IGNITE is a phase III randomized controlled trial. It is a 12-month, multi-site, randomized dose-response exercise trial in cognitively normal adults between 65-80 years of age. The purpose of this study is to learn whether a 12-month moderate intensity exercise program in older adults can improve cognitive function and brain health. IGNITE will also study whether exercise enlarges certain areas of the brain and what changes in blood biomarkers bring about the improvements. Participants will recieve supervised exercise sessions 3x/week for the 12-month duration of the study.