Did I get your attention? Good. Can aerobic training really be bad? Yes, if one of your goals is to reduce your bodyfat composition. In the short term it may work because of the calories burned during the aerobic session. But if one of your goals is to drop bodyfat, do you want to do it just for the short term or do you want it for the long term. Repeated aerobic exercise (biking, running, rowing, etc.) teaches your body to become efficient, when actually you want to create inefficiency with each exercise session. This inefficiency will pull energy from different sources (fats, carbohydrates, protein) and force the body to work overtime. And unless you work for the Department of Public Works (sorry if I offended anyone), working overtime produces greater results.