Health Risks Associated with Ultramarathons

Running, even extremely long distances, can be done with minimal long-term health impacts for most people. Here’s what to know about the risks associated with running ultras, according to experts.

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If you visit the finish line of any ultramarathon, you could easily conclude that such races are unhealthy. Exhausted runners, blistered feet, and busy medical tents aren’t uncommon. 

We know that regular physical activity has a range of benefits, from reduced disease risk to improved brain health. But ultramarathons aren’t necessarily “regular physical activity,” and recent research suggests that they can actually have long-term risks. These negative health outcomes can sound alarming. However, according to experts and current evidence, most people can safely participate in ultramarathons with smart training and racing habits. 

Cardiac Concerns

According to Nick Tiller, an ultramarathoner and researcher at Harbor-UCLA Medical Center, the largest area of concern about ultrarunning’s potential long-term risks is the heart. This is because the cardiovascular system is both easily altered by activity and essential for health. 

Tiller recently co-authored a review of the potential long-term implications of ultra-endurance races. First among the concerns? Maladaptation of the heart. 

Competing in ultramarathons requires significant amounts of training that forces the body to adapt. The changes–such as the increased capillary density that allows for more blood delivery to muscles, or the increased blood delivery with each heartbeat that allows for greater efficiency–improve your ability to run. 

“All of these things are favorable, but the downside is, because the cardiovascular system is malleable, you can have negative responses as well,” Tiller says. These negative responses are well documented. Lifelong runners have an increased risk of developing predictive factors for cardiac disease and death, such as atrial fibrillation (an abnormal heart rhythm) and myocardial fibrosis (scarring on the heart). Similarly, runners can develop right ventricle dysfunction (the right ventricle of the heart loses efficiency) and a buildup of coronary artery calcium (calcium-rich plaques in the arteries). 

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These adaptations are found in a large portion of endurance athletes. The prevalence of atrial fibrillation among endurance runners and professional cyclists has been found to be five times greater than in other groups. Research published in the journal Circulation found that more than 50 percent of endurance athletes exhibit right ventricle enlargement. Other studies have found elevated plaque levels in roughly 50 percent of high-exercising participants. 

If this all sounds alarming, there’s good news. According to Tiller, there is some evidence to suggest that high levels of aerobic fitness and large training volumes don’t actually put you at increased risk of mortality. In fact, one study concluded that high training loads and the associated increase of coronary artery calcium (CAC) do not appear to increase risk of mortality or cardiac disease. Another more recent study found that, even though people who trained at higher volumes had higher CAC levels, they did not suffer more adverse effects than those who exercised less. 

“I want to be very clear that running is healthy, more so than not being a runner,” says Dr. Mark Harrast, a sports medicine physician at the University of Washington and the medical director of the Seattle Marathon. He has published research on optimal levels of exercise for cardiovascular health. “We just don’t know what the limit [of healthy exercise] is. But with the limited evidence we have, it looks like there may not be a definite limit. It may not be better to do more, but it may not be worse either.”

High levels of training absolutely cause changes to the heart. Some of those changes may be associated with negative outcomes, but the important question is whether they actually lead to health problems and increased mortality. Harrast says there is not enough data to provide a conclusive answer, but increasing evidence suggests that there isn’t a clear point where the benefits of running are outweighed by potential risks. 

The takeaway? If you’re healthy, it’s likely safe to keep on training

Kidney Damage

The heart isn’t the only part of the body affected by ultramarathons. The stress of a race affects multiple body systems. One of the most common race-day health risks is acute-kidney injury (AKI), an episode of kidney failure. During exercise, there is less blood flow to the kidneys, and as a result, decreased kidney function. Often, AKI is exacerbated by high temperatures, dehydration, and anti-inflammatory ingestion; it is commonly observed among both marathoners and ultramarathoners. 

These injuries are short-term ailments, and often resolve within a few days. However, repeated AKI has been linked to a higher chance of developing chronic kidney disease. Just how strong that link is, and how much ultrarunners are at risk, is unknown. 

