Risk of Strenuous Activity to the Sedentary Confirmed : Health: Two studies show that couch potatoes are much more likely to suffer heart attacks from sudden vigorous exercise than are those who work out regularly. Findings support long-held belief.

Sedentary people who occasionally undertake strenuous activity have a greatly increased risk of having a heart attack during exertion, according to two studies.

The studies, published in today’s New England Journal of Medicine, confirm a long-held belief that sudden vigorous exercise can be fatal for couch potatoes. And they appear to support the advice that inactive people consult with their doctors before starting any activity.

In one study by U.S. researchers, the risk of having a heart attack among sedentary people was more than 100 times greater during heavy exercise than during lighter activity or none. In the other study, conducted in Germany, the risk was seven times greater.

Both studies found that people who exercise regularly had a much lower risk of having a heart attack during exertion than to those who do not.

“Although regular exercise has important health benefits over the long term, sudden, vigorous exertion by people who are unaccustomed to it can sometimes end in tragedy,” said Dr. Gregory D. Curfman in an editorial accompanying the studies.

The studies refer to the temporary risk period consisting of the time spent exercising and the hour after--a period that, while brief, is thought to be associated with 75,000 heart attacks in the United States each year, resulting in 25,000 deaths.

“About one in 20 heart attacks is actually triggered in this way,” Curfman said in an interview.

In the U.S. study, researchers used two types of detailed analyses to compare 1,228 men and women who had suffered nonfatal heart attacks with similar people who had not had heart attacks. The patients were interviewed about their usual physical activity both before and during the onset of symptoms and in the year preceding the heart attack.

Slightly more than 4% of the patients reported that within an hour before the heart attack they had engaged in heavy exertion, defined as the energy expended in such activities as snow shoveling, slow jogging or sex.

When the data was analyzed to look at the patients’ normal exercise habits, those who were sedentary had a much greater risk of heavy exertion actually triggering a heart attack than did active people. People who exercised less than once a week were 107 times more likely to suffer a heart attack during exertion compared to their usual risk. In contrast, people who exercised five or more times a week were only 2.4 times more likely to have a heart attack during strenuous activity.

In the German study, conducted at the Free University of Berlin, patients who exercised less than four times a week had a 6.9 times greater risk of heart attack during exercise; those who exercised four or more times a week had a 1.3 times greater risk.

Although the findings support the idea that strenuous exertion itself has a role in triggering a heart attack, researchers do not yet understand how this happens.

“What we hope will come out of these studies on triggering is to better understand what links these external stresses, like shoveling snow, and the actual biological event,” said the study’s lead author, Dr. Murray A. Mittleman of Deaconess Hospital in Boston.

“There are some hypotheses on how physical events trigger (heart attacks). But it’s not very well studied at this point. If we could figure out what that link was, we could perhaps figure out how to break the link.”

Although the studies affirm that regular exercise is a good thing, they carry a stiff warning for the sedentary person who is thinking about starting an exercise program.

Only about one in five Americans exercise for at least 30 minutes five or more times a week. About one in four report no leisure-time physical activity. Sedentary lifestyles are most common among people age 65 and older.

Said Dr. Michael Wong, a Los Angeles cardiologist and adviser to the Greater Los Angeles Affiliate of the American Heart Assn.: “I think it would be prudent that people who are over 40 and who have not exercised go to their physician and ask, ‘Is it safe for me?’ And when people begin to exercise they ought to do it within the guidelines of the American Heart Assn. Which means--besides getting checked out by your physician--you have a special warm-up period, an exercise period set at a certain level and a cool-down period.”