What exactly is 'core stability'? Well it means many different things to different people, but within the world of physiotherapy the term has come to symbolise a series of exercises that asks you to brace and pull in your deep abdominal muscles as you perform different movements. These are commonly prescribed by many physios to those with longstanding back pain, but, do they help, do they make a difference, and what's the evidence for using them?
To try and answer these questions I'm delighted to welcome Ben Smith to 'The Sports Physio'. Ben is an MSK Physiotherapist working in the NHS in Derby. He’s currently completing a Masters at Nottingham University and is working towards a PhD application in relation to PFJS. His specialist interest is integrating evidence into practice, particularly with spines and knees, and can be followed on Twitter @benedsmith Ben has very kindly written an extremely well researched and evidenced based piece looking at the use of core stability exercises for chronic low back pain.
Now before we get started, this is a subject I've touched on before in my rants and ravings online and those who know me will already know my own strong, cynical and sceptical views on this subject, that being I have very little time or patience with core stability exercises within physiotherapy and that I find the practice of asking those with back pain to brace and clench things tight and rigid, absurd and complete nonsense, so to avoid the screams, accusations and shouts of bias and unfairness I will extend an invitation to anyone willing or wanting to defend the role of core stability exercises the chance to write a reply article in response to Ben's, just leave a comment below with your request and I will be in touch!
So without further ado lets get into it and I'll hand over to Ben as we delve into the role of 'Core stability and chronic low back pain'
Physiotherapy treatments for LBP range from spinal manipulations, mobilisation, advice, general exercises and specifically tailored exercises (Liddle et al., 2009). Despite doubts raised about its effectiveness compared with other forms of treatment (May et al., 2008), the most frequently given exercise by physiotherapists is core stability (Liddle et al., 2009). The exercise has become the unquestioned treatment of choice for physiotherapist.
This blog will examine relevant evidence surrounding the effectiveness and the underpinning physiological effects of core stability exercises for chronic LBP.
It has been suggested that in normal people the muscle transversus abdominis (TrA) activates prior to limb movement in an anticipatory feed forward mechanism, and further suggested that this activation is delayed in patients with chronic LBP (Hodges et al., 1996, 1999; Richardson et al., 1999). It was therefore hypothesised that addressing this delayed feed forward mechanism through therapeutic exercise would have a positive effect on patients with chronic lower back pain, furthermore that people without current symptoms, but a history of symptoms, would be at a reduced risk of re-injury by following this treatment protocol (Hodges et al., 1999). An exercise regime aimed at isolating TrA was then developed, designed to retrain motor skills and ‘reset’ the delayed feed forward mechanisms (Richardson et al., 1999).
Underpinning physiological effects
The hypothesis that TrA training can have a positive impact on patients with chronic LBP is based upon two premises. Firstly, that TrA is the key component to spinal stability, and secondly that training can ‘reset’ the delayed timing issue.
The first premise, that TrA is the key component to spinal stability, is a huge assumption, and a theory that fails when tested. It centres upon the biomedical model of causation, as described by Bradford Hill (1965). It is a model of causation whereby biological changes are used to describe states of illness. It makes assumptions based upon the considered ‘normal’ state in which a body should be (Tyreman, 2006), with any variations from this ‘normal’ state being considered abnormal, and ultimately leading to illness. What we know is that this model is extremely simplistic, and fails to take into account psychological and social factors (Tyreman, 2006).
More recent studies have shown that the onset timing of TrA does not have an ideal pattern in pain free subjects, and that variance is ‘normal’ (Mannion et al., 2008; O Vasseljen et al., 2009). Furthermore, any delayed timing in chronic LBP patients has not yet been consistently found in subsequent research. Gubler et al. (2010) carried out a cross section study using ultrasound to time the onset of TrA during shoulder flexion in 48 patients with chronic LBP and 48 pain free patients. It was high quality, with little to no bias and suitable control and group allocation. They concluded that no difference exists between chronic LBP patients and pain free subject for TrA activation timing during shoulder flexion.
The second premise, that TrA training can improve delayed timing, also fails when testing. Ottar Vasseljen et al. (2012) carried out an eight week RCT (N=109) looking at one on-one core stability training versus one-on one sling exercises and group general exercises. Outcome measures were pain and disability, but also onset timing of TrA during shoulder flexion. They found that after 8 weeks of training there was no difference between groups on pain, disability and most importantly TrA onset timing with shoulder flexion. Generally it was a methodologically robust study with suitable power calculation, intention to treat analysis, low attrition and appropriate allocation. Unfortunately bias could have entered the study (in either direction, depending on the assessor’s preference), since the assessor was not blinded to group allocation during TrA timing analysis.
It can be concluded that; there is no consistent evidence chronic LBP patients have a delayed onset of TrA activation, any delay is not important to the causation of their LBP, and TrA training does not improve any timing issues.
There have been many published research articles looking into the effect of core stability exercises in patients with chronic LBP, some higher quality than others. However, no randomised control trial has shown that core stability is more effective over general exercises for pain, function or disability in patients with chronic LBP. A 2008 systematic review which, included trials up to 2006, concluded that core stability exercises are unlikely to produce betters outcomes over other form of exercise (May et al., 2008).
Petrofsky et al. (2008) and Pensri & Janwantanakul (2012) state that core stability exercises reduced pain in chronic LBP patients, but with no comparison with general exercise, outcomes only taken on discharge and no subject allocation information, the results are inadequate to enable generalisations.
