Many researchers and authors agree that the key aim of core stability programmes is to optimise the performance of muscle activity around the lumbar spine to prevent harmful movement (Lawrence, 2003; Norris, 2001; Richardson et al., 1999; Westlake, 2003). Thomson (2002) concluded following an evidence based review of the literature on chronic low back pain that individuals with greater ranges of spinal motion have increased risk of future troubles and that endurance and not strength related to reduced symptoms. The developing core stability concept recommends that the spine must be in a stable neutral position before developing forces to enhance performance (Stott, 2002; McGill et al., 2003; Panjabi, 1992a). The neutral position of the lumbar spine is described as a position of lordosis where the pelvis is positioned somewhere inbetween a full anterior and posterior pelvic tilt (Stott, 2002). In this position there is minimal stress through the facet joints, intervertebral discs, ligaments and joint capsules (Panjabi, 1992a). The deep stabilising muscles which are believed to be tonically active, are minimally active in the neutral position therefore minimising the potential for muscular fatigue (Cholewicki et al., 1997; Hodges et al., 2000). It has been hypothesised that fatigue of the stabilising muscles is a major contributing factor to lumbo-pelvic dysfunction (Thomson, 2002). Lack of muscular control at a motion segment could adversely effect spinal mechanics as the muscular system has a major role in spinal stability as discussed in Chapter V.
Cholewicki et al. (1997) demonstrated that modest levels of coactivation of the paraspinal and abdominal wall muscles were necessary to maintain a stable spine in a neutral position. Continuous, low grade muscle activation of these muscles should maintain stability with all activities of daily living. Studies by Luoto et al (1995) suggested that it is not absolute strength of the local stabilising muscles that prevents injury or lumbo-pelvic dysfunction but endurance capacity or muscle control.
A number of researchers have observed alterations of the motor control system following injury (Burnett et al., 2004; O’Sullivan et al, 1997; Richardson et al, 1997). It would appear that these motor disturbances such as multifidus inhibition following back pain, compromise spinal segmental stability (Hides et al., 1996). McGill et al. (2003) summarised spinal stability as coming from active and passive stiffness. Passive stability can be lost through tissue damage and active stiffness may be compromised by disturbed motor patterns following injury (McGill et al., 2003).
It has been suggested that pain and dysfunction are related (Richardson et al., 1999). A number of studies have demonstrated that a decrease in the cross sectional area of local stabilising muscles on the ipsilateral side to the symptoms existed in back pain subjects (Hides et al, 1994 and 1996). There has been evidence of specific loss of cross sectional area of the lumbar multifidus (Hides et al, 1994) and psoas major (Gibbons et al., 2002) that corresponded with specific vertebral levels. Hides et al (1996) found that on resolution of pain there was still dysfunction present with the multifidus muscle in terms of decreased cross sectional area and muscle activation patterns. To optimise this situation it would be necessary to improve the muscle activation patterns of multifidus as well as rebalance the muscle mass in terms of cross sectional area. The literature on low threshold training for the local stabilising muscles places an emphasis on the need for muscle contractions to be performed at low percentages of a maximal voluntary contraction (Richardson and Jull, 1995; Richardson et el., 1999 and 2002). These levels are below those of strength training that result in hypertrophy. While it has been hypothesised that neuromuscular pathways appear to be enhanced with low threshold training (Cholewicki et al., 1997; Hubley Kozey and Vezina, 2002a), herein the question lies, what mechamisms can be employed to return deep stabilising muscles such as multifidus to normal physiological proportions? A similar phenomena of muscle wasting and decreased activation through reflexive inhibition has been observed at the patellofemoral joint (Arvidsson et al., 1986). Dysfunction at the patellofemoral joint results in inhibition of the vastus medialis obliques (VMO) muscle (McConnell, 2002). Patellofemoral joint rehabilitation programmes generally encourage isolated VMO activity first in controlled ranges then progress to more dynamic and functional tasks (McConnell, 2002). The work of McConnel (2002) has further parallels with lumbopelvic stabilisation programmes in that they both acknowledge the principal of placing the osseous structures in neutral positions. The McConnel (2002) programme can involve taping techniques to keep the patella from maltracking whilst performing isolated VMO contractions (McConnell, 2002) compared with lumbopelvic programmes that concentrate initially on achieving a neutral pelvic position (Stott, 2002). The apparent reflexive inhibition of these muscles has been shown to be reversed through specific active exercises (Cowan et al., 2002; Crossley et al., 2002; Hides et al, 1996; McConnel, 2002). Hides et al., (1996) found that multifidus CSA returned to normal levels following stabilisation exercises. It could be postulated that the return of multifidus CSA is related to the normalisation of tonic neural activity. This is an area of research that warrants further investigation.
Overload training is a method used to increase power, strength and hypertrophy of global mobilising muscles (Astrand and Rodahl, 1986; Campos et al., 2002). This review did not find any studies comparing overload training principles of the local or global stabilising muscles with low threshold training strategies. Whilst there is reported success of low threshold segmental stabilising programmes (Hubley-Kozey and Vezina, 2002a; Richardson et al., 1999; Sung, 2003) there is still considerable scope for further research to determine if current low threshold strategies are the most efficient form of rehabilitation. Determining whether principles of overload training are appropriate or even beneficial during lumbo-pelvic rehabilitation or injury prevention programmes was not clear from this investigation. No investgative studies were identified that considered the progression from low threshold training to overload strength training. This remains a significant gap in the core stability concept.
