Abstract
BACKGROUND: physical function (PF) and physical activity (PA) both decline as adults age and have been linked to negative outcomes, including dementia, depression and cardiovascular diseases. Although declines in each are associated with numerous negative outcomes, the longitudinal relationship between these two measures is unclear. OBJECTIVE: to examine the dynamic, bidirectional associations between declines in PF and PA. DESIGN: prospective cohort. SETTING: the Monongahela-Youghiogheny Healthy Aging Team (MYHAT) study. SUBJECTS: about 1,404 men and women, 76.96 ± 7.2 years, 62.4% female and 95.2% white. METHODS: over nine annual assessment cycles, PF was evaluated via the timed Up-and-Go task and PA via a self-reported questionnaire. Piecewise latent growth models examined bidirectional associations between PA and PF to determine whether the initial values (intercept) or early slope (cycles 1-5) (in either PF or PA) predicted later slope (cycles 5-9) (in either PF or PA). RESULTS: initial PF significantly predicted early (standardised β= -0.10, P < 0.001) and later (standardised β= -0.09, P = 0.01) PA slopes. Initial PA significantly predicted later (standardised β = -0.09, P = 0.04) but not early PF slope. Associations were independent of baseline memory test scores, baseline cognitive status, later cognitive status and age. Early physical function slope neither predicts later PA slope nor did early PA slope predict later PF slope (both P values >0.10). CONCLUSIONS: the relationship between PF and PA is bidirectional, with PF more consistently predicting declines of PA, both in the short- and long-term. Intervening on PF impairments may improve PA engagement, which could in turn promote PF and translate to beneficial effects on cognitive function, cardiovascular health and mood.