 Animal studies have demonstrated that aerobic exercise EXER is a low-cost, low-risk intervention capable of altering the AD pathological process Adlard 2005, Wu 2008. Randomized controlled trials RCTs of EXER in older adults have also revealed its beneficial effects on AD-relevant measures such as brain glucose metabolism and memoryexecutive function Erickson 2011, Baker 2009. Importantly, a recent evidence review found that of 7 key modifiable risk factors for AD, physical activity had the highest impact on reducing the national prevalence of AD Barnes 2011. However, there are presently no RCTs examining the effects of EXER in middle-aged, asymptomatic individuals at increased risk of AD. This is an important knowledge gap for several reasons. Interventions to halt the AD pathological cascade are more likely to be effective if implemented prior to pervasive neuronal damage Sperling 2011. Secondly, persons with specific risk factors for developing AD such as parental family history FH represent a choice target population for any credible attempts at reducing the growing burden of AD Jarvik 2008. Lastly, a key limitation of prior EXER RCTs is the failure to adequately account for participants physical activity levels outside of the intervention. 