High intramyocellular lipid (IMCL) content in skeletal muscle has been correlated to insulin resistance in obese subjects. Yet, endurance athletes have high intramyocellular lipid content and very low insulin resistance. There are several explanations for this paradox. This study will use a new magnetic resonance imaging technique to look at the amount of fat in the muscle and its depletion with exercise. We hypothesize that overweight subjects will have higher amounts of fat and deplete this fat more slowly than lean subjects.