History and presumption are often responsible for concepts and terms being accepted without question. On reviewing the basis on which many of these terms exist reveals the existence of myths rather than fact. The problem here lies that when these terms become accepted into our language an assumption of universal understanding is made. Core stability would appear to be a term that has grown out of a combination of urban myth and scientific research. Much emphasis in Western Medicine is placed on evidence based pracitice. While gold standards are created for treatments and interventions some of the concepts on which they were originally derived may not have been based on scientific evidence (Higgs and Jones, 1995).
In the continually growing and developing world of health and fitness, sports medicine, exercise physiology, physiotherapy and spinal rehabilitation core stability has become a very popular term. A review of the literature on core stability provides an irregular and inconsistent array of definitions and concepts. This lack of stability in definition is not just restricted to the academic world. The practical use of the term by coaches, trainers and medical personnel provides confusion at both an inter and intra-professional level and this is reflected in the understanding of athletes, patients and clients to the term. An example of the above problem is on review of medical referrals to physiotherapy clinics that request that a patient’s core stability is examined with reference to their back pain. In this example the doctor may consider that poor core stability is a cause of the back pain or a secondary problem that needs to be managed. Are the two professionals operating on the same wave length with reference to what core stability is? Some definitions suggest that the abdominal musculature and the ability of an individual to control these muscles is the essence of core stability (Lawrence, 2003). This definition would appear inadequate for many academics and health professionals. Core stability may be referred to as trunk control by some professionals. This definition encompasses greater anatomical involvement, possibly extending from the muscles controlling the neck extending inferiorly to the structures providing pelvic stability and making up the pelvic floor. Clearly this incongruity of definitions would result in the athlete, patient or client receiving very different regimens of training, treatment or rehabilitation.
The terms strength and stability are not synonomous (Gibbons and Comerford, 2001a). Gibbons and Comerford (2001a) described strength as being based on the assessment of muscle function with load while stability was determined by assessing motor control regulation of muscle stiffness with no external load. Core stability and core strengthening are terms that appear to be used interchangably however the above definitions highlight how this may be inappropriate . The neurophysiological goals behind strengthening and stability programmes are individually very different. An example of this can be seen from the intensity that muscle contractions are performed, for a strengthening programme contractions at 60-80% of a maximal voluntary contraction are routinely used as the training intensity and this can result in muscle fibre hypertrophy (Astrand and Rodahl, 1986). For stability programmes the emphasis has been on improving neuromuscular pathways of muscles that work tonically at low levels thus requiring excellent endurance capacity. This has been shown to occur during exercise programmes that work at intensity levels between 3 and 40% of a maximal voluntary contraction (Davidson and Hubley-Kozey, 2005; Hagins et al., 1999).
Conversely there is also a lack of consensus regarding the precise biomechanical definition of instability. In the literature review by Hagins et al. (1999) they concluded that there was no current method, including x-ray examinations, that could reliably demonstrate the presence of instability. Furthermore, despite the lack of agreement on a definition, lumbar instability is a commonly used diagnostic category that frequently is intended to guide physiotherapy treatment (Hagins et al., 1999).
The concept behind core stabilisation exercise programmes has been to increase muscular control of the lumbar spine. The role of the neuromuscular system in maintaining a neutral position of the spine to prevent excessive translations and to control force distribution through the spine makes up the cornerstone of core stability exercise systems (Panjabi, 1992a and 1992b, Comerford and Mottram, 2000; Norris, 2001; Westlake, 2002 and 2003). On review of the myriad of methods employed to achieve such claimed states of stability one can find significant variations in application of techniques and proposed benefits (Blount, 2000; Bonelli, 2000; Boyle, 2004; Cook, 2003; Craig, 2003, Frediani, 2003; Lawrence, 2003; Liebenson, 2003, 2004a, 2004b, 2004c, 2004d; Stott, 2002; Westlake, 2002). Evidence behind the efficacy of these techniques needs to be investigated as it would appear that the base of foundation studies is relatively small yet the extrapolation of these results to many exercise systems has been vast. The validity of such assumptions needs to be investigated as core stability training programmes have rapidly become the essential ingredient of many rehabilitation and performance programmes (Cook, 2003; Lycholat, 2004).
This study analysed the published material relating to the concept of core stability and reviewed the quality of the available evidence using an established guideline. The guideline chosen for this study was developed by the Scottish Intercollegiate Guideline Network (SIGN) and was most recently reviewed and updated in May 2004 (SIGN, 2004). Clinical guidelines are becoming increasingly popular as health professionals become more aware of the need to practice in accordance with the best available research evidence (Baker and Burns, 2001). The SIGN 50 (2004) system grades guidelines according to the strength of supporting evidence (SIGN, 2004). The grading system is ultimately a combination of objective assessment of the design of each study and a more subjective judgement on the consistency, clinical relevance and external validity of the whole body of evidence (Guyatt et al., 1995). The aim of this study was to determine whether this popular term has a valid basis from a biomechanical, anatomical and physiological perspective. This research reviewed definitions, models and methodologies for measuring and analysing core stability and its related terms. The impact that core stability can have on other pathologies was also examined. Further aims of this work were to produce the first known clinical guidelines for core stability based on evidence.
The objective of this review was to evaluate the concept of core stability by critically examining the evidence from the literature in relation to key research questions using an established method for guideline development. The ultimate objective was to determine if the term core stability had a sound scientific basis.