Individual joint contributions to forward propulsion are not related to stability during walking in young or older adults

Background: Older adults are less stable and walk slower than younger adults, both of which are associated with higher fall risk. Older adults use ankle musculature less and rely more on hip contributions for forward propulsion than younger adults, which has been suggested to be a protective walking strategy to increase stability. However, whether distal-to-proximal redistribution of propulsion and dynamic margin of stability are related has not been determined. Objectives: To determine whether the distal-to-proximal redistribution of propulsion (redistribution ratio) is related to margin of stability during preferred walking conditions. Methods: 89 participants were classified as either young adults, high functioning older adults, or low functioning older adults. Participants completed walking trials at their preferred walking pace overground. From these trials, anterior-posterior margin of stability and mediolateral margin of stability at heelstrike, midstance, and toe-off, for each gait cycle were computed, alongside a redistribution ratio. Results: Lower functioning older adults exhibited an increased reliance on hip musculature for forward propulsion compared with younger and high-functioning older adults, in addition to greater mediolateral margins of stability. Accounting for group and walking speed, a proximal shift in individual joint contributions to propulsion was associated with increased mediolateral margin of stability at heelstrike, midstance, and toe-off; and not with any changes in anteroposterior margins of stability. Significance: Our results suggest prioritizing mediolateral stability is a potential explanation for, or consequence, of the age- and function-related shift toward proximal joint contributions to forward propulsion during walking.