18 International Journal of Therapy and Rehabilitation, January 2011, Vol 18, No 1 Research L ow back pain (LBP) is a health burden (Koes et al, 2006) and a twentieth century health care enigma (Sieben et al, 2005). The incidence and prevalence of LBP has been widely documented (Croft et al, 1998; Campbell and Muncer 2005, Carragee et al, 2006; Cayea et al, 2006; Carreon et al, 2007; BackCare, 2007). Previous studies have investigated different strands of LBP; belief systems (Fullen et al, 2008), muscle pain and its affect on muscle activity and coordination (Graven-Nielson et al, 1997), the effects of manipulation (Assendelft et al, 2003; Bronfort et al, 2004; Ernst, 2007), the effect of loading on the spine (Callaghan Evaluation of trunk acceleration in healthy individuals and those with low back pain et al, 1998), posture (Cholewicki et al, 2000), stabilization exercises (Ferriera et al, 2006) and management of onset (Hagen et al, 2002; Hagen et al, 2005; Gullick, 2008), but advances in knowledge have not made an impact on its prevalence, nor sug- gested a gold standard of intervention. A better understanding of underlying mecha- nisms occurring during an episode of LBP may therefore be useful for the clinical rea- soning process required for effective and efficient intervention. Flexion-extension movement of the trunk is a regular functional movement and is an inte- gral component of the standard assessment protocol used to assess pain and disability Aims: The aim of this study was to investigate trunk acceleration as a measure of performance in both healthy individuals and those with low back pain (LBP). The study explored the difference in behaviour of trunk acceleration during fexion-extension movements between these two groups. This study investigated the test-retest reliability of the Lumbar Motion Monitor (LMM) using a single task protocol. Methods: Trunk acceleration of a group of healthy participants (M = 5, F = 5) and a group of participants with LBP (M = 4, F = 6) was evaluated using the LMM. Two sets of measurements were obtained from participants performing trunk fexion-extension movements for 8 seconds. Each participant had a 10 minute rest period between measures. Data were analysed using a two-way mixed model for an intra-class correlation (ICC) analysis to investigate the reliability of the measure, and a Bland-Altman graph was used to demonstrate the levels of agreement between those repeated measures. Results: The LBP group of participants demonstrated a slower three dimensional performance than the healthy group. The ICC for average sagittal acceleration (0.96, 95% confdence interval (CI) 0.90–0.98) and peak sagittal acceleration (0.89, 95% CI 0.75–0.96) with a 95% limit of agreement for the repeated measures of between -100.64 and +59.84 degrees/s 2 demonstrates the reliability of the measure. The higher ICC and its narrow confdence interval suggest that average rather than peak acceleration is more reliable. Within group measures for both the healthy and LBP groups demonstrated similar reliability for average acceleration (ICC 0.98, 95% CI 0.92–0.99) and for peak acceleration (healthy group ICC 0.94, CI 0.76–0.99; LBP group ICC 0.92, 95% CI 0.67–0.98). Conclusions: Low back pain may reduce trunk acceleration. The LMM may be used to measure trunk acceleration as a descriptor of trunk performance in response to an onset of LBP. However, the Bland- Altman limits suggest that its reliability is dependent upon the harness upon which the LMM is secured remaining in a fxed position. Key words: n acceleration n kinematics n low back pain n lumbar motion monitor Submitted 15 April, sent back for revisions 22 June; accepted for publication following double-blind peer review 31 August 2010 Augustine Aluko, Lorraine DeSouza, Janet Peacock Augustine Aluko is Lecturer in Physiotherapy and PhD student, School of Health Sciences and Social Care, Brunel University; Professor Lorraine DeSouza is Head of School and Professor of Rehabilitation, School of Health Sciences and Social Care, Brunel University, London; and Professor Janet Peacock is Professor, Public Health Sciences & Medical Statistics, University of Southampton, Southampton General Hospital, Southampton, UK Correspondence to: A Aluko E-mail: toks.aluko@ brunel.ac.uk