Ferreira et al. (2007) state that the short term effect of core stability is greater than general exercise for chronic LBP. They undertook a pragmatic RCT with 240 participants with chronic LBP of three or more months’ duration. They compared three different treatment protocols lasting eight weeks; general exercise, manipulation and core stability exercise. The general exercise group was a class based group involving general exercises based on the ‘Back to Fitness’ program by Klaber Moffet and Frost (Klaber Moffett et al., 2000). The core stability group received 12 individual treatment sessions over eight weeks based on Richardson et al. (1999), with the use of an ultrasound machine to aid in muscle recruitment and biofeedback.
At 8 weeks the core stability group had significantly better function, as measured by Patient-Specific Functional Scale (Westaway et al., 1998). However, pain and disability at eight weeks were the same in all groups. Furthermore, all outcomes at 6 and 12 months were similar in all groups. Pain was measured on a visual analogue scale, where 0 represents no pain and 10 worst pain imaginable, and disability by the Roland Morris Disability Questionnaire (RMDQ). This is an extremely reliable and valid outcome measure for pain, function and disability in chronic LBP (Beurskens et al., 1995; Roland et al., 1983).
The internal validity of Ferreira et al. (2007) is low. Intention to treat and sensitivity analysis were avoided. Coupled with a high, un-even, drop out rate, (9% for general exercise compared with 19% for core stability) this omittance lowers the robustness of the results and usefulness to the practitioner as it biases the results in favour of core stability. If core stability patients not having benefit from treatment drop out more frequently than the general exercise group their exclusion from the analysis would lead to an exaggeration of the effect of core stability.
Ferreira et al.'s (2007) short term results are contradicted by Koumantakis et al. (2005) study. Short term outcome measures at eight weeks showed core stability had significantly worse fear avoidance scores compared with general exercise on the Roland Morris Disability Questionnaire (RMDQ).
Koumantakis et al. (2005) had a slightly different methodology to Ferreira et al., (2007), comparing general exercises with general exercises plus core stability over eight weeks, and the general exercises were not based on the ‘Back to Fitness’ program by Klaber Moffet and Frost, (2000), but were non specific mat exercises.
Koumantakis et al. (2005) adjusted the total class time according to time of muscle activation, and as a result total class time for the core stability group was almost double that of the general exercise group (99 minutes v 180 minutes), biasing results in favour of the core stability group.
Koumantakis et al. (2005) had a larger attrition rate than Ferreira et al. (2007), however they carried out a sensitivity analysis, with intention to treat producing similar results to per protocol analysis, improving internal validity of results since this adjusts for the uneven drop out rates in their analysis.
Comparison and generalisation between these two studies may not be possible; the majority of patients for Ferreira et al. (2007) were unemployed, from low socio-economic groups whereas all patients for Koumantakis et al. (2005) were employed. It has been shown that people from low socio-economic groups are at a far greater risk of developing chronic LBP, and may have worse results with therapy (Katz, 2006). In addition, all patients for Koumantakis et al. (2005) must have had a x-ray or MRI to be included. It has been shown that patients who have x-rays or MRIs may have better short term satisfaction, but long term fear avoidance is generally worsened (Chou et al., 2007). Therefore, comparison of improvements in RMDQ scores between studies is of limited value.
Despite being unable to compare results directly, the higher internal and external validity ofKoumantakis et al. (2005) means we can trust the result more, and make generalisations better, which is further discussed in the conclusion.
Cairns et al. (2006) was another pragmatic, multi-centred, RCT comparing core stability exercises with conventional physiotherapy for chronic LBP. Both groups received 12 weeks of physiotherapy on a one to one basis, for up to 12 sessions. Both groups were allowed, if the physiotherapist felt warranted, manual therapy and electrotherapy. It was a comparatively high quality RCT, with power calculation, sensitivity analysis and a robust methodology. Attrition rates were high at 30%, but were comparable with Koumantakis et al. (2005), potentially indicative of patients with chronic LBP.
External validity of Cairns et al. (2006) as a stand alone RCT is low, since ‘distressed patients’ were excluded from the study, and it is known that many patients that present with chronic LBP are classified as distressed (MC Cairns et al., 2003). However, Cairns et al. (2006) included the RMDQ as an outcome measure, and in agreement with Koumantakis et al. (2005) and Ferreira et al. (2007) found no significant between group difference at 6 months and 12 months. Furthermore, they found short term outcomes were the same for both groups.
Although not statistically significant, the general exercise group had an improvement in 57% of patients, compared with 48% in the core stability group, and had a lower average number of treatment sessions. Cost was not calculated nor compared, but this finding is corroborated by Critchley et al. (2007) who did calculate cost in a comparison of traditional physiotherapy, with core stability and group pain management. Critchley et al. (2007) looked at the Roland Disability Questionnaire in 212 patients up to 18 months after discharged and found no difference between pain and disability in the three groups. However, cost was significantly lower for group rehab and traditional physiotherapy when compared with core stability.
These four trials are further strengthened by Lewis et al. (2005), Gladwell et al. (2006), Norris & Matthews (2008), Rasmussen-barr et al. (2009) and Muthukrishnan et al. (2010) who found that core stability training compared with control groups had no improvement in outcomes measures. Control groups being; group rehab, no treatment, information leaflet, daily walks and general physiotherapy respectively.
It can be concluded; there is some agreement that core stability offers no additional benefit in long term outcomes of pain, function and disability over general exercises, plus or minus other forms of physiotherapy treatment. It is likely to be more costly, and there is some evidence to suggest that fear avoidance in the short term may be worse.
This blog has questioned the relevant evidence surrounding the effectiveness and the underpinning physiological effects of core stability exercises for chronic LBP.
Despite being the most common form of physiotherapy treatment for patients there is a lack of evidence to support its use.
Any benefit over no treatment/minimal treatment can be attributed to the general exercise effect.
Core stability should not be used in patients with chronic LBP and a more general, functional,exercise regime used instead, as proposed by Klaber Moffet and Frost (Klaber Moffett et al., 2000).
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