Individuals with low back pain (LBP) often exhibit elevated paraspinal muscle activity compared to asymptomatic controls during static postures such as standing. This hyperactivity has been associated with a delayed rate of stature recovery in individuals with mild LBP. This study aimed to explore this association further in a more clinically relevant population of NHS patients with LBP and to investigate if relationships exist with a number of psychological factors. Forty seven patients were recruited from waiting lists for physiotherapist-led rehabilitation programmes. Paraspinal muscle activity while standing was assessed via surface electromyogram (EMG) and stature recovery over a 40-min unloading period was measured on a precision stadiometer. Self-report of pain, disability, anxiety, depression, pain-related anxiety, fear of movement, self-efficacy and catastrophising were recorded. Correlations were found between muscle activity and both pain (r=0.48) and disability (r=0.43). Muscle activity was also correlated with self-efficacy (r=-0.45), depression (r=0.33), anxiety (r=0.31), pain-related anxiety (r=0.29) and catastrophising (r=0.29) and was a mediator between self-efficacy and pain. Pain was a mediator in the relationship between muscle activity and disability. Stature recovery was not found to be related to pain, disability, muscle activity or any of the psychological factors. The findings confirm the importance of muscle activity within LBP, in particular as a pathway by which psychological factors may impact on clinical outcome. The mediating role of muscle activity between psychological factors and pain suggests that interventions that are able to reduce muscle tension may be of particular benefit to patients demonstrating such characteristics, which may help in the targeting of treatment for LBP.
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