Pathway from gait speed to incidence of disability and mortality in older adults: A mediating role of physical activity

Objectives: To determine whether physical activity mediates the association of gait speed with incident disability and mortality in older adults. Study design: Prospective cohort data from 782 community-dwelling Japanese older adults were analyzed. The median follow-up periods for incident disability and mortality were 4.4 and 4.5 years, respectively. Main outcome measures: Physical activity was assessed with the Japan Arteriosclerosis Longitudinal Study Physical Activity Questionnaire, gait speed was calculated from 5-m walking time, and incident disability was defined as long-term care insurance certification during follow-up. Results: There were 247 cases of incident disability and 202 deaths during follow-up. After adjusting for potential confounders, faster gait speed was associated with decreased risk of incident disability (hazard ratio [HR] = 0.87, 95% confidence interval [CI] = 0.82-0.93), but physical activity level was not associated with incident disability (HR = 0.98, 95% CI = 0.95-1.01). Gait speed was associated with mortality risk in the model without physical activity (HR = 0.93, 95% CI = 0.88-1.00). When gait speed and physical activity were both included in the model, gait speed was not associated with mortality (HR = 0.95, 95% CI = 0.89-1.02) but physical activity was associated with mortality (HR = 0.95, 95% CI = 0.92-0.99). Physical activity was a mediating factor in the association between gait speed and mortality (Sobel test p = .025). Conclusions: Gait speed is directly associated with incident disability and is indirectly related to mortality through physical activity in older adults.