['Despite mounting evidence that physical activity has positive benefits for brain and cognitive health, there has been little characterization of the relationship between cardiorespiratory (CR) fitness and cognition-associated brain activity as measured by functional magnetic resonance imaging (fMRI). The lack of evidence is particularly glaring for diseases such as Alzheimer disease (AD) that degrade cognitive and functional performance.', 'The aim of this study was to describe the relationship between regional brain activity during cognitive tasks and CR fitness level in people with and without AD.', 'A case-control, single-observation study design was used.', 'Thirty-four individuals (18 without dementia and 16 in the earliest stages of AD) completed maximal exercise testing and performed a Stroop task during fMRI.', 'Cardiorespiratory fitness was inversely associated with anterior cingulate activity in the participants without dementia (r=-.48, P=.05) and unassociated with activation in those with AD (P>.7). Weak associations of CR fitness and middle frontal cortex were noted.'] Does alzheimer disease alter the relationship of cardiorespiratory fitness with brain activity during the stroop task?