Alzheimer's Prevention Through Exercise

Inclusion Criteria: * Clinical Dementia Rating 0 (nondemented) * Age 65 or older * Florbetapir PET evidence of cerebral amyloidosis * Sedentary or underactive by the Telephone Assessment of Physical Activity * Stable doses of medications for 30 days. * Clinician judgment regarding subject's health status and likelihood to successfully complete the 1-year exercise intervention Exclusion Criteria: * Clinically significant major psychiatric disorder (e.g., Major Depressive Disorder) according to standard criteria or significant psychiatric symptoms that could impair the completion of the study * Clinically-significant systemic illness that may affect safety or completion of the study * History of clinically-evident stroke * Clinically-significant infection within the last 30 days * Active cardiac condition (e.g. angina, myocardial infarction, atrial fibrillation) or pulmonary condition in the past 2 years that, in the investigator's opinion, could pose a safety risk to the participant-unless cleared for exercise by the participant's primary care physician or cardiologist. * Uncontrolled hypertension within the last 6 months * History of cancer in the last 5 years (except non-metastatic basal or squamous cell carcinoma) * History of drug or alcohol abuse as defined by DSM-IV criteria within the last 2 years * Insulin-dependent diabetes mellitus * Significant pain or musculoskeletal disorder prohibiting participation in an exercise program * Unwillingness to undergo or contraindication to brain MRI scan. * History within the last 5 years of primary or recurrent malignant disease with the exception of resected localized cutaneous squamous cell carcinoma, basal cell carcinoma, cervical carcinoma, or prostate cancer.