Specific aim 1. Using a fully crossed 2 (intensity) X 2 (duration) design, the investigators will demonstrate a dose-response relationship between volume of aerobic exercise and changes in DNA methylation over four months among previously sedentary women.~Hypothesis 1: The investigators predict that there will be an interaction between intensity and duration characterized by a dose-dependent response to total exercise volume, such that women will experience the greatest improvements in methylation at high intensity/high duration (16.4 kcal/kg/week) and the least improvements in methylation at low intensity/low duration (5.6 kcal/kg/week).~Hypothesis 2: The investigators predict that there will be a main effect of exercise duration, such that women exercising for 40 minutes/session, 4 sessions per week will show more improvement in DNA methylation compared with women exercising for 20 minutes/session, 4 sessions per week.~Hypothesis 3: The investigators predict that there will be a main effect of exercise intensity, such that women exercising at 75% of VO2max will show more improvement in DNA methylation compared with women exercising at 55% of VO2max.~Specific aim 2. There are no published data on the extent to which positive effects of exercise on methylation might decay if exercise is not continued. The investigators will gather data on the natural history of methylation decay after training.~• Hypothesis 4: At six months following the end of supervised exercise, the investigators will assess the influence of the different levels of initial training and the passage of time on DNA methylation, covarying whether or not participants continued to exercise. It is predicted that the highest volume group will show the greatest persistence of positive changes in DNA methylation. Alternatively, it is possible that all four groups will return to baseline methylation levels of methylation, and there will be no difference in methylation at 6 months following the end of supervised exercise.
Specific aim 1. Using a fully crossed 2 (intensity) X 2 (duration) design, the investigators will demonstrate a dose-response relationship between volume of aerobic exercise and changes in DNA methylation over four months among previously sedentary women.~Specific aim 2. There are no published data on the extent to which positive effects of exercise on methylation might decay if exercise is not continued. The investigators will gather data on the natural history of methylation decay after training.