Daily Physical Activity and Functional Disability Incidence in Community-Dwelling Older Adults with Chronic Pain: A Prospective Cohort Study

OBJECTIVE: This study examined the association between daily physical activity and functional disability incidence in community-dwelling older adults with chronic pain. DESIGN: Prospective cohort study. SETTING: Japanese community. SUBJECTS: Of the 5,257 participants enrolled for baseline assessment, data on the 693 participants who had chronic lower back or knee pain and underwent daily physical activity assessment using an accelerometer were analyzed. METHODS: Participants were assessed for regular physical activity (step counts, moderate- to vigorous-intensity physical activity duration, and light-intensity physical activity duration) using an accelerometer at baseline and were followed up for monthly functional disability incidence, based on the national long-term care insurance system, for approximately two years. We determined the effect of physical activity cutoff points on functional disability incidence using receiver operating characteristic curves and Youden index. Cox proportional hazards regression models were used to analyze associations between the cutoff points and disability incidence. RESULTS: Among the 693 participants with chronic pain, 69 (10.0%) developed functional disability during the follow-up period. Participants with lower physical activity levels showed significantly higher risk of disability. After adjusting for all covariates, functional disability was associated with step counts (hazard ratio [HR] = 1.79, 95% confidence interval [CI] = 1.02-3.14) and moderate- to vigorous-intensity physical activity duration (HR = 2.02, 95% CI = 1.16-3.51) but had no relationship with light-intensity physical activity duration (HR = 1.72, 95% CI = 0.97-3.05). CONCLUSIONS: Maintenance of physical activity with at least moderate intensity may be effective in preventing disability even among older adults with chronic pain.