Acute Exercise and the Cerebral Metabolic Response in Aging and Alzheimer's Disease

Aim 1: Compare the effects of acute, moderate intensity and acute, higher intensity exercise on cerebral glucose metabolism in nondemented (ND) elderly and AD subjects. ND (n=30) and AD (n=30) subjects will undergo a single bout of moderate intensity (45-55% HRR) or higher intensity (65-75% HRR) exercise to assess the effect of exercise intensity on acute change in brain glucose metabolism (rest to exercise). Investigators hypothesize that both moderate and high intensity exercise will elicit a drop in global brain glucose metabolism compared to quiet rest, but that the effect will be greater with higher intensity vs. moderate intensity exercise, and greater in ND subjects than in AD subjects. Aim 2: Characterize the effect of both exercise intensities on acute biomarker response and cognition (memory and executive function) in ND and AD subjects. The acute biomarker response to exercise and the effect on cognition has not been examined in aged or AD cohorts. Investigators hypothesize that acute higher intensity exercise will elicit a greater blood lactate response (area under the curve, AUC) compared to acute moderate intensity exercise, and that this response will be greater in ND than in AD subjects. Investigators further hypothesize that lactate AUC will track negatively with change in cerebral glucose metabolism and cognitive performance. Although investigators will focus on lactate, they will also quantify additional exercise-related biomarkers.