Review: The Haywire Heart

 One of my colleagues died in 2024, supposedly during a bike ride. The guy was fit, frequently passing me as though I was standing still, and the family (understandably) didn't disclose many details about what happened other than it was a sudden cardiac event.

I ran across an Outside article about Leonard Zinn getting into trouble because of years of endurance training. This was more fully documented by a book, The Haywire Heart. The book fully acknowledges that there can be no final medical study on whether excessive endurance training will cause you to die or get really poor medical outcomes. That's because you can't do a randomized blinded trial! On the other hand, intuitively we all understand that overdosing on any kind of medicine (and exercise is frequently listed as a medicine) can (and does) kill you.

The book starts with a description of what the heart does, and how both the muscular and electrical systems work. It's amazing how much the heart does, even in  sedentary person:

the heart produces as much energy in a single day as a 100-kg boulder does while falling from a building 383 feet tall (or as much energy as it would take to lift that boulder up to that height). That would leave a big dent in the sidewalk; 15 states in America don’t even have a building tall enough to do this experiment! The mechanical efficiency of the heart is less than 10 percent,9 so the heart will demand over 10 times as much energy (in Calories) as it produces, or in this case, 10 × 115,000 J = 1,150,000 joules in a day, or 1.15 × 106 J × 0.239 cal/J × 10-3 Cal/cal = 275 Calories. In other words, your resting heart requires about one Clif Bar per day in order to keep ticking. (page 43)

 The book has scattered throughout articles about various athletes who've succumbed to over-exercise syndrome. Some of these (including Dave Scott, multiple ironman winner) you might have heard of. The book describes how hard it is for athletes to get appropriate attention and medical care from doctors:

Most doctors don’t know the sensation of being in a road race, criterium, or time trial. They’ve never been in the gutter because of a crosswind, saying to themselves, Ten more pedal strokes, just do it for 10 more pedal strokes. Hold that wheel! Don’t let go! Most doctors don’t know the effort it takes to bridge across to a breakaway. When normal people feel the sensation that a curtain is closing in on their peripheral vision, they turn the tension down on the exercise bike or reduce the speed of the treadmill. They pull the plug on the pain. They are normal. Competitive athletes are not....at a European heart meeting where a doctor presented a case including an ECG that showed a heart rate of 32 beats per minute. The presenter withheld the fact that the ECG belonged to an athlete. He then asked the audience which treatment they would recommend. The audience response system, an automated way to ask the audience questions and compile the most common answers, revealed that a significant number of attendees recommended a pacemaker. Before the first presenter could clarify things, a fiery senior presenter stepped to the microphone and chastised the audience. He was visibly angry. He used the example of five-time Tour de France champion Miguel Indurain, who famously boasted a resting heart rate of 28 bpm. (page 144, 146)

 The book acknowledges the complete lack of data and studies. For instance:

research paper from Denmark garnered significant attention in the lay press because it boldly concluded there was a U-shaped association of running and death rate.62 That is, light and moderate joggers had lower death rates than sedentary controls, but strenuous joggers had death rates similar to the sedentary controls. This paper, with its common-sense conclusions, suffered from a severe statistical problem: The group of vigorous runners included only 36 of more than 1,000 runners in the study. Although the authors reported that vigorous runners had nearly twofold higher death rates, the confidential intervals were wide, ranging from a 50 percent lower death rate all the way up to an eightfold higher death rate. You simply cannot draw any conclusions from this sort of data. (page 111)

What's interesting is that the book doesn't recommend running out and getting tested immediately! That's because there's a huge risk of over-treatment! The book has a horror story in which someone got an MRI and that turned into a series of tests culminating in a completely unnecessary procedure that did permanent damage to that person's heart!

OK. What are you supposed to do? Well, you're supposed to listen to your body. By the way, that's a dangerous advice when you're reading this book, because after reading all these horror stories I found myself more sensitive than usual and can easily believe that I would hallucinate issues even when there were none. I'm very grateful now that my Garmin connect frequently tells me that I'm too lazy to have sufficient "high aerobic" or "anaerobic" workouts! (On the other hand, my 23andMe results once told me I hada high chance of Atrial Fibrillation)

In any case, the book recommends a few supplements that haven't been shown to do any harm (CoQ10, magnesium). They also recommend backing off a bit on the ultra-high-intensity events and intervals that people who are training for hard races do. I think that probably makes sense --- I observed that last year's tour was particularly easy, and I ended the tour stronger than at the start because I was resting so much. That's probably a much healthier tour than a full on, push yourself to the limit every day day after day!

The book's worth reading, and then giving yourself some time off to avoid being a hypochondriac before taking its advice to heart. Fortunately, most people are unlikely to ever push themselves to hard for whom exercise overdose is even a potential problem.