Changes in Walking Stability at Different Percentages of Preferred Walking Speed in Healthy Young and Older Adults: Insights From Movement Component Analysis.

Walking instability increases the risk of falls and compromises mobility safety. This study aimed to explore the impact of various percentages of preferred walking speed (PWS)-specifically, 40%, 55%, 70%, 85%, 100%, 115%, 130%, and 145%-along with age-related changes, on walking stability during treadmill walking. Kinematic marker data from all walking speed trials were pooled for analysis, involving a total of 26 participants (13 young adults aged 24.7 ± 2.4 years and 13 older adults aged 60.8 ± 6.4 years). These pooled data were then decomposed into various movement components (i.e., movement strategies), known as principal movements (PMs), using principal component analysis (PCA). These PMs, which resemble the phases of a gait cycle, collectively contribute to the accomplishment of the walking task. The participant-specific largest Lyapunov exponent (LyE) was employed to assess the local dynamic stability of individual PMs, with lower LyE values indicating higher stability, thereby allowing for the examination of walking speed and age effects. The main findings revealed that only the effects of altered walking speeds were observed; specifically, the LyE value for the midstance phase (PM) at 100% of PWS was significantly lower than at 40% of PWS (=0.001), and there was a trend indicating that the LyE value at 100% of PWS was also lower than at 140% of PWS (=0.027). These results suggest that PWS enhances the stability of the mid-stance-phase movement component of the gait cycle more than the slower and faster walking speeds during treadmill walking.