Dose-Response Association Between Accelerometer-Assessed Physical Activity and Incidence of Functional Disability in Older Japanese Adults: A 6-Year Prospective Study

Background: It is unknown whether moderate-to-vigorous physical activity (MVPA) in bouts of <10 minutes protects against disability risks or if only 10 minutes bouts of MVPA is critical. Additionally, it is unclear whether light physical activity (LPA) or its accumulation patterns is associated with functional disability. Methods: A total of 1,678 adults aged >= 65 years and without functional disability at baseline were followed up for 6 years. Functional disability was identified using the database of Japan's Long-term Care Insurance System. Physical activity was measured using a tri-axial accelerometer secured to the waist. Results: Functional disability was identified in 274 participants (16.3%). When examined as quartiles, higher levels of all MVPA measures were dose-dependently associated with lower risk of functional disability. Associations of MVPA in =10 and <10 minutes bouts remained significant in a mutually adjusted model. Neither total LPA nor LPA in bout of >= 10 minutes, but LPA in bouts of <10 minutes was associated with functional disability. Analyses using restricted cubic spline functions showed that associations of all MVPA measures and LPA in bouts of <10 minutes with functional disability were linear (p for nonlinear >.05). The hazard ratios (HRs; 95% confidence interval [CI]) for functional disability per 10 minutes increment of total MVPA and LPA in bout of <10 minutes were 0.86 (0.81-0.92) and 0.96 (0.93-0.99), respectively. Conclusions: Higher MVPA, regardless accumulation patterns, or LPA in bouts of <10 minutes was associated with lower risk of functional disability in a linear dose-response manner in older adults.