Characteristics of Unsuccessful Balance Reactive Responses to Lateral Loss of Balance in Older Adults

Introduction: An effective reactive step response to an unexpected balance loss is an important factor that determines if a fall will happen. We investigated reactive step strategies and kinematics of unsuccessful balance recovery responses that ended with falls in older adults. Methods: We compared the strategies and kinematics of reactive stepping after a lateral loss of balance, i.e., perturbations, between 49 older female adults who were able to successfully recover from perturbations (perturbation-related non-fallers, PNFs) and 10 female older adults who failed to recover (perturbation-related fallers, PFs). In addition, we compared the successful versus unsuccessful recovery responses of PFs matched to perturbation magnitude. Results: The kinematics of the first reactive step response were significantly different between PFs and PNFs, i.e., longer initiation time, step time, swing time, and time to peak swing-leg velocity, larger first-step length, and center-of-mass displacement. Incomplete crossover stepping and leg collision were significant causes of falls among PFs. Similar findings were found when we compared the successful versus unsuccessful recovery responses of PFs. Conclusions: The crossover step, which requires a complex coordinated leg movement, resulted in difficulty in controlling and decelerating the moving center of mass following a lateral perturbation, affecting the kinematics of the stepping response, leading to a fall.