CORE STABILITY

underlying joints in good alignment intrinsically and with respect to surround- ing joints. They can achieve this, without limiting movement, because the muscles cross only one joint (or in the case of the deep MF, only one to two vertebrae).

What happens in the presence of pain? Low back pain has a myriad of causes and is expressed in numerous ways and analysis of aetiology is beyond the scope of this article. However one connecting factor is the alteration in muscle recruit- ment patterns back pain produces.

In a landmark study, Hodges and Richardson (12) showed that in pain free subjects the first muscle recruited to perform the movement of shoulder abduc- tion in a standing position was the TA. In subjects with low back pain there was a delay in contraction and Hodges conclud- ed that “a significant motor control deficit is present in people with chronic low back pain which is primarily associated with the control of contraction of TA”.

The MF muscle is also responsive to back pain. Hides found evidence of wasting of the ipsilateral MF in patients with acute and subacute unilateral pain (13). In a fol- low up study they found that in patients with no intervention, the MF did not return to its original size. Furthermore, with appropriate re-education it did (14).

Additionally, further research taking place at Erasmus University in Holland is indi- cating a link between MF and stability of the sacroiliac joint, as the lower parts of the lumbar MF have an attachment to this joint via the long dorsal sacroiliac (15).

Effects of removing gravity Current research is being conducted on the effects of microgravity and bed rest on stability muscles including TA, MF, the PF, diaphragm and lower limb muscles such as gluteus medius and the vastus medialis oblique (Berlin Bed Rest study, currently underway). The absence of grav- ity results in decreased use and reduced mechanical loading of the muscle system (16) this results in atrophy of the stabil- ising muscles and the conversion of the slow twitch muscle fibres to phasic fast twitch (17), an alteration in characteris- tics from stabilising to mobilising. Further to this, microgravity has no effect on the mobilising muscles.

This effect is due to a characteristic of the nervous system known as neuroplasticity. This is where the physiological structure of muscles is determined by the pattern of neural impulses delivered to it (8). In the case of postural and overuse related prob- lems, if there is a permanent alteration for the worse in the pattern and regulation of muscle activation and use, this may explain why these problems are difficult to overcome. This is a necessary topic of future research.

So how do we reactivate the stability muscles? Research at the University of Queensland in Australia has been the primary force behind this type of retraining, and the team there term it Spinal Segmental Stabilisation, for a full description of this

please refer to their book (8). Practically these muscles need to be activated in a specific, isolated fashion without substitu- tion from the mobilising muscles. An unloaded position is required to achieve this which also enables the subject to direct visual and tactile attention toward the activating muscle to enhance feedback.

The best position initially is usually in crook lying. The subject needs to be told the basis of why they are doing these exercises as compliance is of the utmost importance.

The spine and pelvis should

be in a neutral position, as close to the ‘ideal’ as possible (2).

The diaphragm is an intrinsic part of the core stabilisers so the way the subject breathes is important. Additionally if they are wasting energy and activating accesso- ry muscles of inspiration and forced expira- tion they are not isolating just the core.

A good instruction is to breathe in and as they breathe out to soften and relax the ribcage and gently draw the navel towards the spine. This is the basic activation of the TA. A good contraction can be palpat- ed just anterior and medial to the subject’s anterior superior iliac spine. The muscle should be felt to gently flatten, a bulge indicates that the subject is using their internal obliques.

To activate the PF the instruction can be similar in both sexes, the feeling is of stopping the flow of urine. In men, the

Key points ● Lumbopelvic stability relies on the successful operation of three subsystems, the active (muscle and tendon), the passive (ligament, bone and connective tissue) and the control (nervous system).

● The deep segmental muscles have specific characteristics that separate them from their multijoint counterparts, one of these is the increased ability to produce muscle stiffness, at a level that allows for segmental stabilisation rather than global rigidity. ● Neuroplasticity of the nervous system means that under differing conditions, for example in microgravity or as the result of pain or injury, muscles can alter their characteristics. ● Injury and/or pain has a direct effect on the three subsys- tems and just because the source of pain or injury resolves, it does not necessarily follow that this alteration is reversed. ● Retraining of the lumbopelvic ‘core’ stability muscles, or exercises aimed at restoration of segmental stabilisation, need to be very specific and focused in order to address this deficit.

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