By Kesh Patel, MSc, RNutr, and Dr Suzanne Patel, PhD

In the current realms of rehabilitation, the term 'core stability' has become somewhat of a misnomer. Growing scientific research highlights the impor- tance of 'core endurance' as a more realistic and reliable indicator of long term spinal health. Progressive, low-intensity, muscular endurance training can be used to enhance spinal stability in a functional manner. This can be achieved through accurate manipulation of acute exercise variables in favour of endurance and is key to the effectiveness of spinal stabilisation pro- grammes. This article discusses the role of muscular endurance training to restore and enhance spinal stability, and explores a number of different exer- cise strategies to achieve this.

THE USE OF MUSCULAR

ENDURANCE TRAINING IN SPINAL

STABILISATION

INTRODUCTION The role of muscular endurance training in restoring and enhancing spinal stabilisation is of growing interest from the perspective of back care. Traditionally, spinal stabilisation programmes have focused on increasing trunk muscle strength, however, this has not always been shown to be an accurate predictor of first-time injury (1,2). In fact, several studies have suggested that reduced trunk extensor endurance, and not weakness, is linked to low back prob- lems (2,3,4,5). The logical assumption for spinal stability is that rehabilitation programmes should emphasise endurance as opposed to strength exercises alone.

Within an exercise framework, endurance objectives are commonly met by performing higher repetitions using low loads. In the con- text of spinal stability, this would imply that trunk exercises need to be performed at higher repetitions under reduced load. However, the static, as well as dynamic demands imposed on the spine dur- ing activities of daily living, highlights the potential contribution of isometric endurance training to spinal stability. This suggestion is supported by data showing reduced isometric extensor endurance in individuals with low back disorders (6). The therapeutic chal- lenge resides in selecting and manipulating appropriate exercises to improve stability in preparation for the functional demands of occupation, recreation or performance.

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MEETING ENDURANCE OBJECTIVES Back injury often results from accumulative and repetitive low- intensity (sub-failure) stress, suggesting that endurance training for the trunk musculature may have a role in injury prevention (7). The implication for exercise prescription is that programmes should con- dition the trunk musculature using longer duration and lower effort exercises, in an attempt to simulate the demands of functional activity. This approach seems to be preferable over strength train- ing alone for long term back health (8). This can predominantly be achieved through manipulation of tempo, particularly during the isometric portion of the exercise. Although many dynamic activities have short concentric and eccentric contraction times, more stren- uous tasks may have significantly longer times, with longer isomet- ric requirements. This functional demand can be effectively trained by simply implementing a positional hold at a certain point during an exercise. From a clinical perspective, recent data suggests that isometric holds of the torso musculature of up to 30 seconds pro- duce significant reductions in muscle oxygenation (9), which may have implications in back pathology. With this in mind, isometric holds (where specified) should be no longer than 30 seconds at low levels of muscle co-contraction and no longer than 8-10 seconds at

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