1 Department of Physics, Concordia University, Montreal, QC, Canada.
2 Centre EPIC and Research Center, Montreal Heart Institute, Montreal, QC, Canada.
3 School of Health, Concordia University, Montreal, QC, Canada.
4 Department of Biomedical Science, Faculty of Medicine, Université de Montreal, Montreal, QC, Canada.
5 BrainLab, Hurvitz Brain Sciences Research Program, Sunnybrook Research Institute, Toronto, ON, Canada.
6 Dr. Sandra Black Centre for Brain Resilience and Recovery, Sunnybrook Research Institute, Toronto, ON, Canada.
7 Department of Psychology, Concordia University, Montreal, QC, Canada.
8 Department of Medicine, Université de Montreal, Montreal, QC, Canada.
9 Department of Nutrition, Université de Montréal, Montreal, QC, Canada.
10 Research Center, Institut Universitaire de Gériatrie de Montréal, Montreal, QC, Canada.

Aerobic exercise training promotes cardiovascular, brain and cognitive health. Regular exercise is associated with higher cardiorespiratory fitness, commonly assessed by peak oxygen uptake (VO_2peak) during maximal effort testing. Higher cardiorespiratory fitness has been linked to preserved brain health, particularly higher gray matter volume and perfusion. The brain relies heavily on oxidative metabolism, yet the relationship between cardiorespiratory fitness and brain oxidative metabolism remains underexplored. This study investigated the association between VO_2peak and two key cerebral metabolic parameters: the cerebral metabolic rate of oxygen consumption (CMRO₂) and oxygen extraction fraction (OEF), which represents the balance between cerebral blood flow (CBF) and CMRO₂. Thirty-seven healthy adults aged ?50 underwent maximal cardiopulmonary exercise testing for VO_2peak assessment. Neuroimaging included dual calibrated functional MRI (dc-fMRI) and quantitative susceptibility mapping (QSM). Higher VO_2peak correlated positively with higher CBF across whole-brain gray matter but showed no relationship with CMRO₂. Conversely, higher VO_2peak negatively correlated with lower OEF from both dc-fMRI and QSM. These findings suggest that greater cardiorespiratory fitness enhances cerebral perfusion without changing resting metabolic rate in healthy older adults, resulting in a reduced oxygen extraction. These results are consistent with exercise yielding improved vascular-metabolic coupling, which would reduce the likelihood of transient hypoxic episodes.