In 1924, famous cardiologist Paul Dudley White claimed that "exercise can’t hurt a healthy heart". Over the years, several poorly-controlled studies have shown that ultra-endurance events, such a running a marathon, might impair heart function. Now a study from Northwestern University shows that Dr. White is still correct (Journal of the American Society of Echocardiography, February 2006). The authors tested 45 patients before they ran the Chicago Marathon and re-tested them one month after the race. They demonstrated that the race had not caused any abnormalities in heart function.
This does not mean that everyone can go out and run a marathon. People who have damaged hearts can die from over- exertion. If you are a middle-aged person who is thinking about starting a vigorous exercise program, you should get a stress test, an electrocardiogram done while you are exercising vigorously. Tests done while a person is at rest often do not pick up blockages in the arteries leading to the heart. If your stress test shows warning signs, you may need further tests. If you pass your stress test, the odds are strong that you can start your exercise program safely. Once you have your doctor's approval, begin your exercise program gradually to build up the strength of your skeletal muscles and your heart over several months. Then you will be ready to start serious training for your marathon or other endurance event.