Hypothesis: The investigators hypothesize that exercise training implemented 4-5 times/week for 2 yrs in sedentary middle aged men and women (45-64yr) will improve cardiac and vascular compliance to a degree equivalent to life-long exercisers (and sedentary young). The investigators will perform invasive and non-invasive assessment of cardiovascular structure and function before and after an exercise program involving high intensity aerobic intervals, lower intensity endurance ("base training"), and strength training.