Age-related changes in mediolateral stability control during walking

Background: Younger adults (YA) may primarily regulate mediolateral stability during walking through proactive control of net ground reaction force orientation, with residual instability during challenging gait conditions mediated by reactive force generation later in the gait cycle. We sought to understand if older adults (OA) use a similar reactive strategy to regulate mediolateral stability during walking when proactive control is limited. Research question: Do gait velocity and step width constraints differentially alter mediolateral gait stability control among healthy younger (18-35) and older (>65) participants? Methods: 28 YA and 28 OA performed normal (NW), fast (FW) and narrow base (NBW) walking conditions across an instrumented walkway. Mediolateral stability was quantified by the minimum mediolateral margin of stability (MoSML). The frontal-plane eccentricity of the GRFnet was calculated at two peaks (P1 and P2) following footcontact. Age- and task-related differences in the magnitude and timing of kinematic and kinetic outcome variables were examined. Results: OA exhibited reduced minimum MoSML, alongside reductions in the P2 eccentricity in both NW and FW conditions. No age-related differences in MoSML were observed during NBW, although OA exhibited a significantly increased P2 magnitude, which was delayed within the gait cycle. No age-related differences in P1 magnitude or timing were noted, nor were there age-related differences in MoSML at the onset of double support. Significance: OA may regulate mediolateral stability through foot-placement, when possible. With constraints on foot placement, OA are able to compensate by generating a sufficient, but delayed, P2 eccentricity to counter instability arising during double support.