Exercise, daily physical activity, and age-specific cumulative incidence of mobility decline: an 8-year cohort study of locomotive syndrome

BACKGROUND: Mobility decline is a gradual process that begins earlier than recognized. Locomotive syndrome (LS) captures early mobility impairment using performance tests and a self-reported questionnaire. Although physical activity is important for maintaining mobility, whether simple self-reported exercise habits and daily activity relate to long-term age-specific risk of incident LS has not been fully investigated. This study examined age-specific associations of exercise habits and daily activity with the eight-year cumulative incidence of LS. METHODS: This cohort study included 21,339 Japanese adults aged 21-84 (median, 48) years without LS at baseline who participated in annual health checkups between 2016 and 2024. Baseline exercise habits and daily activity were assessed by self-report using dichotomous questionnaire items, and participants were classified into four groups according to the combination of these responses: inactive (Ex-/Da-), daily activity only (Ex-/Da+), exercise only (Ex+/Da-), and both exercise and daily activity (Ex+/Da+). Analyses were stratified by age (≤ 39, 40-64, ≥ 65 years). Incident LS was defined based on the two-step test, stand-up test, and 25-item Geriatric Locomotive Function Scale. Cumulative incidence was estimated using Kaplan-Meier methods, and associations were assessed with multivariable Cox proportional hazards models adjusted for lifestyle-related factors. RESULTS: Over eight years, 7183 participants developed incident LS. Among adults aged 40-64 years, cumulative LS incidence at 8 years showed a statistically significant decline from 0.45 in the Ex-/Da- group to 0.37 in the Ex+/Da+ group (log-rank P < 0.001), which showed the lowest adjusted risk (hazard ratio, 0.79, 95% CI, 0.72-0.85). A similar statistically significant association was observed in adults aged ≥ 65 years (log-rank P < 0.001), with the lowest adjusted risk in the Ex+/Da+ group (hazard ratio, 0.70, 95% CI, 0.56-0.86). The incidence was higher when LS was defined by the 25-item Geriatric Locomotive Function Scale, suggesting that subjective functional decline precedes performance-based impairment. CONCLUSION: Mobility decline, warranting preventive attention, begins in midlife, not only in older age. Both daily physical activity and exercise were associated with lower long-term risk, and their combination provides the greatest benefit. Subjective functional assessment may represent a useful early intervention target.