Postural sway and stepping response among working population: reproducibility, long-term stability, and associations...

OBJECTIVE: To investigate the day-to-day reproducibility and long-term (9 months) stability of variables of postural control, and the associations of these variables with low-back and lower-extremity pain in a working population. DESIGN: Test-retest measurements of 18 healthy subjects. Cross-sectional study of 165 working women and 343 men. BACKGROUND: Sudden loss of postural balance may result in microtraumas of back structures. Therefore workers with decreased postural control may run an increased risk of low-back pain. There are few reports describing the reproducibility of force-plate-based posturography. METHODS: Amplitude and velocity of postural sway were measured with a force-plate in a two-feet stance with eyes open and closed, and in a one-foot stance with eyes open. A stepping response test was developed to measure the dynamic components of balance. RESULTS: The mean differences between the repeated measurements were generally 5-10% and the standard deviations of these differences were up to a quarter or one third of the mean measurement values. Sway velocity showed the best overall reproducibility. Men had a larger sway than women independent of age and anthropometry. The group of non-symptomatic subjects showed wide variation and a slightly lower sway than the groups with low-back or lower-extremity pain. CONCLUSIONS: Postural sway has moderate stability, wide variation, and slight associations with low-back symptoms in a working population.