The application of research into general muscle strength suggests that the muscle with the largest cross sectional area (CSA) is capable of the greatest force production (Astrand and Rodahl, 1986). If the neural pathway to each muscle is the same then the potential benefit for the muscle with the largest CSA is that it could potentially prevent large excursions of movement beyond the neutral zone due to its capacity to generate an antagonistic force that threatened the neutral alignment of the spine or trunk structures. Another possible benefit could be that the extra muscle bulk simply provides more cushioning and therefore has a dampening effect on direct blows to the body. This review did not find any studies that investigated or addressed these issues.
Muscle function can have an enormous effect on the lumbo-pelvic region (Gibbons and Comerford, 2001a). By either being overactive or tight (shortened) muscles can cause asymmetry around an axis of movement (Comerford and Mottram, 2000). Norris (2000) commented that, “stabiliser muscles tend to ‘weaken’ (sag), whereas mobilisers tend to ‘shorten’ (tighten). Kendall et al. (1983) coined the term ‘stretch weakness’ for stabiliser muscles that maintain their overall normal length however are elongated in their normal resting position. This hypothesis fits in with Panjabi’s (1992b) views on the importance of the deep stabilising muscles maintaining the neutral zone. Studies investigating muscle activation patterns during loading of the thoraco-lumbar region and the preactivation of the local stabilisation muscles of the trunk during upper limb movement support the aforementioned theories (Hodges et al., 2000). The above views are given further substance by the findings of Hodges and Richardson (1996) that transverse abdominus activation enhances efficient muscular stabilisation of the lumbar spine. In contrast, this well constructed case-control study also found poor transverse abdominus muscle activation patterns in back pain subjects.
While there has been significant interest in the importance of the neutral position for the lumbar spine to minimise or prevent back pain (Stott, 2002) less evidence has been purported on the possible influence of asymmetry of the lower limb and the impact of this on the lumbopelvic region. A case study by Cibulka (1999) appeared to indicate that by improving the symmetry at the hip through a programme of stretching and strengthening low back pain was reduced. This study reportedly aimed to decrease lower limb external rotation during the gait cycle and thereby optimise biomechanical forces. This study can only be considered as weak evidence for the benefits of symmetry about the pelvis due to limitations in the study design including sample size and inadequate objective measures.
This review of the evidence found a number of studies that reported positive findings in relation to exercise and back pain (Dolan et al., 2000; Hides et al., 2001; Hodges and Richardson, 1996; Linton and Van Tulder, 2001; Nelson et al., 1999; O’Sullivan et al., 1997; Van Der Velde and Mierau, 2000). There was difficulty in extrapolating meaningful results from some of these studies as they considered a number of variables concurrently that could influence back pain. Dolan et al. (2000) considered a combined programme of aerobic, stretching and strengthening exercises on subjects following a microdiscectomy. The strengthening component described followed core stability training principles however this study design did not make it possible to determine to what extent each of the variables contributed to the improved outcome that was measured by pain and disability. Other limitations of this study were the lack of description in the methodology concerning the specific details of the exercise programme such as frequency, sets and repetitions of exercise. In the study by Hides et al. (2001) the role of specific stabilising exercises for transverse abdominus and multifidus was considered combined with normal medical management and the resumption of normal daily activity. This study provided better evidence for the role of stabilising exercises as the effects of medical management and normal daily activity could be removed from the equation by the control group. Subjects receiving stabilising exercises had better outcomes as measured by recurrence rates.
A number of studies reported no benefit or minimal effect from exercise in improving back pain or posture (Dumas et al., 1995a and 1995b). There were a number of significant limitations from this study including the type of exercise prescribed to the population of pregnant women. The intervention was a general exercise programme based on Canadian guidelines that included aerobic, abdominal strengthening, flexibility and endurance exercises. Specific details of the exercises were not reported in this study however the universal prescription of the same exercises to all pregnant women may have resulted in some receiving inappropriate exercises for their individual states. There was an indication that the lumbar lordotic curve slightly decreased in the exercise group and that with greater lordotic angles higher pain levels were reported.
Systematic reviews on the effects of back pain and exercise provide an indication of general trends however the strength of their evidence is reduced due to their methodology as they are often comparing many different forms of interventions and variables, for example, type of exercise, frequency, duration, intensity and populations. The review by Linton and Van Tulder (2001) suggested that exercise had a mild preventative effect on back pain however was unable to conclude what type of exercise was best. To gain more useful contributions from systematic reviews there would be significant benefit from limiting searches to compare the results from studies that used similar intervention strategies. The term exercise is too generic and limits the opportunity to make specific conclusions and recommendations. An example of a more beneficial study design would be to compare subjects suffering from chronic back pain that have been exposed to the same form of intervention such as low threshold stabilising exercises.
Table 12 highlights the intervention studies used in this guideline. The evidence table associated with the guideline development for Key Question 5 can be seen in Table 18, Appendix G. Checklists associated with the analysis of 3 systematic reviews can be seen following these tables.
|Table 12. Intervention studies for Question 5: Does core stability training decrease the recurrence or extent of lumbo-pelvic dysfunction?