According to a study published online today in the European Heart Journal, investigators have discovered initial evidence that some athletes who participate in extreme endurance exercises, such as endurance triathlons, alpine cycling, ultra triathlons or marathons might damage the right ventricles of their hearts – 1 of the 4 chambers in the heart that helps pump blood around the body.

The study discovered that even though the damage in the majority of the 40 athletes examined in the investigation was reversed within a week of a competitive event, magnetic resonance imaging (MRI) showed more permanent damage – scarring of the heart muscle (fibrosis) in 13% (5 athletes). The 5 athletes who developed fibrosis competed in endurance sports for longer periods than those who did not show fibrosis.

Dr André La Gerche, a postdoctoral research fellow at St Vincent’s Hospital, University of Melbourne, Australia, who at present, is based at the University Hospitals Leuven, Belgium, explained:

“It is most important that our findings are not over-extrapolated to infer that endurance exercise is unhealthy. Our data do not support this premise.”

Although, André explained that the discoveries did indicate that there may be a few athletes who might have been born with a susceptibility damage as a result of long-term endurance exercise.

André, stated:

“Virtually all of the changes in the athletes’ hearts had resolved one week after having taken part in a competitive event. In most athletes, a combination of sensible training and adequate recovery should cause an improvement in heart muscle function; that is, the heart rebuilds in a manner such that it is more capable of sustaining a similar exercise stimulus in the future. This positive training response can be over months rather than weeks.

The question from our research is whether there are some athletes in whom extreme exercise may cause injury from which the heart does not recover completely. If this occurs, affected athletes may be at risk of reduced performance – a cardiac “over-training” syndrome – of it may cause arrhythmias. If this occurs, it is likely to affect only a minority of athletes, particularly those in whom more intense training fails to result in further improvements in their performance.”

Dr La Gerche and his colleagues in Australia and Belgium enrolled 40 elite athletes in Australia to participate in the study. The athletes were planning to compete in 1 of the 4 endurance events. The participants had no known heart problems, were already well trained (training intensely for over 10 hours per week), and performing well (finishing within the first 25% of the field in a recent event).

The athletes were examined using MRI, echocardiography, and had blood samples taken at three intervals; the first 2-3 weeks before the race, the second within one hour of completing the race, and the third 6-11 days after the race.

Results demonstrated that within 1 hour of completing the race the athletes’ hearts had changed shape, volume increased, while the function of the ventricle decreased. Levels of a chemical called B-type natriuretic peptide (BNP) increased. BNP is secreted by the ventricles in response to over-stretched heart muscle cells. Although after one week, right ventricle function recovered in the majority of the athletes, MRI detected signs of fibrosis in 5 athletes who had been training and competing for longer than the other participants. Furthermore, they discovered that post-race changes to the function of the right ventricle increased with the duration of the race.

Results revealed that the left ventricle, which, to date has been examined the most in athletes, showed no alterations. Dr La Gerche, explained:

“Our study identifies the right ventricle as being most susceptible to exercise-induced injury and suggests that the right ventricle should be a focus of attention as we try to determine the clinical significance of these results. Large, prospective, multi-centre trials are required to elucidate whether extreme exercise may promote arrhythmias in some athletes. To draw an analogy, some tennis players develop tennis elbow. This does not mean that tennis is bad for you; rather it identifies an area of susceptibility on which to focus treatment and preventative measures.”

Dr. La Gerche, concluded:

“It is important to note that this is one component of an evolving understanding of how the right ventricle is the “Achilles heel” of heart function during exercise. We previously studied heart function during intense exercise and demonstrated that the load on the right ventricle (stress, work and oxygen demand) increases to a greater extent than in any of the other heart chambers.

Professor Hein Heidbuchel, who I work with, has shown that the source of ventricle arrhythmias in affected athletes is almost always the right ventricle. Finally, it has been shown that intense exercise in rates causes inflammation, fibrosis and arrhythmias in the right but not the left ventricle. Hence, there are consistent messages, all implicating the right ventricle and yet it has been neglected in the vast majority of studies regarding cardiac changes in athletes. Now there is sufficient evidence to invest in the long-term prospective studies that are required.”

In an associated report, Professor Sanjay Sharma, of St George’s University London (UK), medical director of the London Marathon, explains that even though the investigation is small, “the results provide food for thought and the data should be embraced to galvanize more detailed and longitudinal assessment of large groups of endurance athletes. The potential for such projects is enormous considering the colossal increase in participation rates in endurance events such as the marathon. The long-term conclusions of the authors may appear preposterous to some, but could prove to be the retrospective ‘elephant in the room’.

In a comment for this press release, Prof. Sharma, explained:

“My personal feeling is that extreme endurance exercise probably does cause damage to the heart in some athletes. I don’t believe that the human body is designed to exercise at full stretch for as long as 11 hours a day, so damage to the heart is not implausible. It is too early to say that taking part in endurance sports causes long-term damage to the right ventricle, but this study is an indication that it might cause a problem in some endurance athletes with a predisposition and, therefore, it should be studied further.”

Written by Grace Rattue .