Vigorous Exercise—Too Much of a Good Thing, Continued: Studies on Atrial Fibrillation

More than a year ago I wrote an earlier blog titled “Exercise, part 2: Moderation in all things?”  I reviewed studies that indicated that intense aerobic exercise may lead to damaged heart and arterial tissues.  Pretty scary for those of us that do long duration exercise.

This topic continues to evolve, and I thought I’d bring this topic up to date, and focus at this time on one aspect of heart damage: atrial fibrillation.  

Many, many studies support the thesis that exercise is beneficial to people of all ages.  Beneficial to one’s physical as well as mental health.  And I, too, believe that.

And many believe, logically, that if a little exercise is good for you then more is better.  And much more would logically be much better.  

Indeed we have become a culture of long distance runners and cyclists.  Well, not quite a “culture,” but the statistics on the number of people running marathons (full marathon is 26 miles) have gone up dramatically since the 1970’s.  In 1976 there were an estimated 25,000 who ran a marathon; in 2012 there were 500,000, an increase of 20 times.

I suppose everyone has heard of The Complete Book of Running, published in 1977.  It was a best selling book, authored by Jim Fixx (actual name James Fuller).  And probably Jim Fixx can be credited with starting the running craze that is still with us.

And so it was ironic when Jim Fix died in 1984, after his daily run, at the age of 52.  I think the world did a pause and said…ummmm.  But it soon came out that Fix had a genetic predisposition to heart problems, and we all went happily back to running.

Fast forward to 2009.  At that time another book was published, Born to Run, by Christopher McDougall.   I thought it was over all a fine book, especially when it stuck to “the science.” In it he prominently featured an ultramarathon runner, Micah True (aka Caballo Blanco).

But, Caballo Blanco died in 2012, aged 59, during a run.  

An autopsy showed that True was suffering from cardiomyopathy (general word covering a deterioration of the heart) for no known cause.  

It turns out that scientists have been studying the effects of “extreme” exercise on heart health for several years now.  And I think I’m safe in saying that the science is not yet “settled”, but there are some patterns emerging….I think.

Now some heart-vocabulary.  First there is “atrial fibrillation” (called here AF).  It results when the two small chambers on top of the heart (the atria) don’t beat in unison.  It affects 0.4 to 1% of the general population, and its incidence increases with age, going up to 8% for those over the age of 80.  Next we have the ventricles—the two large chambers forming the bottom of the heart. There are right and left ventricles—the right being the largest, but the walls of the left are thicker.

It seems the first studies on exercise and the heart concerned AF.  Back in the mid to late 1990’s some studies suggested that extreme exercise may be associated with AF.  For example a 1998 study of competitive Finnish Orienteers, average age of 47.5 years, had AF at 5.5% over controls.

Since that time there have been two large studies—The Physicians’ Health Study and the Cardiovascular Health Study.

The Physicians’ Health Study was reported in 2009.  It was based on the exercise habits of 16,921 men (Physicians) who ranged from doing no exercise to those who exercised 5-7 days per week.  After 12 years of follow up they found that the incidence of AF was about 1%, and that there WAS a relation between AF and amount of exercise: men who jogged 5 or more days per week had a 53% increase in AF.  Further, this trend was only found in men younger than 50 years old.  Interestingly, for men over the age of 50 there has no correlation between AF and exercise.

Let’s stop there and keep these numbers in perspective.   So this 2009 study found that in the worst case scenario the incidence of AF went up to 1.53% of the population studied.  That is, 1.53 men out of 100 men developed AF. And, this occurred only in younger men.

In 2008 the results of the Cardiovascular Health Study were published.  Here they looked at “walkers” only, and placed them into categories of how far and fast they walked.  They found that the faster and longer they walked, the lower the incidence of AF.

The 2008 and 2009 studies are not really comparable—the 2009 study included runners, while the 2008 only had walkers.  But, both of them together may imply that “light/moderate” exercise reduces AF while more intense exercise increases AF (though still at a low percentage).

A 2013 study that looked at ~45,000 walkers and runners and ranked them in energy expenditure.  Their average age was greater than 50 years, and they all had run or walked for greater than 9 years.  After studying this population for an average of 6.2 years they found 1.) the incidence of AF was 2.3%, and 2.) the greater the exercise intensity then the LESS incidence of AF.

A very recent study looked at 44,410 Swedish men who were AF free at the start of the study in 1997.  They ranged in age from 45-79, and were asked to rank themselves on levels of exercise throughout their lifetimes. There were a couple interesting results: 1.) after 12 years of follow-up there were 4,568 cases of AF, or 10.2%; 2.) for those men who had the greatest levels of exercise by the time they were 30 years old, they had 19% more AF by the time they were averaged 60 years old.  And, if they had no intense exercise AFTER the age of 30 they had a rate of 49% greater than controls.  

Wow.  These results suggest that greater physical activity when young resulted in greater AF when old. Even if they stopped exercising.  What?

And so, generally, that’s where we seem to be.  It does look like a muddle. Some studies say yes, and some say no—but the preponderance of the evidence is, yes—that the highest levels of exercise will increase the frequency of AF.  Is exercise uncovering or “forcing” a predisposition to AF?  Many are now recommending that we engage in more moderate amounts of exercise.  The problem is, no one knows how much is “moderate,” and overall, I think many agree, the benefits of moderate to extreme exercise outweigh the “low” frequency of AF.

There are other studies that have reported on plaque, left and right ventricle changes, and other modifications to the heart as a result of exercise.  

A 2014 editorial in the American College of Sports Medicine essentially concludes that “extreme or obsessive exercisers…are at more risk than for those that practice moderation.”

Of course managing risk is something we do through out our lives, in all sectors.  Balancing risk and reward is always a problem. Understanding the level of risk is often a challenge, and often editorials, such as the above 2014 editorial, don’t seem willing to attach a number to “risk.”  I can’t fathom how anyone can manage risk without knowing the basic statistics behind “risk” statements.

Anyway, I will  continue  on exercise and heart issues in my next blog.

Useful References

1.) 2008; 118(8): 800-807

2.) 2014 Annual Marathon Report
Date: March 23, 2014
3.) 2009 Am J Cardiol. Jun 1;103(11):1572-7. doi: 10.1016/j.amjcard.2009.01.374. Epub 2009 Apr 22.
Relation of vigorous exercise to risk of atrial fibrillation.

4.) 2013. doi:  10.1371/journal.pone.0065302
Reduced Incidence of Cardiac Arrhythmias in Walkers and Runners
Paul T. Williams1,* and Barry A. Franklin2

5.) Heart 2014;100:1037-1042 doi:10.1136/heartjnl-2013-305304
Atrial fibrillation is associated with different levels of physical activity
Drca, N. et al.

6.) 2014. ACSM'S Health & Fitness Journal:
July/August 2014 - Volume 18 - Issue 4 - p 47-49
doi: 10.1249/FIT.0000000000000047
Have a Heart: Can Too Much Exercise Be Bad?
Asplund, Chad A. M.D., M.P.H., FACSM