Abstract
Functional base of support (FBOS), the effective area for center of pressure (COP) movement, decreases with aging, which would reduce one's ability to restore balance during perturbed stance. We investigated the relationship between ankle muscle strength and FBOS as well as the threshold perturbation acceleration that required a heel-rise (HR) or step (STEP) to maintain balance. Standing posture of 16 young and 16 elderly adults was perturbed with a backward support surface translation with the speed ranging from 15 to 70 cm/s. Dorsiflexor (DF) strength was found to significantly correlate with FBOS measures and threshold acceleration for HR. Significant correlations were also found between FBOS measures and threshold accelerations for HR and STEP, except for the backward FBOS and threshold acceleration for STEP. Elderly subjects demonstrated significantly smaller DF strength and FBOS measures than young subjects, but no significant group difference was detected in plantarflexor (PF) strength. Most elderly subjects took a step once they raised their heels, while most young subjects were able to restore balance after heel-rise. These findings, taken together, imply that weakness in ankle dorsiflexors could limit the ability of elderly adults to restore balance while standing on their toes. FBOS measures and ankle dorsiflexor strength could be sensitive measures to detect individuals with declined balance control.