Gabe Mirkin, M.D.
An article in Physician and Sportsmedicine shows that when an athlete passes out at the end of a race, he usually dos not have a condition that can harm him, but when an athlete passes out during a race, he is more likely to have a serious condition.
Exercise-associated collapse is the most common reason that athletes are treated in the medical tent following an endurance event. It is caused by the loss of muscle pumping action caused by suddenly stopping exercising. When you exercise, your leg muscles squeeze the veins near them to pump blood through your body. Stopping suddenly doesn't allow enough time for your heart to pick up the extra work done by your legs, so your blood pressure drops and you pass out. That's why in a race,you should cool down before you stop. On the other hand, when a person passes out during a race, it often is caused by a heart attack or heat stroke.