New book: Too much exercise can hurt the body’s most important muscle

“Haywire Heart” provides research, case studies

by Mike Ivey

I still remember when I realized something was seriously wrong.

It was the day after my birthday five years ago and our regular Sunday morning group was rollerskiing on a country road near Cottage Grove.

Within the first 15 minutes I’d already fallen far behind and was short of breath. My buddies had to wait up for me and one of them joked I must have had one too many the night before.

“No. I’ve skied with a hangover before,” I said. “This is way different.”

On their advice, I cut the workout short and headed back to the parking lot. The next day I called my doctor who told me to come right in.

I explained to my MD that I’d been feeling gassed the past few weeks when I tried to do anything aerobic. Even going up stairs left me breathing hard—scary stuff for someone who thought they were in pretty good shape for an aging baby boomer.

So he listened to my heart. “You’re missing some beats,” he said. I was then hooked me up to an electrocardiogram machine which confirmed my heart was badly out of rhythm.

Unfortunately, it’s become a familiar story for many people as they continue to train hard into middle age. Spend much time around serious endurance athletes these days—the kind who do Ironman triathlons or take 100-mile bike rides—and you’re bound to hear stories about heart problems.

There is a growing body of medical evidence suggesting a lifetime of aerobic exercise can indeed cause heart arrhythmia, a serious condition where the four chambers of the heart are not beating in the proper sequence. I can personally name a dozen friends and competitors dealing with arrhythmias of one sort or another.

Given that we’ve been told for years that exercise is good for you, it seems counter intuitive to think it can actually mess with the proper functioning of your heart. If you’re looking to set a PR in a marathon or just keep up with your pals on the next bike ride, you need that heart working as efficiently as possible.

But studies are showing that long hours of training over decades can indeed change the physical makeup of the heart muscle, throwing off the complicated electrical system that keeps it working properly. Some reports even claim endurance athletes are five times more likely to develop an arrhythmia than the general population.

A new book titled “Haywire Heart” does an excellent job of walking the line between alarmism and reality. It’s co-written by Lennard Zinn, a former U.S. national cycling team member and American Birkebeiner skier; John Mandrola, a cardiac doctor and lifelong runner and cyclist; and Chris Case, managing editor of VeloNews, a sister publication to VeloPress, and author of the article “Cycling to Extremes” that brought the heart issue to national attention.

The Haywire Heart by Lennard Zinn, Dr. John Mandrola, and Chris Case

You don’t usually die from a heart arrhythmia but the condition can lead to strokes or even cardiac arrest in the most serious cases. Atrial fibrillation, or “AFib,” is perhaps the best known since there are lots of TV ads currently touting a blood-thinning drug used to offset the increased stroke risk from it.

Still, exercise-induced arrhythmia is a tricky issue for health officials given the nation’s growing obesity epidemic. The multi-billion-dollar fitness industry also doesn’t want to broadcast that a lifetime of working out could cause some serious heart problems.

Both Zinn and Mandrola have experienced heart rhythm problems that have caused them physical and emotional distress. Serious athletes are often the kind of people who like to drive themselves harder than they probably should. They learn to suffer and learn to love the suffering.



To that end, the book takes special aim at those who may not want to hear the news or think they aren’t hurting themselves with obsessive exercise. The authors aren’t worried about retired Tour de France pros but rather than the weekend warriors.

“It’s the middle-aged people who think they’re training to race the Tour who can’t seem to stop themselves from pushing so hard for so long,” they write.

The 309-page book from Boulder, Colorado-based Velo Press in is certainly the most exhaustive look yet at the issue. It includes chapters on heart function and physiology that even the authors admit might be more information than most readers need.

But where “Haywire Heart” really shines are in the case studies of citizen athletes who have seen their lives turned upside down because of heart arrhythmia. For many of us, things like biking, running or cross-country skiing aren’t just ways to stay in shape. They become a focus of our social lives and a defining part of who we are.

The book acknowledges there is no simple answer to avoiding exercise-induced arrhythmia or dealing with it once it develops. Reducing the volume and intensity of exercise is the best antidote, the authors suggest, along with staying hydrated, watching the alcohol and eating a healthy diet. I was also glad to read about new medical evidence saying caffeine is not a trigger for heart rhythm problems as once thought.

In my case, I was lucky to get relief from a cardiac ablation, an increasingly common procedure where the bad electric circuit in the heart is cauterized to deaden the offending nerve cells. Since then, I’ve returned to biking and skiing, albeit at a lower level of intensity. I’m a tourist more than a racer these days.

The bottom line—and the real takeaway from “Haywire Heart”—is that moderation is indeed the best policy. Reducing stress, taking care of those you love and keeping your goals in perspective is advice we all should follow no matter our chosen pursuit.

Put another way, if you’re sweating it you’re likely trying too hard.

Mike Ivey writes the Footloose blog for


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‘Fast After 50’ Offers High-Intensity Training Advice

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Editor’s note: This is an excerpt from the new VeloPress book, “Fast After 50,” by Joe Friel.

Research tells us that the performance decline we typically experience with aging has a lot to do with how active we are while growing older. For example, a paper released in 2000 examined the combined effects of age and activity level over time. The researchers reviewed 242 studies comparing aging and VO2 max involving 13,828 male subjects. Each of the subjects was assigned to one of three groups based on how active they were: sedentary, moderately active exerciser, or endurance-trained runner. Aerobic capacity was highest in the runners and lowest in the sedentary group. No surprises there. The aerobic capacity changes per decade of life were sedentary, 8.7 percent; active, 7.3 percent; runners, 6.8 percent. What this means is if, at age 30, a man had a VO2 max of 60 and then for the next 30 years didn’t exercise and lived a “normal” (sedentary) life, he could expect his aerobic capacity at age 60 to be around 46. If he was moderately active, it would be about 48. And if he trained as an endurance runner, it would be in the neighborhood of 49. Those are not significant numeric changes. But for normal folks who generally see VO2 max declines of 10 percent and greater for a 10-year period, these numbers are really high.

But regardless of the actual size of the change, here’s the main message: The study further reported that the subjects who were endurance-trained runners significantly decreased their volume (miles run per week) and training intensity as they got older. That’s a common practice with aging athletes. So maybe it’s not simply working out that maintains aerobic capacity and therefore, in part, race performances; instead, it is how much training you do and how intensely you do it.

Yes, I realize that I am repeating the same message from earlier chapters in “Fast After 50.” It’s a critical lesson for getting faster regardless of your age.