The point as I see it isn't whether this is due to previous health condition but if strenuous exercise exacerbates that condition, to the point that you were better off doing moderate exercise instead of running the marathon or doing the century.

Can Exercise Kill?
The answer: Yes, and probably more often than you think
By KEVIN HELLIKER
Staff Reporter of THE WALL STREET JOURNAL
October 11, 2004; Page R7

In the space of seven months in 2002, three physicians at Johns Hopkins Hospital in Baltimore suffered sudden cardiac death while exercising. Two were running, the other working out in the hospital's fitness center. All three had paid close attention to diet and exercised regularly. The oldest was 51.

This unlikely string of deaths brought tremendous local attention to a topic that medicine typically doesn't emphasize -- for good reason.

Exercise, after all, prolongs more lives than it cuts short. And in a nation that is largely sedentary, people need no extra excuse not to exercise.

Yet a growing number of physicians believe that publicizing the risks of exercise could potentially save a significant number of lives. Johns Hopkins cardiologist Nancy Strahan, for one, is now advising her middle-aged patients to stay away from jogging until they've undergone an exam to determine their risks.

"Present research reveals that vigorous exercise is responsible for triggering up to 17%" of sudden cardiac deaths in the U.S., says a recent article in the American Medical Athletic Association Journal. This means that vigorous exercise is triggering tens of thousands of U.S. deaths a year.

Impact on Immune System

What's more, sudden death isn't the only risk. Evidence is mounting that extreme exercise -- marathons, triathlons and the like -- may be detrimental to the immune system and long-term health. "Exercising to excess can harm our health," cautions Kenneth Cooper, the physician credited with founding the aerobics movement back in the 1960s.

All of this, of course, runs counter to conventional wisdom, which says that exercise is a virtue, and that you can't get too much of a virtue.

Indeed, pretty much as soon as a thirtysomething slips on his first pair of running shoes he is challenged by an acquaintance or athletic-store poster to run a marathon. But exercise more accurately may be perceived as a medical therapy, and doctors are generally very cautious about the dosages they prescribe for medical therapies. Nobody would recommend quadrupling the dose of a drug that had proved to be effective.

So, how much is too much? It depends, of course, on the person.

The risk of sudden cardiac death during exercise would be reduced if people -- especially those older than 40 -- underwent various tests before starting a workout program. These tests include: an electrocardiogram, an electrical recording of the heart that can detect various abnormalities; an exercise stress test, during which physicians monitor the cardiovascular system's response during a treadmill workout; and an echocardiogram, an ultrasound scan that can spot a wide range of defects.
Whether your insurance will pay for these tests depends on your age, health plan and how strongly your doctor recommends them.

Although these tests aren't guaranteed to find every cardiovascular booby trap that exercise can trip, they can identify a significant percentage of the conditions that cause sudden cardiac death-artery blockages, cardiac arrhythmias, aneurysms and more.

The risk of sudden death during exercise appears to rise as the duration of the workout grows. For instance, the risk of death during a marathon is about one in 50,000 finishers -- significantly higher than during shorter races or inactivity. One reason is that during long-distance runs the body sustains muscle injury, and it can react to this injury as if it were bleeding, by rendering blood more clottable, says Arthur Siegel, a Harvard University professor and chief of internal medicine at McLean Hospital in Belmont, Mass. In people with hidden blockage in their coronary arteries, this thickened blood can result in sudden cardiac death.

But that's not the only danger. Muscular injury can also set off a hormonal response that in turn triggers water intoxication, with acute brain swelling, says Dr. Siegel. This can be deadly for marathon runners who take too seriously the recommendation to drink lots of fluid. In recent years, young and healthy runners have died of hyponatremia -- essentially drinking too much fluid -- in several marathons, including those in Chicago and Boston.

"A half-million Americans a year are going out to run marathons," says Dr. Siegel. "They incur a dose of exercise that is enough to cause muscle injury that could, under certain circumstances, have grave consequences."

Having run 20 marathons himself, Dr. Siegel calls himself an advocate for safe participation. Avoiding hyponatremia is mostly a matter of drinking only when thirsty, and this caution is especially important for slower runners.

As for sudden cardiac death, Dr. Siegel suggests that people at risk for cardiac disease perhaps should be cautious about pushing their heart rates too high. People with high risk factors "ought to be careful about keeping the intensity moderate," says Dr. Siegel. "Exercise at a level where they can be conversational." Should such people run marathons? Dr. Siegel advises: "Do the marathon training but skip the race."

An increasingly popular theory has it that death from extreme exercise may not come until years afterward. This theory first occurred to Dr. Cooper, founder of the Cooper Institute in Dallas, when he noticed what seemed like a higher-than-average rate of cancer and other disease among the fitness fanatics he knew.

'More Harm Than Good'?

Having now studied the matter for more than 20 years, he has concluded that especially long and intense bouts of exercise may be damaging to the immune system. It is only a theory, but it is at least partly based on medical studies such as one showing that marathoners suffer a high rate of cold and flu just before and after races.

"If you're exercising more than five hours a week [at a high intensity], there's a possibility that you may be doing more harm than good," Dr. Cooper says.

Nobody should feel compelled for health reasons to run marathons, do triathlons or otherwise aspire to become a fitness fanatic, says Dr. Cooper, adding that 30 minutes a day of moderate exercise such as walking is sufficient.

Of course, there are benefits to extreme exercise -- it provides enormous relief from stress and consumes a spectacular number of calories. For people committed to exercising fanatically, Dr. Cooper and others recommend diets heavy in antioxidants such as green vegetables, as well as supplements such as vitamins C and E. Such diets are believed to bolster the immune system.

Devotees of extreme exercise express confidence that any risks, including a possible increased vulnerability to cancer, are outweighed by benefits ranging from lowered blood pressure to heightened confidence. This explains why Frank Webbe, a professor of psychology at Florida Institute of Technology, has run 14 marathons.

"You run them because you can," says Dr. Webbe, a veteran officer of a group called Running Psychologists. Marathons, he says, are "part of my identity. It's a self definition. I'm one of the elite few. It's important to me."