Purpose: To determine differences in muscle activity of superfical multifidus (SM) and iliocostalis lumborum (IL) between healthy subjects (H) and those with a past history of low back pain (HB) during unsupported sitting.

Background: Sitting has been implicated in the incidence of low back pain. However conflcting evidence is reported on the effect of sitting on the erector spinae with some studies noting an increase, others a decrease and others no difference in activity (Callaghan and McGill 2001, Jackson et al 2001, Dankaerts et al 2006). Most studies focus on subjects with current low back pain. It is known that following an episode of back pain deficits in muscle activty may persist (Hides et al 2001).

Methods: 20 subjects gave informed consent, 10 in each of the H and HB groups. Surface electromyography data was recorded from M and IL bilaterally over 4 time points over 15 minutes of unsupported ‘usual’ sitting. This data was normalised using MVCs and compared for differences using repeated measures ANOVA.

Results: Descriptive data for iliocostalis lumborum and superficial multifidus are presented respectively.

No significant difference was detected between groups or time points for either muscle (p> 0.05).

Conclusion: This preliminary study suggests that subjects with a history of low back pain and healthy subjects have no difference in muscle activity of SM and IL in unsupported sitting. This suggests that HB subjects have no residual muscular weakness and implies no further muscular rehabilitation is required. Further research with larger samples should be undertaken.