This is an excellent question with a very complex answer. First those who exercise tend to be better educated, more affluent, and not only better genetics but better health habits and any one or more of these may be responsible for the benefit seen in those who exercise. Second the benefits of exercise are real but they are realized in people to differing degrees depending upon your risk of heart disease. Exercise itself has no direct effect on levels of VLDL, TG, LDL, or IDL although exercise does increase HDL and most especially HDL2 which is said to be cardioprotective. The only problem with this universally accepted belief is that no matter how much you exercise the HDL does not typically elevate more than 10% which by itself would not account for the reduction in cardiovascular disease seen in those who exercise. The notion that the heart is a muscle and exercise exercises the heart muscle is not only faulty but the opposite is more correct as athlete s heart is a condition of serious athletes where the heart muscle increases in size to a greater extent than its blood supply grows shortening their life expectancy. There is much more information available but despite what I have said above and for whatever reasons reasonable exercise is always beneficial cosmetically, emotionally, and physically. Good luck.