Exploring trajectories of physical functioning by transport mode, neighbourhood environment, and self-selection among mid-to-older adults: A multilevel longitudinal study in Brisbane, Australia

Physical functioning is a key determinant of quality of life and healthy ageing in mid-to-older adults; however, little is known about how transport mode and neighbourhood environmental features jointly shape trajectories of physical functioning. Additionally, potential confounding for self-selection bias for living in neighbourhoods that support preferred behaviours has been insufficiently addressed in prior research. Data were drawn from 3,075 participants aged 45–74 years as part of the How Areas in Brisbane Influence healTh and activiTy (HABITAT) longitudinal study conducted in Brisbane, Australia. Multilevel linear regression analyses were used to examine associations between neighbourhood walkability and public transport accessibility accounting for residential self-selection, with changes in self-reported physical functioning across primary transport modes. Results indicated that self-selection weakened the association between active transport users and improvements in physical functioning, rendering it non-significant. Neighbourhood walkability and public transport accessibility were not associated with changes in physical functioning in the fully adjusted model. However, transport mode use moderated the association between neighbourhood features and change in physical functioning. Significant interaction effects indicated that higher residential density, greater street connectivity, higher walkability, and closer proximity to bus stops were associated with greater improvements in physical functioning among public transport users, compared with private transport users. Future studies are needed to interrogate causal pathways accounting for residential self-selection over a longer time frame to better understand how physical functioning changes in relation to diverse travel modes.