The purpose of this research study is to examine the effects of high and low intensity exercise for those with mild memory loss and pre-diabetes. The investigators will also examine the effects of this exercise on certain proteins and hormones in body fluids, and on brain structure and function using magnetic resonance imaging (MRI). Recent studies indicate that exercise improves memory and thinking abilities for adults with mild memory loss OR pre-diabetes. This study examines the effects of exercise on people with mild memory loss AND pre-diabetes.