During aging, vascular declines occur causing cerebral atrophy, and functional deteriorations. When this decline is faster than the expected age-related decline, a heightened risk of developing dementia can occur. Understanding what risk factors contribute most to cerebral health across the lifespan prior to the onset of vascular changes is of upmost importance. Potential mediators of the aging vascular system include non-modifiable outcomes such as sex, and modifiable factors like physical activity level (PA) and body mass index (BMI). 
This thesis includes one systematic review and three original studies investigating the effectiveness of PA to enhance cerebral health. In manuscript one we conducted a systematic review of cognitive or exercise interventions in healthy older adults that collected magnetic resonance imaging (MRI) scans. We identified that cognitive training was associated with white matter microstructure improvements, exercise training with macrostructural enhancements, and both demonstrated changes to the blood oxygen level dependent signal, indicating changes to hemodynamics, neuronal resources, or efficiency. However, the underlying mechanisms for enhanced cerebral health were unclear given the heterogeneity of interventions, measurements, and samples in terms of age and health status. In manuscript two, we investigated very healthy older adults with no underlying comorbidities comprehend the relationship between cardiovascular fitness and cerebral hemodynamics. We revealed paradoxical findings of greater cardiovascular fitness associated with decreased cerebrovascular reactivity, but preserved structure. In a normal aging sample, the relationship between sex, BMI, PA, and structural outcomes was examined. Females with greater BMI had enhanced structural outcomes, and regardless of BMI, higher PA was beneficial to cerebral health. In contrast, overweight males had the greatest volumetrics and PA did not have much influence on these relationships. The final manuscript incorporated a larger age range of individuals, showing an overall beneficial effect of PA on cerebral blood flow (CBF), but males and females demonstrated unique relationships with CBF, and the intensity of PA reported, which was further influenced by whether they were middle aged or older. 
Therefore, our studies contribute to our understanding of the beneficial effects of PA on brain health, and how these effects are influenced by sex, age, and obesity.