Dual group-based trajectories of physical activity and cognitive function in aged over 55: a nationally representative cohort study.

Background: As individuals age, they commonly experience reduced physical activity and cognitive decline. While evidence, there is limited trajectory research on their concurrent progression and interrelation in individuals over 55 years old. Methods: The data was collected from 5,765 individuals aged over 55 years who participated in the China Health and Retirement Longitudinal Study (CHARLS) between 2011 and 2020. Physical activity was measured by IPAQ, cognitive function by episodic memory, and mental intactness score. Separate sets of group-based trajectory models were fitted to identify physical activity trajectories and cognitive function trajectories. Multivariate logistic regression was used to estimate the association between baseline characteristics and each set of trajectories. Group-based dual trajectory modeling (GBDTM) was applied to quantify these associations. Results: GBDTM identified three distinct trajectory groups for physical activity and cognitive outcomes. The physical activity trajectories were classified as "Persistently low physical activity" (74.2%), "Decreasing physical activity" (13.7%), and "Rising physical activity" (12.1%). Similarly, cognitive function trajectories were categorized as "Persistently low cognitive function" (22.2%), "Persistently moderate cognitive function" (37.9%), and "Persistently high cognitive function" (39.9%). Notably, 15.6% of participants followed the trajectories of "Persistently low physical activity" and "Persistently low cognitive function." The presence of a severe decline in physical activity was associated with an increased likelihood of poor cognitive function and vice versa. Age, sex, education, residential status, BMI, and visual impairment were identified as significant predictors for physical activity and cognitive decline. Conclusion: This study found that the GBDTM can determine the consistent trajectories of physical activity and cognitive function trajectories that persistently decline in individuals over 55 years. Analyses of predictive factors can be instrumental in promoting physical activity and delaying cognitive decline.