Time- vs. Step-Based Physical Activity Metrics for Disability Incidence in Older Adults

Introduction: The recommended target durations for moderate-to-vigorous physical activity (MVPA) to promote health have been established; however, evidence supporting the use of step counts as a measure of physical activity remains limited. We aimed to compare the predictive ability of MVPA and step counts for incident disability among community-dwelling older adults. Methods: This prospective cohort study included a total of 8664 community-dwelling older adults from a community-based setting. MVPA and step counts were measured using an accelerometer. Disability incidence and mortality rates were prospectively assessed over 60 months. Inverse probability weighting-adjusted receiver operating characteristic curve analysis was used to evaluate the predictive ability of MVPA and step counts for disability incidence, while adjusting for covariates. Results: A total of 1,373 (15.8%) patients developed an incidental disability within 60 months. In the inverse probability weighting analysis based on the covariate model, the areas under the curve for MVPA and step counts were 0.572 (95% CI, 0.542–0.603) and 0.565 (95% CI, 0.537–0.596), respectively. Conclusion: Among community-dwelling older adults, step counts and MVPA showed comparable associations and predictive performance for incident disability after adjustment for background risk factors. Our findings support the use of step counts as a measure of physical activity in this population.