| Summary: | It has previously been established that individuals with mild chronic low back pain (CLBP) have a delayed rate of post-exercise stature recovery compared to asymptomatic controls, and that this is associated with increased paraspinal muscle activity, pain and disability. The purpose of this thesis was to explore these relationships further in NHS patients with CLBP and to establish if links exist between these measures and a number of psychological factors known to play an important role in the development of the condition. Forty seven patients were recruited from the waiting list for two physiotherapist-led rehabilitation programmes. Paraspinal muscle activity was assessed via surface EMG while standing at rest and stature recovery over a 40-minute unloading period was measured on a precision stadiometer. Self-report of pain was noted and patients were asked to complete a questionnaire booklet assessing disability, anxiety, depression, pain-related anxiety, fear of movement, self-efficacy, catastrophising and defensiveness. Where possible, patients returned for a second testing session after completing the rehabilitation programme (n = 23) and again after a further six months (n = 14). The effect of superficial heat treatment was additionally assessed via a similar testing session (n = 24), but on this occasion the participant put on a heat wrap two hours before the time of the appointment. Significant correlations were found between baseline muscle activity and both pain and disability. Pain was a significant mediator in the relationship between muscle activity and disability. Muscle activity also demonstrated links with self-efficacy, depression, anxiety, pain-related anxiety and catastrophising and was a significant mediator in the relationship between self-efficacy and pain. Stature recovery was not significantly related to any of the other baseline measures, perhaps reflecting the heterogeneous nature of the patients involved. A high prevalence of defensive high anxious individuals was found in the patient group. Changes in stature recovery immediately following the programme were significantly linked to improvements in pain and disability, although a significant increase in stature recovery was only observed by the end of the follow-up period. Resting EMG was not reduced following the rehabilitation programme. The heat wrap resulted in a significant decrease in non-normalised EMG levels and a positive effect on self-report of disability, self-efficacy, catastrophising and pain-related anxiety. In conclusion, the relationship between stature change and muscle activity appears to be more complex than originally hypothesized. However, six months after a rehabilitation programme, the rate of stature recovery had increased to levels similar to asymptomatic individuals, suggesting that the delayed recovery seen in CLBP patients is not primarily the result of pathology. The findings confirm that muscle activity plays an important role in CLBP, in particular as a pathway by which psychological factors may impact on clinical outcome. The role of muscle activity as a mediator between psychological factors and pain suggests that interventions that are able to reduce muscle activity may be of particular benefit to patients demonstrating characteristics such as low self-efficacy, which may help in the targeting of treatment for CLBP. The results also highlight that an immediate decrease in EMG levels following active treatment may not always be the optimal response for long-term improvements in clinical outcome and that a period of adaptation might be expected. The unexpectedly high prevalence of a defensive high anxious coping style suggests that this may represent a risk factor for CLBP, a predictor of poor outcome or an adaptation to a chronic condition.
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