Functional Base of Support Decreases With Age

Background Poor balance in older persons increases the risk of injurious falls during daily activities. Functional base of support (FBOS), the anterior-posterior proportion of foot length used in maximal sustained forward and backward leaning, tests controlled center of mass movement, a component of balance required in daily activities. The purpose of this study was to examine the relationship between FBOS and age and establish the reliability of this measure. Methods Subjects were 113 community-dwelling men and women, ages 20 to 91. FBOS, measured on a force platform, is the difference between mean center of pressure location during sustained forward and backward leaning, divided by foot length. Forward lean (FL), backward lean (BL), and average sway distance during normal standing (STAND SWAY) and while leaning (FBOS SWAY) were also measured. Results Mean FBOS was .60 +/- .07 in subjects under age 60, and .42 +/- .12 in subjects 60 and older. FBOS remained constant in younger subjects; beyond age 60, FBOS declined about 16% per decade and was more variable. FL and BL also declined with age, remaining 66% and 34% of FBOS, respectively. STAND SWAY and FBOS SWAY were significantly correlated with each other, but not with FBOS. Conclusions FBOS is a reliable measure and is decreased on average in older persons. This decrease is not related to increased sway while standing or leaning. FBOS is a simple force platform test that has potential as a measure of change in this dimension of balance and as a predictor of falls risk in older persons.