Sex Differences in Age-Related Functional Mobility Decline: A Moderated Mediation Analysis

While functional mobility is known to deteriorate with age, the specific mechanisms driving this decline, along with potential differences between men and women, are not fully established. Therefore, the present study applied a moderated mediation framework to investigate whether lower limb strength and body mass index (BMI) mediate the relationship between aging and functional mobility, and to explore if sex acts as a moderator in these relationships. A cross-sectional design was used to evaluate 408 independent older adults (mean age: 71.9 ± 3.9 years; 273 females and 135 males). Assessments included the Timed Up and Go (TUG) for functional mobility, the 30 s Chair Stand for leg strength, alongside BMI calculations. Direct and indirect pathways were subsequently evaluated using a moderated mediation analysis. Lower limb strength and BMI significantly predicted functional mobility in both sexes (p < 0.05), with no significant moderation in the indirect pathways. Regarding conditional effects, advancing age predicted poorer functional mobility in females (p = 0.008) but not in males (p = 0.141), independent of the mediators. Strength and BMI appear to be correlates of functional mobility. However, since the age-by-sex interaction term was not statistically significant, the potential sex-specific direct effect of age must be interpreted with caution. While these findings hint at possible subtle differences in aging trajectories, future research is needed to confirm whether interventions for older women require addressing factors beyond strength and body composition.