Elsevier

Manual Therapy

Volume 17, Issue 1, February 2012, Pages 27-33
Manual Therapy

Original article
The relationships between measures of stature recovery, muscle activity and psychological factors in patients with chronic low back pain

https://doi.org/10.1016/j.math.2011.08.001Get rights and content

Abstract

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.

Introduction

Patients with low back pain (LBP) often demonstrate altered muscle function compared to asymptomatic controls. In particular, individuals with LBP have been found to exhibit hyperactivity of the superficial paraspinal muscles during static postures such as standing (e.g. Ambroz et al., 2000).

The height of intervertebral discs changes in response to compressive forces (due to a combination of fluid flow and elastic deformation) and this is reflected in changes in stature. Stature change is therefore used as a proxy measure of the load on the spine and measurements have been shown to correlate with more direct measurements of changes in lumbar spine length assessed via Magnetic Resonance Imaging (MRI) (Lewis and Fowler, 2009). It has also been shown that both chronic low back pain (CLBP) patients and asymptomatic individuals are able to produce stature measurements with a good level of repeatability (Healey et al., 2005b). Healey et al. (2005a) found significantly reduced stature recovery in individuals with mild LBP compared to controls, with stature recovery negatively correlated with paraspinal muscle activity. The authors hypothesized that the elevated muscle activity observed in the LBP group resulted in greater compressive loads on the spine that, in turn, prevented the intervertebral discs from regaining their initial height and consequently prolonged stature recovery. Reduced stature recovery may increase the risk of future back pain and increase loading on spinal structures such as the facet joints (Adams et al., 2002). Significant negative correlations between stature recovery and both pain and disability appear to support the clinical relevance of this relationship (Healey et al., 2005a).

Psychological factors are known to play an important role in LBP and are sometimes viewed as ‘obstacles to recovery’ (e.g. Foster et al., 2010). It has been suggested that one of the ways psychological factors may affect the condition is via increased spinal loading resulting from altered paraspinal muscle activity. Furthermore, LBP patients with high levels of pain-related fear generally exhibit elevated paraspinal muscle activity compared to low fearful patients (Vlaeyen et al., 1999), especially when confronted with movements which they believe to be harmful (Vlaeyen and Linton, 2000). It is proposed that pain-related fear may perpetuate pain and disability via this muscle guarding. Muscle activity may therefore be a contributory factor in the link between psychological factors and clinical outcome.

The study carried out by Healey et al. (2005a) involved individuals who all self-managed their pain. The aim of this study was to extend those findings by analysing the relationship between stature recovery, muscle activity, pain and disability in a more clinically relevant population of NHS patients with LBP, including individuals with more severe back pain than previously examined. In addition, this study sought to establish whether a range of self-report psychological factors are associated with muscle activity or stature change. An asymptomatic control group was included in the design to enable comparison between the two groups. It was hypothesized that, consistent with the findings of Healey et al. (2005a), the patients with LBP would have higher muscle activity and reduced stature recovery compared to the asymptomatic group and that stature recovery would be negatively related to each of muscle activity, pain and disability. Based on the limited previous research in the area, it was expected that muscle activity would be correlated with the psychological factors considered. It was expected that these psychological factors may impact on stature recovery via their influence on muscle activity and hence also lead to observed correlations with stature change.

Section snippets

Participants

Data were collected from 47 patients with LBP (age, 46.2 ± 11.1 yr; height, 166.4 ± 7.5 cm; body mass, 79.3 ± 18.8 kg) who had been referred to a physiotherapist-led rehabilitation programme in North Manchester and 18 asymptomatic controls (age, 44.6 ± 13.3 yr; height, 169.0 ± 10.3 cm; body mass, 70.8 ± 12.7 kg). The LBP group was mixed (18 men, 29 women), between the ages of 23 and 70 years.

Patients on the waiting list for the rehabilitation programme were sent information regarding the study through the post

Results

The mean duration of pain was 7.2 years (range: 3 months to 40 years). Forty two patients and 15 asymptomatic participants completed the questionnaires. Of these, 19 patients (45%) were classed as moderately disabled (RDQ: 9–16) and 11 (26%) as severely disabled (RDQ: 17–24), with classifications based on the work by Stratford et al. (1998). Technical problems with the EMG system at the start of the study meant that EMG data were not recorded for three patients. In addition, one patient was

Discussion

In line with previous research, there was a trend for patients with LBP to have higher muscle activity and delayed stature recovery compared to asymptomatic individuals, although this was not significant when comparing to a matched control group, and the effect size of 0.42 for the comparison of muscle activity (0.71 for the comparison with the total, unmatched, patient group) was less than the average effect size of 1.14 during standing reported in a recent meta-analysis of 20 studies (Geisser

Conclusions

Patients who demonstrated higher paraspinal muscle activity were those with more severe CLBP and the mediational analysis also indicated that muscle activity may affect disability via its influence on pain. The results therefore support the clinical relevance of this measure and suggest that treatments that reduce muscle activity may improve outcome. In addition, muscle activity was significantly correlated with a number of psychological factors and was found to act as a partial mediator

Acknowledgements

The authors wish to thank both the patients and the staff at the physiotherapy department at North Manchester General Hospital where the data collection took place.

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