Differential relationships between cardiorespiratory fitness and cortical thickness across the adult lifespan: A generalized additive model approach

Abstract INTRODUCTION Modifiable lifestyle variables, such as cardiorespiratory fitness, may attenuate age‐related brain atrophy. Although recent studies have investigated the relationship between cardiorespiratory fitness and cortical thickness across the adult lifespan, to our knowledge, none have considered nonlinear relationships with age. The current cross‐sectional study explored the nonlinear effects of age on the relationship between cardiorespiratory fitness and cortical thickness across the adult lifespan. METHODS Young, middle‐aged, and older adults ( n = 159; age range = 18–86 years, mean age = 54.2 years) were selected from the Fitness, Aging, Stress, and TBI Exposure Repository (FASTER; Hayes & Hayes). Cardiorespiratory fitness (VO 2 peak) was assessed via progressive maximal exercise testing on a stationary bike. T 1 ‐ and T 2 ‐weighted magnetic resonance imaging (MRI) scans were processed and analyzed using FreeSurfer. Surface‐based analyses were used to identify regions showing a main effect of VO 2 peak on cortical thickness in older adults (55+ years). Average cortical thickness was extracted from regions of interest, and Generalized additive models (GAMs) were used to identify the optimal relationship between continuous age and VO 2 peak on cortical thickness. RESULTS Positive and negative associations between VO 2 peak and cortical thickness were observed in older adults. GAMs demonstrated effects with varying linearity and showed an Age × VO 2 peak interaction in the left superior temporal gyrus, parahippocampal cortex, superior parietal lobe, and inferior parietal lobe, and the right pars orbitalis and lateral orbitofrontal cortex. The relationship between VO 2 peak and cortical thickness became more positive in older adults, but it varied and was nonlinear across age. DISCUSSION These findings highlight the complex relationship between cardiorespiratory fitness and cortical thickness across the adult lifespan. Among older adults, cardiorespiratory fitness may be an important variable contributing to higher cortical thickness in aging.