Ed Kornoelje DO
Sports Medicine|University of Michigan Health-West

Last month we looked a bit at race safety, particularly around heart health. This month: atrial fibrillation (AF) and endurance athletes—is there a problem?

Let me start off by saying that running and endurance training are very good for the heart, general health, and longevity. Multiple studies over many years show those who exercise have lower a risk of cancer and heart disease, live longer, have stronger bones and muscles—are just healthier. So exercise away—right?

Mostly. In the last few years several studies have come out asking: can there be too much of a good thing? One article looked more at general health and life expectancy studies, a few of which suggested that those who ran or exercised more had a similar mortality rate as those who did not exercise at all—exercise was better for us to a certain point, but the more we exercised the more we returned to where we started. Some of these studies were not well constructed and did not have enough “high exercisers” to reach that conclusion. They also did not meet the eye test—while bad things can happen to anyone, those who exercise a lot for a
long time are living longer. Since then, multiple studies (with higher numbers of heavy exercisers) have shown that while there may be a point at which health gains level off (or perhaps start to be lost), this is a very high level, and we are much healthier even if we push the limit compared to those who do not exercise. A couple of my conclusions based on the article:

1. While running for cardiovascular health is a great idea, it impacts many other systems as well. It is no secret that running improves mental and physical bodily
functions, not just the heart.

2. From the health perspective, there likely is a middle ground. Why would running be different than most everything else? When reviewing many studies this appears to
hold true: for example, running lowers your risk of arthritis to a certain point—after a certain point the risk may go up a bit (but you are still better off than those who do
not run). There appears to be some heart muscle damage in those who train for marathons, but again, going past the middle on the “too much” side is far better
than doing nothing at all.

I came across a study from 2020: “The counterintuitive role of exercise in the prevention and cause of atrial fibrillation” from the American Journal of Physiology. The mini-review does a nice job of describing AF, it’s incidence in the general population (it is the most common cardiac arrhythmia affecting more then 33 million people worldwide), and the fact that physical activity lowers the incidence of AF (25% of new cases may be attributable to the absence of physical activity and tripling the 150 min/week of moderate physical activity guideline decreases risk of AF by up to 20%). That’s 450 minutes per week—7.5 hours—of moderate intensity exercise per week. And we only “need” 75 minutes per week of vigorous physical activity. If we mix that in, we get to our “needed” physical activity amount with fewer minutes—how does this affect the upper limit? In any event this is quite a lot of activity, but, as the reader pointed out to me, easily attainable when training for a marathon or something similar. If a runner runs 40 miles a week at various intensities, and their average pace is 10 min/mile (round number) we are at 400 minutes of activity with some of it being vigorous—already at or close to the level we know appears to decrease the risk of AF. But what if we run more, add other activities, stand at work, park a long way away from the door to add steps to our day…? Is this too much?

The honest answer is we are not sure. The 2020 article goes on to note a few studies around runners, cyclists and cross-country skiers that show a higher risk of AF in those who exercise “more.” From the article “defining the dose of exercise associated with potentially detrimental effects on the primary and secondary prevention of AF is challenging and importantly limited by a lack of prospective studies that objectively report exercise volume and AF occurrence” and there are “research caveats relating to trial design and sample size, for example the relatively small participant numbers at the highest of activity levels.” There is some indirect evidence
that high, high volumes seem to be detrimental, but no direct studies showing this.

So where does that leave us? My thoughts:
1. AF is the most common arrhythmia in the general population and the risk increases as we age.
2. Exercise, even high intensity exercise, well over the recommended amount is safe and actually reduces the risk of many diseases including AF.
3. Erring on the side of too much rather than too little may increase risk very slightly for AF but appears to make us healthier in general.
4. High intensity training improves VO2 max which helps us live longer better, even though it stresses the heart.
5. Most of us, even if we are avid and regular exercisers, stay in or very close to the range that has been studied which does lower risk for AF.

If you want to find a physician to help with medical or musculoskeletal issues, we can help. Sports Medicine at University of Michigan Health-West has seven Primary Care Sports Medicine Physicians all over West Michigan. Being trained in family practice as well as sports medicine means we can treat any and all medical issues, take care of injuries, and serve as your primary care physician. For a list of physicians, services, and locations give us a call at 616-252-7778 or check us out at www.uofmhealthwest.org and search “sports medicine.” We are also continuing Injury Wise at Gazelle Sports in Grand Rapids every Wednesday from 5:45-6:45 PM—check with Gazelle for specifics. Open to athletes of all sports and ages, it is an opportunity to get some info on injuries and training or just say hi!