This comprehensive 2013 review summarizes the mechanisms by which exercise training may affect insulin resistance and thus serve as a tool to either prevent or reverse metabolic syndrome. A wide variety of trial and observational evidence has shown that aerobic training increases whole-body insulin sensitivity (i.e., the ability of insulin to clear glucose from the blood) and muscular insulin sensitivity (i.e., the amount of glucose taken up by the muscle in response to insulin). Similarly, sedentary individuals exhibit lower whole-body and muscular insulin sensitivity than active individuals.