How Older Adults Maintain Lateral Balance While Walking on Narrowing Paths

Abstract

BackgroundOlder adults have difficulty maintaining side-to-side balance while navigating daily environments. Losing balance in such circumstances can lead to falls. We need to better understand how older adults adapt lateral balance to navigate environment-imposed task constraints. Research QuestionHow do older adults adjust mediolateral balance while walking along continually-narrowing paths, and what are the stability implications of these adjustments? MethodsEighteen older (71.6{+/-}6.0 years) and twenty younger (21.7{+/-}2.6 years) healthy adults traversed 25m-long paths that gradually narrowed from 45cm to 5cm. Participants switched onto an adjacent path when they chose. We quantified participants lateral center-of-mass dynamics and lateral Margins of Stability (MoSL) as paths narrowed. We quantified lateral Probability of Instability (PoIL) as the cumulative probability that participants would take a laterally unstable (MoSL<0) step as they walked. We also extracted these outcomes where participants switched paths. ResultsAs paths narrowed, all participants exhibited progressively smaller average MoSL and increasingly larger PoIL. However, their MoSL variability was largest at both the narrowest and widest path sections. Older adults exhibited consistently both larger average and more variable MoSL across path widths. Taken into account together, these resulted in either comparable or somewhat larger PoIL as paths narrowed. Older adults left the narrowing paths sooner, on average, than younger. As they did so, older adults exhibited significantly larger average and more variable MoSL, but somewhat smaller PoIL than younger. SignificanceOur results directly challenge the predominant interpretation that larger average MoSL as indicating "greater stability", which we argue is inconsistent with the principles underlying its derivation. In contrast, analyzing step-to-step gait dynamics, together with estimating PoIL allows one to properly quantify instability risk. Furthermore, the adaptive strategies uncovered using these methods suggest potential targets for future interventions to reduce falls in older adults.