Is endurance training bad for you?
This was a tough article to write for a couple reasons.
First, the research out there is tricky, and occasionally confusing and contradictory.
But secondly, and more importantly, I very much wanted the data to say that endurance exercise is not at all detrimental to your health. I love training and racing.
And while I’m in a bit of a hiatus with the extreme end of the sport due to family considerations, I’ve had a lot of fun with ultra-endurance triathlons and 24-hour mountain bike races and might want to return to some competition in a little bit.
Unfortunately, from what I’ve read up to this point, I’m not terribly optimistic about what the research shows in regards to the long term health and viability of training and racing ultra-endurance events. Much of the research on this subject makes it clear that there are sometimes severe consequences for the years of intense endurance training and racing. There are some contradictory studies though so as with most research we can say that it isn’t definitively bad for you. But I regret to inform that there is ample evidence to suggest that intense exercise over many years can affect your cardiac health.
What do these studies look at?
Studies look at a number of different areas. The few that I’ll focus on are chemical markers, heart function changes, and imaging of the heart to define it’s layout and tissue structure.
Biomarkers are chemicals that are released by the heart in certain stressful situations — like cardiac troponin.
Heart function changes that studies looked at are the ejection fraction of the heart (the percentage of blood the heart is pushing out of its ventricles in a single heart beat), stroke volume (the total volume of blood expelled in a heart beat), measuring pressure at different parts of the heart, or even at electrical changes, like conduction velocity.
The main form of imaging I began to focus on was Cardiac Magnetic Resonance (CMR – like an MRI of the heart) with Late Gadolinium Enhancement (LGE) which can identify any dead tissue in the heart. This seems to be the closest thing to a gold-standard for determining long term damage to the heart since heart tissue is mostly unable to replicate and repair itself once it dies. When we have a heart attack, a part of the heart muscle goes without blood for a period and becomes necrotic (dies) and those muscle cells won’t work again so heart function is impaired.
Where does the research start?
Numerous studies (like this one, this one, and this one) document short term cardiac changes — in biomarkers and heart function tests — following a marathon or an ultra-endurance triathlon. Nearly all show changes in heart function and the stress chemical released. But just about all of them state that these changes are temporary. Temporary is good — so all clear, right?
Not so fast. One study (by La Gerche in the European Heart Journal in 2012) looked at changes to the right ventricle of ultra-endurance athletes following efforts of 3-11 hours in length and found that cardiac biomarkers (like cardiac troponin, and B-type natriuretic peptide) increased immediately following the efforts and that right ventricle ejection fraction decreased — basically some chemicals that denote some strain on the heart increased and the amount of blood the heart pumps to the lungs decreased. The cardiac biomarkers return to normal levels on there own in a few days to a week. But, interestingly the longer the race, the more the right ventricle ejection fraction decreased. Most importantly, one week following the efforts, the researchers looked at the hearts of each athlete with cardiac magnetic resonance (CMR) with LGE (delayed or late gadolinium enhancement) and found evidence of dead heart tissue and scarring.
Another study (by Wilson et al in 2011 in The Journal of Applied Physiology)looked at veteran endurance athletes (mostly marathoners) using CMR with LGE and found higher rates of myocardial scarring than in their sedentary counterparts.
A third study (Hanssen 2011 in Clinical Science) looked at cardiac biomarkers and used CMR with LGE also and while they too found temporary changes in the biomarkers, they did not find any cardiac necrosis (dead heart cells) with the CMR imaging. Why did a few studies find damage and another didn’t? Not sure, sometimes that’s just the way research goes; two steps forward and one step back (or vice versa). In this latest study the researchers did the CMR only one hour after the marathon, while in the first study by La Gerche did their CMR one week after the races and perhaps the week-long interval between race and test allowed for better visualization of the imaging of the heart damage.
