Monday, February 1, 2016

Good News for Athletes' Hearts

by Larry Creswell, M.D.

Here’s some good news for triathletes on the “too much exercise” front. A recent report in the International Journal of Environmental Research and Public Health takes a look at the heart health of recreational triathletes. The study deserves our attention.

As many readers here will know, there has been increasing attention paid to the possibility that “too much exercise” may actually be unhealthy, particularly for the heart. Over the past couple of years, there have been surprising observations that, at least in small groups of long-term endurance athletes, include unexpected fibrosis or scarring in the muscle of the ventricles as well as abnormal calcification and plaque build-up in the coronary arteries. Although the exact mechanism remains uncertain, one hypothesis is that exercise over the long term might be responsible.

The current study was conducted by a group of investigators in Hagen, Germany, led by Dr. Roman Leischik. He and his colleagues have had an interest in understanding the blood pressure response to exercise. They’ve been investigating the possibility that some athletes, more so than others, have large increases in blood pressure during exercise that might (over the long term) produce “abnormal” thickening, or hypertrophy, of the muscular walls of the heart’s ventricles, or pumping chambers. This is an interesting concept and a plausible hypothesis.

Their most recent article is entitled, “Endurance Sport and ‘Cardiac Injury’: A prospective study of recreational Ironman athletes.” This is actually an observational study, a snapshot look at 87 long-course triathletes who volunteered at the time of an annual medical check-up to participate and undergo two tests of cardiac performance: spiroergometry (a stress test with measurement of heart rate, blood pressure, oxygen consumption, and power output at aerobic threshold, anaerobic threshold, and peak, at exhaustion) and an echocardiogram.

To put the study into perspective, these athletes included 54 men and 33 women. For the men, the mean age was 38 years, the average number of years spent in triathlon was 14.9, and the average weekly training volume was 16.7 hours. For the women, the mean age was 34 years, the average number of years spent in triathlon was 13.7, and the average weekly training volume was 15.5 hours.

There were several important observations:

  1. For men, the mean VO2 at aerobic threshold was 44.7 mL/kg/min and the mean VO2max was 58.1 mL/kg/min. For women, the mean VO2 at aerobic threshold was 38.5 mL/kg/min and the mean VO2max was 52.9 mL/kg/min.
  2. By echocardiogram, the heart function, of both the left and right ventricles, was normal for every subject.
  3. Some degree of left ventricular hypertrophy (LVH) was common. Right ventricular hypertrophy was absent in all of the subjects.
  4. Among the men with the greatest degree of LVH, risk factors included increased blood pressure during exercise as well as overall training time per week.

In my view the findings are not surprising. In part, this might explain why the report was published in a scientific journal that is perhaps a bit off the beaten path. If not for a fellow triathlete who brought the article to my attention, it would have escaped my notice. The major scientific journals are loath to publish “negative” studies, where all of the results are “as expected.” And as a result, many “negative” studies simply go unreported and unnoticed.

The group of triathlete subjects in this study is obviously a serious group of athletes. Their weekly training volume as well as their lengthy participation in the sport suggests that these are not just weekend warriors. From the VO2 testing, these may not be world class or even truly elite endurance athletes, but they are probably very typical of avid recreational triathletes who participate in long-course events. They’re like us; the results are therefore relevant to us.

The athletes’ heart function was normal, even after years of participation. This should provide some reassurance. Granted, this study did not look at other potential downsides of long-term participation such as coronary calcification or myocardial scarring. But keep in mind that there were no functional abnormalities in any of the subjects, in either the left or right ventricles. If such abnormalities do occur in long-time triathletes, we might conclude that they occur with a very low frequency -- or at most, something less often than 1 in 87 athletes.

Lastly, the finding of LVH in many of these athletes should not be surprising. This is an expected adaptation of the heart to exercise and is a typical finding in the athlete’s heart syndrome. The study wasn’t intended to sort out any implications of the hypertrophy, but there is no indication of any adverse consequence. The observed link between LVH and increased exercise blood pressure, at least in men, is intriguing and deserves further study.

In summary, the study offers some evidence that the heart health of recreational long-course triathletes does not suffer during years of participation. That’s some good news.

Reference
Leischik R, Spelsberg N. Endurance sport and “cardiac injury”: A prospective study of recreational Ironman athletes. Int J Environ Res Public Health 2014; 11:9082-9100.


Larry Creswell, M.D., is a cardiac surgeon and Associate Professor of Surgery at the University of Mississippi Medical Center in Jackson, Mississippi. In addition to his regular column on Endurance Corner, he maintains The Athlete's Heart blog to offer information about athletes and heart disease in an informal way and to encourage exchange and discussion that will help athletes build a heart-healthier lifestyle. You can contact him at lcreswell@umc.edu.
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