Defining the concept of physical resilience and quantifying recovery during standing balance in middle-aged and older adults

Physical resilience is the ability to recover from an external perturbation, an integral aspect of functional adaptability and healthy behavior. Techniques that quantify behavior over multiple time scales offer a solution to quantifying resilience. As people age, they tend to lose functional adaptability and resilience. However, age-related declines in resilience between middle-aged and older adults is unclear. This study compared the difference in the ability to recover to baseline following standing balance perturbations between middle-aged and older adults, and between those that do or do not recover to baseline. Thirty-eight middle-aged and thirty-one older adults stood on a force platform during five, 60-sec trials. The platform moved posteriorly a specified distance during each trial (2.54 to 12.7 cm). Detrended fluctuation analysis (DFA) was calculated on anteroposterior center of pressure with moving windows of five seconds. Baseline DFA alpha (BA) was obtained by averaging windows before the perturbation. Directly after the perturbation, windows were analyzed until the DFA recovered within a set criterion of BA, called recovery Alpha (RA). If DFA didn't meet the criterion, DFA of the last window was taken as the RA. Trials were coded as recovery and non-recovery. There was a significant interaction between age and Recover or No recovery on RA. Older adult non-recoverers had a significantly lower RA than middle-aged adults and older adult recoverers. Older adults who did not recover to baseline exhibited less persistent sway, evidenced by decreases in RA. Older adult non-recoverers demonstrating decreased DFA indicates decreased resilience.