For one-tenth of one per cent of North America’s population, this is a very special time of year. Fall marathon season is about to hit full stride.

Every year, more than 400,000 people finish marathons on this continent.

A few will die trying. And those deaths will make headlines, unlike the countless deaths on those same days that will result from bad diets coupled with a sedentary lifestyle. It’s something I’ve written about before, maybe more than once.

A study from the early 1990s suggested one person in 50,000 will suffer an acute heart attack or sudden cardiac death during — or within 24 hours of — running a marathon or taking part in any other type of exercise that lasts three hours or longer.
Other research suggests that there is one death per 800,000 person hours of running or jogging - in males aged 30-64 who have not been diagnosed with heart disease.

Exercise and death have been the focus of more and more researchers lately. Earlier this year, the European Heart Journal published a study that found that amateur marathon runners who ran less than 64 kilometres per week in training showed signs of cardiac dysfunction after the race. For some, the abnormalities stuck around for a month before going away.

People who put in at least 72 kilometres a week showed no signs of trouble. The more you train, the fitter you get, the less likely you are to stress your heart. Of course, all bets are off if you have a pre-existing condition that you weren’t aware of — which tends to be the case in virtually all strenuous exercise deaths.

Prof. Jack Goodman of the University of Toronto is taking that research a step further. He’s looking at heart function during prolonged exercise, focusing on what might trigger cardiac fatigue. He’ll be particularly watching for the effects on older runners. Goodman says preliminary work suggests prolonged exercise may lead to less effective heart function in the left ventricle.

He — and other researchers — are not saying don’t exercise. What they do suggest is that knowing the condition of your conditioning is critical to exercising safely, as is making sure your heart is healthy.