assess yourself and I would recommend a professional opinion, especially if you have back pain. Work by O'Sullivan (2005) has helped classify movement 'dysfunction' into categories. Describing movement dysfunction in detail is complex and beyond the scope of this article but I highly recommend his work for more information.
So, for an idea of your own core stability try the following 4 tests;
- Single leg balance – maintain sturdy balance for at least 10 seconds keeping the pelvis level
- Single knee dip – aiming for at least 10 reps without adducting the hip or excessive trunk or pelvic movement
- Side bridge – aim for roughly 1 minute for women and 90 seconds for men
- Flexion test – in standing try and touch your toes then return to an upright position. Aim for a smooth pain free movement without needing support from your arms.
Koumantakis et al. (2005) compared stability work with general exercises for low back pain and concluded,
“Stabilization exercises do not appear to provide additional benefit to patients with subacute or chronic low back pain who have no clinical signs suggesting the presence of spinal instability.”
Although this study is on patients with back pain it does provide some support for the argument that core stability training is unlikely to be beneficial to those with no issues with stability.
Hicks et al. (2005) tried to determine if there were clinical signs that might indicate if stability work was more likely to be effective in managing low back pain. They found 4 signs that were suggestive of a positive outcome;
- Age less than 40
- Evidence of 'aberrant movement pattern' in lumbar spine (painful arc of motion, using hands on thighs for support during lumbar spine movement etc.)
- Straight Leg Raise greater than 90° (suggestive of increased general flexibility)
- Positive Prone Instability Test
Of these age was the most strongly predictive of positive outcome with stability exercises.
From the research I've read specific to athletes only Akuthota et al. (2007) described who should have core stability exercises prescribed and they used the guidance above from Hicks et al. (2005). Other papers, such as Fredericson and Moore (2005) suggest core training is essential for runners but with little evidence to support these claims. Their 20 page article contains just 14 references and only 1 of these papers involved runners.
Consider your goals
What are you hoping to achieve with core training? If it's improved performance there may be more effective alternatives as discussed previously. It may have a role in injury prevention if you have core stability issues although the research isn't clear on this. Simply being sensible with increasing running distance and intensity may be more effective. Where core training is perhaps most likely to be useful is in injury management, specifically back pain, if you have signs of reduced core stability (as discussed above).
Macedo et al. (2009) performed a systematic review of 'motor control' (another term for core stability) exercises for persistent non-specific low back pain. They found that motor control work was 'superior to minimal intervention' and was beneficial when added to other forms of treatment. It was not found to be superior to any other forms of exercise. Similar findings were reported elsewhere in the research.
This means core work can be a safe and effective option for managing low back pain although there is little evidence to suggest it is better to other types of exercise.
I acknowledge there are a considerable amount of limitations to these conclusions the largest being that most of the research used here was actually done on back pain patients rather than runners. In reality there appears to be little or no research specific to runners that tries to identify which specific athletes will benefit from core work. As a result I've had to use what research there is from other areas along with clinical reasoning to provide some level of recommendation. Research on core training is a minefield! Each study I have read has pointed me in the direction of 4 or 5 more! For every definite conclusion one study makes, another seems to make the opposite. Of all the topics I've written about for RunningPhysio this has been the most complex and multifactorial. So if you have different views or recommendations I would love to hear them! Feel free to add them in the comments section.
Nothing in physiotherapy is set in stone and I would view my recommendations as a form of guidance rather than rigid rules – there simply isn't the evidence for them to be anything more than suggestions!
In summary you may be more likely to benefit from core stability training if you are post pregnancy, have a diagnosis of hypermobility syndrome or spondylolisthesis or have difficulty with balance or trunk movement control. Younger runners may be more likely to benefit than older runners. In addition you may want to continue core training simply because you enjoy it, or because you've found it helpful for your needs. If this is the case there is certainly no need to abandon it!
Further research is needed to determine who is most likely to benefit from core training and in what way. There is evidence that supports the theory but not necessarily evidence that proves the results of core training. Runners as a population have not been extensively studied in this field and we need a number of high quality trials before firm conclusions can be made.
A final consideration here that is worth mentioning is that 'reduced stability' does not necessarily mean your spine is unstable. A genuinely unstable spine usually only occurs as a result of serious trauma that severely compromises bony or ligamentous stability. This type of situation is a medical emergency and won't be fixed by a few sessions on a gym ball! When we describe 'reduced stability' we tend to mean that the spine has lost some of its ability to control movement but as a whole is still 'stable'. For health professionals advising core work I recommend careful communication with your clients to ensure they don't leave with the impression that their spine is unstable, fragile or easily damaged.
A brief closing point on back pain – if you do have issues with back pain please read our acute back pain guide and as ever if in doubt get it checked out!
Coming soon in our core stability series we'll examine core exercises and how you do them – should you use abdominal bracing or hollowing (or neither) during core work? Are you aiming to keep the spine still in 'neutral' or move it through range? Do you benefit from using unstable surfaces such as wobble boards, BOSUs and gym balls?
All will be revealed….just as soon as I've waded through the vast amount of research…..!