There are enough articles on this subject to warrant a “literature review” — basically when a scientist looks up as many articles as they can find on a subject and then writes a new paper to try and distill all that information into a cohesive, but still open-minded explanation of what the body of research is telling us up to that point — and Patil 2012 is a good one to look at. It states
“….chronic, excessive sustained endurance exercise may cause adverse structural remodeling of the heart and large arteries.”
and states its aim to
“….make suggestions about healthier fitness patterns for promoting optimal CV health and longevity.”
What might cause the heart damage and what problems arise?
This is a simplified version as best I understand it, but it appears that intense endurance events cause a release of cardiac biomarkers and this coincides with a temporary decrease in function of the heart. Repetitive events of this nature seems to not allow for complete recovery of the heart tissue and leads to some cell death, especially in the right side of the heart and in the septum (where we have the electrical system of the heart). Because of these mechanisms endurance athletes appear to have more calcium in their coronary arteries (and are at an increased risk of heart attack), more scarring of the heart muscle, and the damage to the cells in the septum seem to lead to higher incidence of electrical issues like atrial fibrillation, among others.
What about the professionals?
It would be logical to assume that since there is an emerging body of evidence that sustained training and racing in extreme long distance endurance events like the marathon, ultra-marathon, and iron-distance triathlon that the professional athletes of these sports would be particularly hard hit with health problems. There is research evidence to suggest that these professional athletes enjoy excellent health and above average longevity. But there is also evidence to the contrary — one study (Baldesberger 2007) found permanent changes in cardiac rhythm among endurance trained elite cyclists. Additionally, although this is technically just anecdotal evidence there is a laundry list of elite level endurance athletes who develop moderate to severe cardiac issues. There are other lists you can find online, but this was one that took me two minutes to find and chronicles a bunch of endurance athletes who have retired (or died) as a result of heart conditions — and I know of a few other names off the top of my head that aren’t on there.
It’s important to note that in the La Gerche and Wilson studies noted above that found higher incidence of cardiac damage among endurance athletes, didn’t find it in all the athletes they studied — they just found it in a higher percentage relative to the rest of the population.
So elites and non-elites alike seem to be susceptible. Perhaps there are some genetics that make someone more likely to develop a cardiac issue? There does appear to be a gene (or genes) that predisposes someone to arrhythmogenic right ventricular cardiomyopathy (ARVC) – which can lead to heart arrhythmias and in extreme cases heart failure. The gene mutation that makes someone more susceptible to ARVC affects things called desmosomes which provide strength to the myocardial cells and help with communication between cells, so the heart becomes weaker. Most of these gene mutations are hereditary and the mutation exists in about 30-40% of people with ARVC, while ARVC only hits about 1 in 1000 people.
Why the discussion about ARVC? There are two studies I found that showed that endurance athletes basically can “acquire” the predisposition to ARVC even in the absence of the genes at a higher rate than non-endurance athletes.
Sawant 2014 states that “…even in the absence of desmosomal and gene-elusive ARVD/C (those who apparently don’t have the gene), endurance athletes still disproportionately develop cardiac problems”.
Another study by La Gerche in 2010 said: “…arrhythmogenic right ventricular cardiomyopathy (ARVC) phenotype may be acquired even in the absence of genetic predisposition”. So even someone who is not genetically predisposed has a greater chance of acquiring cardiac issues by taking up endurance sport.
Believe me, it brings me no joy to have researched this. I am a dyed in the wool endurance junky. But this is a lot….too much….to ignore, at least for me.
So now it begs the question — how much is too much?
That we don’t know with 100% certainty. It’s a function of magnitude and the person. Certainly there are individuals that can do iron-distance triathlons 3 or 4 times a year and run marathons in between as appetizers with seemingly no ill effects. Or at least none now. That’s the hard part since many of these problems won’t arise until later.
There’s a lot more to consider and certainly the jury is out on some aspects of this, but overall this will have me thinking and researching more in the near future.
He lives with his wife and two kids and runs multiple businesses in Grand Junction, Colorado.