Low back pain history and postural sway in unstable sitting.

STUDY DESIGN: A cross-sectional study comparing subjects with self-reported low back pain, recent low back, and no low back pain.

OBJECTIVE: To determine differences in trunk postural control between groups.

SUMMARY OF BACKGROUND DATA: Poor postural control has been demonstrated in patients with low back pain, but the cause of this is unknown.

METHODS: A total of 331 participants of a longitudinal study participated in a seated balancing task. Based on a questionnaire, subjects were subdivided in 3 groups: current-LBP, recent-LBP (last 12 months), no-LBP. Subjects balanced on a seat mounted over a hemisphere during three 30-second trials. Sway amplitudes (RMS), mean power frequency (MPF), short-term diffusion coefficients (DS), and critical point (CP) coordinates of sway were calculated.

RESULTS: RMS values differed significantly between groups, with smaller values in recent-LBP than in no-LBP. MPF values were lowest in current-LBP. DS values were highest in no-LBP, with significant differences between this group and recent-LBP only. CP values were generally lower for recent-LBP than both other groups.

CONCLUSION: In contrast with previous findings, postural sway amplitudes in unstable sitting were not different between LBP and healthy subjects, while subjects with a recent history of LBP showed smaller amplitudes. Higher DS values in subjects without LBP indicated more stochastic sway. These findings may be explained by the disturbing effect of current pain on postural control causing low sway frequencies and by lower effort in balancing in healthy subjects causing high sway amplitudes and diffusion coefficients.