Objective physical activity characteristics and long-term functional disability trajectories in community-dwelling older adults: the amplifying risk of stroke

Background: Functional decline is a major challenge in aging, particularly for those with a history of cerebrovascular events. Yet, prior research relies heavily on self-reported measures. The impact of objective physical activity patterns, particularly sedentary accumulation, on long-term functional prognosis remains unclear. Methods: = 1.9 million). Group-Based Trajectory Modeling (GBTM) was applied to 7 years of follow-up data to identify trajectories of ADL disability. Wrist-worn accelerometry captured objective activity profiles. Weighted logistic regression and restricted cubic splines assessed associations between activity metrics and adverse trajectories. Results: Three distinct trajectories were identified: "Robust," "Progressive Decline," and "Persistent Severe Disability." Stroke survivors were disproportionately represented in the severe disability group compared to controls (35% vs. 10%). Although stroke survivors constituted a small proportion of the unweighted sample, they exhibited a profoundly amplified vulnerability to sedentary behaviors. Average sedentary bout length emerged as a core risk factor independent of total activity volume (aOR 1.15 per 10-min increase). Total activity exhibited an "L-shaped" protective association, while sedentary time showed a "J-shaped" risk threshold (>700 min/day). Interaction analysis revealed that frequent interruptions of sedentary time could partially offset the risks associated with low total activity volume. Conclusion: Beyond total activity volume, continuous sedentary patterns are critical biomarkers of functional decline in older adults. Stroke survivors represent a highly vulnerable subpopulation where clinical rehabilitation strategies should prioritize 'sedentary interruption'.