The specific aims for the study will be to determine if aerobic exercise enhances cognition for older adults who are at risk for developing type II diabetes mellitus (T2DM), and to evaluate whether change in insulin sensitivity predicts cognitive performance for subjects randomized to the aerobic exercise group. Sedentary older adults diagnosed with impaired glucose tolerance using an oral glucose tolerance test will participate in a 6-month supervised protocol of either aerobic exercise or stretching. Cognitive testing and blood collection will occur at baseline, and months 3 and 6. Before and after the 6-month intervention, insulin sensitivity, maximum aerobic capacity, and body fat composition and distribution (via CT scan) will be assessed for all subjects. The results of this study may provide support for a relatively simple and inexpensive treatment strategy that specifically targets many of the health factors that directly influence risk of cognitive decline associated with T2DM for older adults.