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Hard exercise can be risky for the heart, but not doing it is much riskier Add to ...

Alex Hutchinson draws on the latest research to answer your fitness and workout questions

in this biweekly column on the science of sport. The question

Does vigorous exercise

increase my chance of

a heart attack?

The answer

Danny Kassap was one of the fittest people in the world when he was felled by a heart attack early in the Berlin Marathon in September. The 26-year-old Canadian marathon star survived - thanks to rapid intervention by a spectator - but such news inevitably makes us wonder whether we're tempting fate each time we lace up our trainers, and whether we can somehow measure and reduce that risk.

The heads of Russia's Kontinental Hockey League, which was shaken by the sudden death of 19-year-old Alexei Cherepanov last month, seem to think so. In response to the tragedy, which may have resulted from a pre-existing heart condition, they've mandated "in-depth medical examinations" for young players currently in the league, and compulsory exams for all players in the league's next junior draft.

But it's not clear that such preventive measures can make much difference.

There's no doubt that during exercise your risk of a potentially fatal "cardiac event" is elevated, says Paul Thompson, a cardiologist at Hartford Hospital in Connecticut and a leading researcher on the topic. However, it's equally well established that any risks you incur during an hour of exercise are dwarfed by the reduced risk of a heart attack - as much as 50 per cent lower, according to the American Heart Association - during the other 23 hours of the day.

The problem is that the man-bites-dog nature of rare events, like the death of a young athlete, sticks in the mind. "These events really do have a chilling effect on people's desire to exercise," says University of Toronto epidemiologist Donald Redelmeier.

To put the risks into context, Dr. Redelmeier and a colleague analyzed marathon results from more than three million runners. They found that, on average, two deaths occur for every one million hours of aerobic exercise - a rate that isn't significantly different from the baseline hourly risk of being alive for the average 45-year-old man.

The study, published last year in the British Medical Journal, also found that when cities close roads for a marathon, the chance that a traffic death will be averted is nearly twice as high as the chance that one of the runners will die.

Statistical arguments aren't much help if it's your life on the line, so it's natural to look for ways of screening out the risk. Indeed, autopsies after such deaths reveal heart abnormalities in all but about 6 per cent of cases, Dr. Thompson says.

But it doesn't necessarily follow that we can screen for these abnormalities. About 10 per cent of healthy athletes display abnormal electrocardiograms - and upon further examination "you keep finding more little abnormalities," producing an impractically high rate of false positives, Dr. Thompson says.

Dr. Redelmeier agrees. His analysis indicates that any screening program would need to be exceptionally accurate and inexpensive to be worthwhile. Otherwise, the resources would be better spent elsewhere - such as to increase paramedic staffing at marathons to respond to the cardiac events that will sometimes occur.

For Mr. Kassap, the cause turns out to have been myocarditis - an inflammation of the heart caused by a virus, which no screening could

have predicted.

"People want a riskless society," Dr. Thompson notes. "So I tell them to go to bed alone."

Alex Hutchinson

is a former member

of Canada's long-distance running team, and has

a PhD in physics.

*****

Beware the final sprint

University of Toronto doctors analyzed 26 sudden cardiac deaths that occurred among 3,292,268 marathoners in the United States. They found that nearly half of the deaths happened in the final mile or shortly after the finish, suggesting that hard anaerobic exercise is about five times riskier than aerobic exercise.

Each heart represents a sudden cardiac death.

Mile 2, one heart

Mile 9, one heart

Mile 10, two hearts

Mile 14, one heart

Mile 15, one heart

Mile 17, one heart

Mile 20, one heart

Mile 21, one heart

Mile 22, three hearts

Mile 23, one heart

Mile 24, two hearts

Mile 26, eleven hearts

TRISH McALASTER / THE GLOBE AND MAIL

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