CW: That exercise has an upper limit makes perfect sense

As a bike-racing heart doctor who practices in one of America’s least healthy states, it pains me to say anything against exercise. I spend a great deal of my typical office day cajoling Kentuckians to exercise more. Sometimes, I even prescribe daily exercise rather than a medicine!

“It’s OK to exercise every day that you eat,” I often say.

The simple triad of wellness is good movement, good food, and good sleep.

But…could exercise be like aspirin: one per day is good, but eight, not so much? Is it possible to exercise so much that our hearts break down?

The scientific data that looks at those who insist on running multiple marathons, cycling many centuries and swimming across channels (the so-called ultra-endurance athlete) looks consistently unsettling.

Today, in the NY Times, Gretchen Reynolds, beautifully ties together two human studies and one rat study that shed a light on the detrimental cardiac effects of ultra-exercise. Here’s a blog-length summary of the three studies she mentioned:

  1. In a very small study from Doha, Qatar, 12 lifelong veteran male endurance athletes underwent MRI scans of their hearts. Six of the twelve men showed evidence of heart scarring (fibrosis). Younger athletes, and regular people, in comparison, had no scar tissue.
  2. In a German study of 108 middle-aged marathon runners, the prevalence of heart (coronary) artery calcium deposits–a marker of blood-vessel disease–was markedly increased. This finding surprised investigators because “on paper” the marathoners were ‘healthier’ (Ed. note: there are now confirmatory trials showing that marathon runners are at increased risk for calcium deposits in the heart arteries.)
  3. Finally, Ms Reynolds tells us about yet another rat study— not just regular rats, but “Marathon Rats.” These were rats that could tolerate running for extended periods on a rat treadmill. (A grid on the back of the treadmill delivered a “small,” non-painful shock to “encourage” rats to run effectively.) The Canadian and Spanish researchers learned three things when they compared the over-trained rats to slacker rats: (1) The marathon rats developed scar in their hearts; (2) The over-trained rats were more susceptible to heart rhythm abnormalities; and (3) Scar tissue and arrhythmia susceptibility resolved after they stopped running.

Taken together, these three trials add to the increasingly large pool of evidence that links chronic physical (over)stress to heart disease. Things like:

  • The consistent reports of athletic middle-aged people who die suddenly at events like marathons and triathlons.
  • The strong association of endurance athletics and atrial fibrillation.
  • The fact that the number one cause of non-heart-attack-related (non-ischemic) heart muscle weakness is persistent revving of the heart rate—we medical people call this tachycardia-mediated cardiomyopathy.
  • Heart enzymes—the same ones released in a heart attack—rise after running marathons.

That all this science points to chronic exercise as maladaptive makes perfect sense to those of us who fancy the views of the famous 19th century British naturalist, Charles Darwin. For back in the day when human survival required hunting our own food, and avoiding becoming food for another species, the ability to twitch very rapidly, repeatedly, was far more desirable than the ability to drudge around for hours at ‘endurance’ pace. In other words, being able to run one fast mile was better than being able to run 26 slow ones. Those that were alert, fit and rested were more likely to keep their DNA going forward.

Go fast, rest, and be well.

Or, be an ultra-person. Just don’t count on being ultra-healthy.

JMM

P.S. How do you know how much exercise is too much?

That’s a tough one to answer quantitatively because all humans have different tolerances to inflammation. Remember not all the rats and endurance athletes showed heart scar. But as a general rule, if on Monday, the old guy pushing the IV pole down the hall is walking faster than you, it’s a good bet that you went a little too long on Saturday and Sunday.

5 comments

  1. John- I guess the question you leave us with is, where is the cutoff point? I have a friend who was told half-iron man okay full iron man no way. How do we know where the fun hurts too much? Scary as so many of our friends push these limits competitively, in events and w each other.
    Perplexing as to where we draw the line, but not a shocking finding.
    bs

    1. BS,

      Since your blog is entitled, “Love the Pain,” and your last post had the words, “Death March,” your question is interesting.

      I do not know where the threshold is for trouble. Also, I don’t want my statement
      of facts to be considered as an overly progressive view that says we should vilify endurance athletics. There has been little doubt in my mind that what we do as an avocation is good for us over the long run.

      But, as a doctor interested in the role of inflammation in wellness, the ultra crowd serve as compelling subjects of study.

  2. “…The over-trained rats were more susceptible to heart rhythm abnormalities…” and they also likely experienced fatigue, depression, anxiety, sleep disturbances, difficulty concentrating, irritability, emotional lability and loss of libido. At least, those are the common symptoms described in the 3rd edition of the book Sports Medicine Secrets in those (rats or humans) with ‘overtraining syndrome’.

    For example:
    “Multi-sport athletes and ultra-marathoners may exhibit obsessive-compulsive disorder in their attempts to log increased mileage in training”.

    Plus they have no lives ….

  3. John,

    While the measure of a lab value or radiographic finding is interesting, I’d be more interested to know what, if any, correlation exists between exercise duration/intensity/frequency and paramaters that I’m used to dealing with: overall surviveal, (cardiac) event free survival, disease free survival, etc. A lab or radiographic finding without a meaningful clinical correlate is of suspect value.

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