An evaluation of the longitudinal, bidirectional association between processing speed and self-reported physical...

Previous research shows a complex, bidirectional relationship between cognitive performance and physical functioning in older adults, but the direction and strength over time remain unclear.

This study examined longitudinal association between processing speed and physical function, focusing on which domain more strongly influence the other.

Cross-lagged panel models were estimated using data from waves 4, 5, and 6 of the German Aging Survey, including 2715 middle aged and older participants (aged 40+) living in private households in Germany. Cognitive performance was assessed as processing speed via the Digit Symbol Substitution Test and self-reported physical function via the SF-36 physical functioning subscale Health Survey. The final adjusted model controlled for baseline age, sex, education, depressive symptoms, and chronic disease burden.

The adjusted model showed small bidirectional longitudinal associations between processing speed and physical functioning. Physical functioning predicted later processing speed across both time intervals. Processing speed predicted later physical functioning from T1 to T2, whereas the T2 to T3 association was attenuated to marginal significance after covariate adjustment. Sensitivity analyses supported the overall robustness of these modest associations.

Processing speed and self-reported physical functioning show modest bidirectional longitudinal coupling across later adulthood. These findings highlight the importance of considering cognitive performance and physical functioning together when studying aging-related functional decline, independence, and quality of life.