We all know that physical activity is essential for our health, and it therefore seems logical that participating in extreme endurance sports such as marathon running is good for you. Several studies have indeed shown that endurance athletes live longer and healthier than the general population.
As a keen runner, I have always believed this, even though running means much more to me than just a healthy habit.
However, there is now a mounting amount of evidence suggesting that lifelong endurance athletes suffer more from heart rhythm disturbances than the general population. In the largest study we have today, Dr Aizer and colleagues demonstrated that men who exercised hard 5-7 times a week had a 20% increased risk of rhythm disturbances than sedentary healthy people. They also showed that runners were at the highest risk. Could it be that some athletes are doing too much?
We are talking here about a small group of extreme endurance athletes. Most people do not exercise enough to be at risk. The affected athletes are typically in their forties or fifties, and have been involved in competitive endurance sport since their youth. On average they have trained for 36 years. On the other hand, very vigorous exercise could protect you against premature death, as recent studies have shown that Tour de France’s cyclists and cross country skiers live longer and healthier than the general population. This makes the occurrence of rhythm disturbances even more puzzling.
Cardiac magnetic resonance imaging (CMR) is currently the best imaging technique we have to evaluate the heart. It gives us clear images of its anatomy and function in real time, and if we use a contrast product such as gadolinium, we can look at its blood perfusion and diagnose areas of fibrosis. Recently, scientists have used this technique to examine runner’s hearts before and after completing a marathon.
These studies are small (CMR is an expensive examination!) but in general the results indicate that the right heart can become overworked. In some people, this leads to a dilatation of the right ventricle and atrium, which normalises in a week to a month. There was no relation between fitness (as measured by VO2 max), training mileage or marathon experience and right heart dilatation. It is thus likely that some people are more susceptible because of their genetic make-up.
A few years ago, Dr Breuckman and colleagues demonstrated areas of fibrosis in seasoned marathon runners, but they were not sure what the cause was. It was an important finding though, because fibrosis in the right heart muscle makes you prone to heart rhythm disturbances.
In 2011, Dr Benito and colleagues published a study on rats which ran vigorously for up to 16 weeks. This corresponds to about ten years of daily intense training for humans. They noticed areas of fibrosis in the hearts of the rats who ran, and none in the sedentary ones. They concluded that lifelong intense endurance training can lead to fibrosis. Most scientists now believe that this could be explained by repeated dilatation and recovery of the right heart chambers. Interestingly, the fibrosis disappeared when the rats were allowed to stop running for eight weeks.
It is obvious that we need more research. For example, we do not know if and how we can diagnose the problem at an early stage, or if we can decrease the risk by altering the training regimen.
Exercise has many health benefits, but it is not because you are a very fit athlete that you are immune from heart disease or other health conditions. You still have to look after yourself.
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