The predictive power of brain-predicted age and leg strength on mobility decline in aging: findings from the Baltimore Longitudinal Study of Aging.

Muscle weakness and poor brain health both contribute to mobility limitations in older adults, but their respective contributions and interactions are not well understood. This study examines the relationship between magnetic resonance imaging-estimated brain-predicted age difference (brain-predicted age-chronological age), leg strength, and their interaction on mobility decline using Baltimore Longitudinal Study of Aging data (N = 645, 78.1 ± 7.54 years, 56% women). Partial Spearman correlations evaluated the relationships between leg strength, brain-predicted age difference (BPAD), gait speed, and time to complete 5 repeated chair stands (5CS). Mixed-effects linear regression models examined associations of baseline BPAD, leg strength, and lifestyle factors with mobility change over time (5.74 ± 2.87 years). Logistic regression modeled predictors of success in a narrow course walking task. Leg strength significantly correlated with gait speed (r = 0.26, p < .001) and 5CS (r = -0.27, p < .001). BPAD was associated with decreased gait speed (β = -0.022, p = .011) and slower 5CS (β = 0.331, p = .012). Greater leg strength was associated with preserved gait speed (β = 0.023, p = .022) and faster 5CS (β = -0.552, p < .001). BPAD (OR = 0.712, 95% CI, 0.687-0.940) and leg strength (OR = 0.805, 95% CI, 0.696-0.964) predicted lower likelihood of narrow walk success. Interactions between BPAD and leg strength were not significant for any measure. These findings suggest accelerated brain aging and leg weakness independently contribute to mobility decline, highlighting the need for interventions targeting brain health and muscle strength to preserve mobility in aging populations.