Physical activity has been suggested to project again brain atrophy, but also to be a determinant of physical activity in older adults. However, research is needed to confirm this bidirectional relationship. Therefore, this research aimed to study the bidirectional relationship between physical activity and brain structure in older adults from the UK Biobank. A total of 3,027 (mean=62.45, SD= 7.27 years old, 51.3% females) had physical activity and MRI data at baseline and follow-up. Physical activity was assessed through a self-reported questionnaire. T1-weighted MRI and diffusion tensor imaging were used to quantify brain volumes and white matter microstructure, respectively. Cross-lagged panel models were performed to estimate bidirectional associations, and linear mixed-effects models (LMM) to investigate the consistency of findings. Overall, our main findings suggest that higher hippocampal volume (Standardized Beta Coefficient=0.075, pFDR<0.001), frontal volume (Standardized Beta Coefficient=0.043, pFDR=0.037), and global fractional anisotropy (Standardized Beta Coefficient=0.042, pFDR=0.028) were associated with more do-it-yourself (DIY) activities (e.g., watering the lawn or digging) levels at follow-up. In addition, strenuous sports at baseline were positively associated with hippocampal volume over time (Standardized Beta Coefficient=0.011, pFDR=0.108). Although this association did not survive/was not significant after adjustment for multiple comparisons, was confirmed by the LMM. In contrast, higher levels of walking for pleasure were negatively associated with white matter volume at follow-up (Standardized Beta Coefficient= -0.026, pFDR=0.008). In conclusion, there is a bidirectional association between physical activity and brain structure in healthy middle-aged and older adults. However, further research is needed to understand why physical activity subdomains are associated differently with brain structures and features during aging.

The authors have declared no competing interest.

MRA received funding from the Ramon Areces Foundation.

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The study used ONLY openly available human data that were originally located at: the UK Biobank data resource for health related research in the public interest. A guide to access is available from the UK Biobank website (http://www.ukbiobank.ac.uk/register-apply/).

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All data analysed herein (including IDPs) were provided by UK Biobank under project reference 68400, subject to a data transfer agreement. Researchers can apply to use the UK Biobank data resource for health related research in the public interest. A guide to access is available from the UK Biobank website (http://www.ukbiobank.ac.uk/register-apply/).