Beware of cardiovascular damage from intense endurance training. There is evidence that the continual stress placed on the heart during intense endurance trainingcauses acute dysfunction in the right ventricle of the heart, the part of the heart that receives deoxygenated blood from the body and sends it to the lungs to pick up oxygen to fuel the working muscles. Acute dysfunction of the right ventricle may lead to enlarging or hypertrophy of this part of the heart, placing stress on the body.
A new study in the European Heart Journal suggests that the acute dysfunction of the right ventricle that comes from intense endurance training occurs in a dose-response relationship such that longer duration training leads to greater impairment. This dysfunction is evident with arrhythmic disorders, which appear as a rapidly beating or racing heart rate for a period of time.
The study measured cardiovascular function in 40 experienced athletes before and after an endurance event. Participants in the study had to perform at least 10 hours of intense training per week and have performed in the top 25 percent of the field in a recent endurance event. They did not have any evidence of cardiovascular risk factors. The study included marathoners, triathletes, ultra triathletes, and alpine cyclists, and the athletes’ cardiovascular function was tested a few weeks pre-race, immediately after a race, and two weeks after the race.
Results showed that the athletes demonstrated a significant immediate reduction in right ventricular heart function following the endurance race. The longer the endurance race, the greater the impairment in function. For example, the marathoners completed their race in less than 3 hours, whereas the endurance triathletes competed for an average of 5.5 hours, the alpine cyclists for 8 hours, and the ultra triathletes for almost 11 hours. In general, right ventricular dysfunction was greatest in the ultra triathletes and least in the marathoners, suggesting that the heart has a finite capacity to maintain the increased work demands of exercise.
The acute immediate reduction in right ventricular function in the athletes correlated with increases in biomarkers of myocardial injury, providing additional data that endurance training may not provide health benefits and does, in fact, cause repeated damage. Researchers expressed concern that athletes that repeatedly place their hearts under such stress will develop myocardial fibrosis, or a hardening of the heart tissues.
In this study, left ventricular function was not changed, which is not surprising since there is evidence that the work demand on the heart with increasing exercise intensity is greater for the right side than the left. Researchers suggest this makes the right side more susceptible to fatigue.
Ten days after their races, the athletes right ventricular function did recover almost to the baseline level that was recorded two weeks prior to the race, indicating that the impairment is short term, but the concern is that habitually stressing the heart in this way and causing dysfunction may lead to longer term poor health outcomes. This concern is supported by the fact that right ventricular function and related biomarkers were all slightly lower than baseline at two weeks, although these reductions were not statistically significant. Also, reports of arrhythmic disorders in previous studies of endurance athletes lend support to the concern.
Take away from this study the understanding that long duration, intense endurance exercise is unlikely to be beneficial for health. Shorter duration endurance or “aerobic” exercise has not been shown to cause the same damage, but it does produce oxidative stress, which will lead to chronic inflammation and may impair organ function. Researchers note that regular exercise is essential for health and well being and has been shown to improve life expectance by seven years over a sedentary lifestyle. This is true—a sedentary lifestyle is one of the worst things you can do for health and longevity, meaning that any kind of physical activity, even aerobic, is better than sitting on your couch watching TV. But, I suggest that the ideal exercise for health, well being, and cardiovascular health is a resistance training program that includes intense energy system training for conditioning and weight management. To learn more about the negatives of endurance training, read The (Many) Negatives of Aerobic Training
La Gerche, A., Burns, A., et al. Exercise-Induced Right Ventricular Dysfunction and StructuralRemodeling in Endurance Athletes. European Heart Journal. December 2011. Published Ahead of Print.
Sharma, S., Zaida, A. Exercise-Induced Arrhythmogenic Right Ventricular Cardiomyopathy: Fact or Fallacy. European Heart Journal. December 2011. Published Ahead of Print.