Resting cerebral blood flow (CBF) and cerebrovasculature responsiveness (CVR) are becoming key measures of brain health. However, traditionally accepted CBF/CVR changes with age/fitness have been recently questioned using a variety of imaging modalities. Here we investigate the source of these discrepancies, performing Doppler and MRI measures on the same groups. We find similar changes in CBF but opposing changes in CVR measures between groups. There was no significant correlation of CBF MRI and Doppler measures across the cohort. Our work shows the necessity to further understand driving factors of CBF/CVR across modalities before use as a clinical research tool.