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Endurance exercise 'may damage the heart'

“Marathons can damage you heart,” according to a report in the Daily Mirror.

BBC News and The Daily Telegraph reported similar findings based on a small study that examined the hearts of 40 endurance athletes before, immediately after and one week after endurance events. These events ranged from a regular marathon (42.2km of running) up to an ultra-triathlon (comprising a 3.8km swim, a 180km cycle and then a full marathon).

The research found that immediately after the race there was a small, generally temporary drop in the efficiency of the right ventricle, the chamber of the heart that pumps blood to the lungs. However, as both the researchers and newspapers have pointed out, this doesn’t mean that endurance exercise is bad for you. This dysfunction fully recovered after one week for most athletes, although five had signs that the dysfunction may have lasted longer than a week. These athletes tended to have been competing in endurance events for longer (about 20 years).

The athletes studied were highly trained (they did more than 10 hours’ training a week) and so their results wouldn’t reflect those of people who do less exercise or more moderate activities. Also, the small number who did not recover within a week may have eventually gone on to do so. The many health benefits associated with regular exercise are well publicised, including the benefits exercise has for heart health.

 

Where did the story come from?

The study was carried out by researchers from a range of academic and clinical departments based in Belgium and Australia. It was funded through a scholarship from Australia’s National Health and Medical Research Council and a Cardiovascular Lipid Grant from the Pfizer pharmaceutical company.  It was published in the peer-reviewed publication European Heart Journal.

The news coverage of this article was generally well balanced and informative, with BBC News, The Daily Telegraph and the Daily Mirror all explaining that the impairment was temporary in all but a few endurance athletes. Many also included quotations from the study’s author emphasising that the study should not be interpreted to mean endurance exercise is bad for you.

For example, the Telegraph quoted the main study author, who said: "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."

 

What kind of research was this?

This research was a small cohort study of endurance athletes looking at their heart structure and function before, immediately after and one week after they took part in an endurance race.

Research on athletes’ hearts has generally centred on the left ventricle, which is the chamber of the heart that pumps blood to the body once it has been oxygenated from the lungs. This study aimed to compare the effects of endurance exercise on the right and left ventricles. The right ventricle is the chamber of the heart that pumps blood towards the lungs to be oxygenated.

 

What did the research involve?

Through local triathlon clubs the researchers recruited 40 healthy endurance athletes due to compete in one of four types of endurance event: a marathon, an endurance triathlon, an alpine cycling race and an ultra-triathlon. The four events were chosen to represent different durations of intense exercise.

To be included in the study, athletes also needed to:

  • train intensively for more than 10 hours a week
  • have finished in the top 25% of competitors in a recent endurance event
  • have no heart complaints or pre-existing risk factors for heart conditions
  • have no heart abnormalities detected during an initial assessment of heart function and structure

A range of techniques, including 2-D and 3-D ultrasound scans (echocardiograms), were used to look at the structure and function of the athletes’ hearts before, immediately after and one week after they took part in an endurance race. The researchers also took blood samples (to measure chemical markers of heart stress) and used MRI scans to look for possible signs of scarring or damage to the heart.

The distances, number of competitors and completion times for each event were recorded to give an idea of exercise intensity and performance. The average duration of the different events varied greatly, with the marathon (a 42.2km run) taking an average of three hours and the ultra-triathlon (a 3.8km swim, a 180km cycle and then a 42.2km marathon) taking an average of 11 hours.

Researchers then compared structural and functional information on the athletes’ hearts from each of the time points between individuals and between individuals competing in the different endurance events.

 

What were the basic results?

The study found that, after endurance exercise, the volume of the right ventricle chamber (pumping blood toward the lungs for oxygenation) was larger than before the race and that this impaired its ability to eject blood from the heart chamber. The research found that the amount of impairment to the right ventricle was linked to the race duration, with longer races causing greater impairment.

By contrast, the left ventricle chamber decreased in volume slightly after exercise, but its function was not affected.

The researchers found it significant that, for the majority of athletes, all measures of heart muscle function returned to normal within a week of the endurance race. However, five of the athletes (13%) showed signs of more long-term effects when assessed at one week (a persistently lower ability of the right ventricle to eject blood). These athletes had been competing in endurance events for longer than those who did not show signs of lasting damage (approximately 20 years of competing versus eight years of competing).

 

How did the researchers interpret the results?

The researchers concluded that intense endurance exercise caused temporary dysfunction in the right ventricle but not the left ventricle. They also concluded that, while most athletes completely recover from these temporary changes, more long-term changes and reduced function in the right ventricle are evident in some of the athletes who had been competing in endurance events for a long time.

 

Conclusion

This study assessed the heart function of 40 healthy endurance athletes and showed that a small dysfunction in the right ventricle was present immediately after an endurance race. In approximately 9 out of 10 of these athletes this dysfunction was temporary, disappearing after one week. In a minority of cases the results showed some dysfunction in the right ventricle may last longer than a week. The study suggested the longer-term effects may be particularly likely in people who have been competing in endurance events for many years.

When interpreting the results, the following limitations should be taken into account:

  • The research was done using only 40 individuals and so these may not be typical of all endurance athletes. Studies with larger numbers of athletes would be needed to confirm these findings.
  • The athletes studied were highly trained (doing more than 10 hours of intense training a week) and so these results do not relate to those undergoing less or more moderate levels of exercise.
  • Although some online news sources have suggested that running a marathon could damage the heart, it was the more strenuous events that were most strongly associated with heart dysfunction. These extreme endurance events included an ultra triathlon (11 hours of continuous, strenuous exercise involving a 3.8km swim, a 180km cycle and then a full marathon).
  • The athletes’ final heart scans were one week after competing in their event. It is possible that any heart dysfunction observed at this point would eventually recover, and so longer-term checks would be warranted.
  • The finding that the most trained athletes may be more at risk of longer-term dysfunction is not proven by this study. Larger studies involving more athletes followed up over a longer period of time are needed to confirm this finding, and to see whether any effects last longer than one week.
  • The clinical effect of this dysfunction also needs further investigation as it is not clear whether this will lead to an increased risk of cardiovascular disease or death.

The many health benefits associated with regular exercise are already well known. As emphasised by the study authors and the news coverage, this study does not suggest that endurance exercise is unhealthy. It simply notes that, in a small number of endurance athletes, there may be a risk of dysfunction that lasts longer than one week.

 

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