During a race, the most common advice to mitigate the risk of AKI is to follow current guidelines for fluid intake and salt replacement. “After a race, there are a lot of things that are concerning, including acute kidney injury becoming more chronic kidney injury,” says Harrast. “You need to recover before you start pounding the pavement or start pushing too much.” 

Bone and Muscle Damage

Many runners are concerned about joint damage, and for good reason. Musculoskeletal injuries are common among endurance athletes. These can range from stress fractures to muscle tears to tendonitis. Roughly 90 percent of injuries that ultra-endurance athletes suffer are overuse related, according to a study published in Sports Medicine. This makes sense, considering the high training volumes necessary to complete these events. While low to moderate levels of running have been linked to increased bone strength, higher volumes can have the opposite effect. 

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There is some evidence that something similar happens with the development of osteoarthritis in runners. “When you’re not running at all, you have a higher level of arthritis. If you’re a mild to moderate runner, your chance goes down. Those levels of running are actually effective for preventing arthritis,” says Harrast. However, with higher volume runners, the data isn’t as clear, but “it does suggest that there is more arthritis in that population.” He emphasizes that most people should not avoid running for fear of developing arthritis. 

For runners who are concerned about developing osteoarthritis, Harrast recommends an individualized approach, as certain factors can make a person more likely to develop osteoarthritis. These include previous knee injuries and family history. Runners can consult their doctor or physical therapist to develop strength training programs designed to help prevent development of osteoarthritis, and should be careful with increases in training volume and recovery.

Youth Participation

Most experts agree that ultramarathons are not for adolescent athletes. “We know that young athletes, under 16, really should not be participating,” Tiller says. Youth athletes who do participate in ultras tend to get injured more often than their peers, are more injury prone in adulthood, and often do not continue to participate in ultra-endurance events. 

Harrast concurs. “For longer distances like the marathon and up, waiting until late high school, if not later,” is recommended. He emphasizes that any participation must be youth-driven, and higher training volumes should not be the result of parental or coaching pressure. The stress on the body is excessive, the training levels necessary to perform well are likely too high, and the risk of burnout is increased. Thus, many experts recommend discouraging youth single-sport specialization until after puberty. 

Mitigating Risks

The stress of racing is evident throughout the body following a race. “You’ll get a big change in the body. You’ll get a big decrease in lung function, a big decrease in heart function, a big increase in inflammation,” says Tiller. Most of these changes resolve within a few weeks. For the most part, in intermittent doses, they are nothing to worry about. But Tiller, who recently turned 40, is concerned about the long-term implications of repeated exposures to these stresses, and has changed his racing habits accordingly. 

“Knowing the literature as I do, I’m much more conservative now with my running. I used to race between three and five ultras a year, but these days I’m more selective, particularly as I get older,” he says. The time between races allows the body to recover.

Just how long to take between races will vary between individuals. Tiller suggests at least a few months between ultramarathons, but this will vary depending on distance, effort, and other similar factors. 

Similarly, here’s Harrast’s biggest advice to would-be ultramarathoners: “Respect the distance and make rest a part of your training regime,” he says. He emphasizes that recovery is essential both in training and after races. “Really, this just means pay attention to your body. Don’t run through injury and pain. Don’t try to push when you’re not ready to.” 

Harrast says runners should try to get good sleep, nutrition, and take care of any musculoskeletal ailments. Whether that is through massage and myofascial work or cross training and off-days, recovery is essential in increasing health and longevity in the sport. Similarly, following an individualized training plan that is tailored to you can improve racing results while promoting recovery and mitigating risks of overtraining.

So, are ultramarathons safe? For the most part, yes. With informed decisions about which races to do, how often to race, and how well you are recovered, most people can participate in ultramarathons without negative outcomes. Running is good for your health and ultramarathons can be a fun way to challenge yourself and compete with like-minded people. 

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