Over-exercise risks hurting the heart
THE Vasaloppet, a gruelling 90km cross-country ski marathon held each March in north-western Sweden, provides a convenient venue for studying the impact of intense, prolonged aerobic exertion on the human body.
And the newest Vasaloppet-related study, published last month in The European Heart Journal, is worrisome.
For it, researchers from Uppsala University and other institutions examined the health records of almost 53,000 race participants and found that the more races that someone had completed between 1989 and 1999 or the faster they had finished, the more likely they were to require hospitalisation in the next 10 years for an abnormal heart beat, also known as arrhythmia.
For some time, exercise scientists have wondered if there might be an upper limit to the amount of exertion that is healthy, especially for the human heart.
While the evidence is overwhelming that exercise improves heart health in most people and reduces the risk of developing or dying of heart disease, there have been intimations that people can do too much.
A 2011 study of male, lifelong, competitive endurance athletes aged 50 or older, for instance, found that they had more fibrosis - meaning scarring - in their heart muscle than men of the same age who were active but not competitive athletes.
Heart rhythm is, of course, a complicated affair. Arrhythmias include both abnormally rapid heart rates, a condition called atrial fibrillation if it involves contractions in the atria, or upper chambers of the heart; and ventricular fibrillation if there is disorganised fluttering and contractions in the ventricles, or lower chambers of the heart.
Then there is bradycardia, or a heart rate that is abnormally slow.
In the Vasaloppet study, 1.7 per cent of the racers suffered from some type of arrhythmia in the years after their race, a higher percentage than would be expected among such a fit population. But there was little consistency in the outcomes.
Most of the affected racers developed atrial fibrillation, but some had bradycardia. The one constant was that those racers, male and female, who had completed the most races or finished the fastest were more likely than slower or more infrequent participants to develop an arrhythmia pronounced enough to require medical care.
As Dr Kasper Andersen, a professor at Uppsala University and co-author of the Vasaloppet study, pointed out, "although we observed an increased risk of arrhythmias in the more-trained athletes, physical activity and exercise have positive effects on the risk of other diseases".
However, Dr Andersen did not think that "it has suddenly become dangerous to exercise".
He added that an earlier study he worked on found that Vasaloppet participants tended to live longer than other people in Sweden.
So, for now, his advice to anyone planning a Vasaloppet finish or similar endurance training is simple and commonsensical. "Carry on as usual, but remember to listen to your body and seek a doctor if you experience any symptoms from your heart," he said.