Most of us should recall from physiology class that familial
hypertrophic cardiomyopathy is a common genetic heart disease that results in
hypertrophy of the cardiac muscle (1). The hypertrophy of the myocardium
results in a less efficient heart and the left ventricle cannot pump blood to
the body effectively. We should also know that when we exercise we strengthen
the heart and there can be exercise-induced hypertrophy of the heart muscle.
The question is, does exercise-induced hypertrophy cause heart damage?
The Journal of Physiology published multiple views on this
topic last month. The answer: yes and no. Guasch and Nattel argue that
endurance training can lead to myocardial damage (2). They point out multiple
studies that show an increase in incidence of arrhythmia atrial fibrillation
due to an enlarged right ventricle and myocardial fibrosis as a result of
high-intensity training (2). Specifically, high-intensity training increases
cardiac output, and blood pressure, increasing aldosterone and cycles of
inflammatory cytokines.
However, Ruiz et al. report that the elite endurance
athletes live longer and in general are more heart-healthy. They state that
there is only an association between the
increase risk in developing atrial fibrillation and high-intensity training and
furthermore report that the group that is at high risk is limited to
under-trained middle-aged runners after long endurance events (3). Also, the heart rate variability of
trained athletes is also heart-protective and the long-term implications of
atrial fibrillation are limited.
It appears that there are questions that still need answers:
Does too much high-intensity training exist? If so, how much is too much? Will
the benefits always out-weigh the (potential) risks?
You can follow this debate between Guasch & Nattel and
Ruiz et al. with The Journal of Physiology.
References:
1. Familial hypertrophic cardiomyopathy. U.S. National
Library of Medicine.
http://ghr.nlm.nih.gov/condition/familial-hypertrophic-cardiomyopathy
2. Guasch E, Nattel S. 2013 Oct. CrossTalk proposal:
Prolonged intense exercise training does lead to myocardial damage. The Journal
of Physiology. 591:4339-4941 Retrieved from: http://jp.physoc.org/content/591/20/4939.full
3. Ruiz JR, Joyner M, Lucia A. 2013 Oct. CrossTalk opposing
view: Prolonged intense exercise does not lead to cardiac damage. The Journal
of Physiology. 591:4343-4945 Retrieved from: http://jp.physoc.org/content/591/20/4943.full
4. Guasch E, Nattel S. 2013 Oct. Rebuttal from Eduard Guasch
and Stanley Nattel. The Journal of Physiology. 591:4947.
http://jp.physoc.org/content/591/20/4947.full
5. Ruiz JR, Joyner M, Lucia A. 2013 Oct. Rebuttal from
Jonatan R. Ruiz, Michael Joyner and Alejandro Lucia. The Journal of Physiology.
591:4949. http://jp.physoc.org/content/591/20/4949.full
This was a very interesting issue you brought up and after reading up on Guasch & Nattel and Ruiz et al., they both have very good arguments. When writing this who do you believe had the better argument, just out of curiosity? Also, I am curious to know if any of your research provides reasons on other factors that may make elite athlete more heart healthy. I could see there maybe being an issue of resting heart rate to take into consideration, since it would vary between those that engage in high aerobic training regularly and those who do not. Perhaps both may develop hypertrophy but since at rest an athletes HR would be much lower than the average person, the stress on the heart could be lesser?
ReplyDeleteMia,
ReplyDeleteI think that would be interesting to see if they come to a conclusion after further research. I feel like it would be an in-between of those two views, subject more to individual variance since each person is so unique. I think this also comes back to the fact that it is a multi-faceted topic, particularly when thinking about high-intensity training. This kind of training will build additional muscle, which will require more oxygen, and thus increase blood volume and cardiac output. This could also additionally increase cardiac muscle size. I guess the question is at what point is there an increase in the risk? Did you come across any research that showed a general scale of risk for side-effects of high-intensity training?
Mia,
ReplyDeleteThese topics in physiology and your blog discussion are always friendly reminders that I need to work out more often☺. Anyways, I did a little research in order to attempt to answer your questions. I found a couple of articles that offered a bit of insight, but as you pointed out, there is still a debate about this topic.
One article from Discovery News mentioned that there are some small studies that imply that elite and serious athletes were more prone to developing irregular heart rhythms, especially those under 45 years of age. For this study, the researchers followed decades of individuals who skied the Vasaloppet, an annual 56-mile cross country ski race held in Sweden. In fact, their results indicated that those who had competed in the skiing event seven or more times were almost 30% more likely to seek medical attention for heart arrhythmias compared to those who had only participated once. Also, taking into account income, age and other contributing factors, the study concluded that participants who completed the race around the same time as the winner were hospitalized for arrhythmias 37% more often than competitors who finished in twice the time as the winner (Discovery News 2011).
In another article published in the Boston Globe, Dr. Paul Thompson, a 29-time Boston marathon runner and cardiologist, was also intrigued by the damaging effects of high-intensity training on the heart. In recently published papers he, too, insinuates that high-endurance activities, like running marathons regularly, can increase the risk for heart arrhythmias, cause harm to cardiac tissue, and lead to the development of hardened arteries (Kotz 2013).
There seems to be a consensus that exercising at a more moderate pace and for a more moderate amount of time is more beneficial and may even extend one’s life, compared to pushing oneself harder and longer.
However, there are still those who believe the evidence is not strong enough to warrant scaling back on intense workouts. In fact, Dr. Benjamin Levine, a cardiovascular physiologist, still believes that despite some evidence of high-intensity workouts causing harm, “plenty of research shows that even extreme exercise offers far more benefits than risks to the heart” because it’s “a prescription for life “ (Discovery News 2011).
References:
2011. Too much exercise might harm your heart. Discovery News. [Internet] Available from:
http://news.discovery.com/adventure/endurance-athletes-arrhythmia-110908.htm
Kotz D. 2013. How much exercise it too much? Growing evidence shows that overdoing endurance training may damage your heart and shorten life expectancy. But don’t hang up your running shoes and wetsuits just yet. The Boston Globe. [Internet] Available from: http://www.bostonglobe.com/lifestyle/health-wellness/2013/08/04/can-too-much-exercise-harm-heart-and-shorten-your-life/VLlkXGBN9f1t6raYmUSuPJ/story.html
Great comments Danielle! I would like to read the Kotz 2013 in more detail- My question would be: do the arrhythmias really cause harm? I remember reading somewhere (I need to look it up) that heart rate variability was correlated with a decrease in cardiovascular disease, but do the arrhythmias seen here go beyond that? Also, the increase harm to cardiac tissue and the hardened arteries seen in that study outweigh the benefits of exercise? Are they more at risk than the average person or non-athlete? I hear various arguments about inflammation: high-intensity exercise reduces inflammatory molecules in some studies and in others it seems to increase inflammatory molecules... I still have a lot of questions!
ReplyDelete