Background: Back pain is a common complaint in the Western World with a sedentary lifestyle contributing to its recurrence. The aim of this study was to establish differences in lumbar and thoracic posture after a period of unsupported sitting between subjects with a history of back pain but no current symptoms (BP) and those without a history of back pain (NBP).

Method: Twenty subjects (10 BP and 10 NBP group) fulfilling specific inclusion criteria were recruited. Ethical approval was obtained from the Institutions Ethical Committee. Following placement of markers on the vertebrae L5, T12 and C7, subjects sat unsupported on a plinth following standardisation of hip and knee position. A digital image (sagittal view) was taken at 1, 5 and 10 minutes. Spinal curvature was measured using Matlab, two-dimensional analysis system. Repeated measures ANOVA with Post Hoc analysis were calculated to determine the differences between groups and time points.

Results: The NBP group demonstrated no difference in thoracic or lumbar curvature at 1, 5 and 10 minutes. The BP group showed a statistically significant difference in lumbar spine curvature between one and ten minutes (p=0.006). No significant differences in thoracic curvature in BP group were found (F =.524 p = 0.601).

Conclusion: This study showed that subjects with BP demonstrate a change in lumbar curvature following a period of unsupported sitting compared to NBP group. The thoracic kyphosis in both group remained unchanged. Further studies investigating differences in spinal curvature between specific sub-sets of LBP population could provide useful information on sitting postures.