Effect of stance on test-retest repeatability of biomechanical force platform measures of balance

Objective: Biomechanical force platform measures of static balance have been used to predict falls and monitor responsiveness to drugs in the elderly. The purpose of this study was to determine the effect of stance on test re-test repeatability of force platform measures of balance. Subjects: A convenience sample of 50 subjects was recruited. Ages ranged from 22-84 yrs. 44% of the sample were women. Methods: Wearing the same shoes each time, subjects had their elliptical areas (EA, cm<^2<) and velocity (V, cm/s) of sway measured using an AMTI OR6-3 force platform. Three measurements (10 sec) were made with eyes open in five different stances at least 1 day apart: feet together (FT), feet 30 cm apart (30 cm), feet 70 cm apart (70 cm), comfort stance (CS) and single leg (SL). Results: Pearson correlation coefficients (r) and corresponding p-values for time 1 and time 2 measures are tabulated below: Stance FT 30 cm 70 cm CS SL EA 0.60, p<0.01 0.40, p=0.01 0.44, p=0.01 0.35, p=0.05 0.68, p<0.01 V 0.83 p<0.01 0.74, p<0.01 0.59, p<0.01 0.55, p<0.01 0.89, p<0.01 Conclusion: For all stances, V is more repeatable than EA, because of less within subject variability. Stances that increase between subject variability (FT, SL) are more repeatable than measures made in stances where the subjects are most stable (30 cm, 70 cm, CS).