Objective physical activity characteristics and long-term functional disability trajectories in community-dwelling...

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.

Using the National Health and Aging Trends Study (NHATS), we analyzed 480 community-dwelling older adults (weighted N = 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.

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.

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'.