Causes of Marathon Flu
Athletes who take part in strenuous endurance exercise may experience depleted immunity, with “arduous bouts of exercise” linking to increased symptoms of upper respiratory tract infections. This response could be due to several factors, including environment, genetics, physical and mental stressors, and underlying health conditions.
Ian McKeag, MD, an associate professor of family and community medicine at the University of Alabama at Birmingham’s School of Medicine, explains how strenuous exercise (like running 26.2 miles in one go) affects the body.
“When you’re running a marathon — or even a half-marathon — you’re putting yourself through a lot of physical demands,” he says. “You’re burning all sorts of energy, expending glucose and glycogen, and the body is only really equipped for about an hour before it starts to pull from other sources. As it starts to pull from some of those sources, that puts more demand on the body as a whole.” Immunity dips, leaving you at risk of getting sick.
There’s also a lot going on with your hormones during training that can cause issues.
“When you’re training for a marathon and persistently putting the body in that kind of stress, things like cortisol levels change,” says Dr. McKeag. “That stress hormone can have a negative impact on your immune response [and can be] one reason the immune system isn’t as strong after running longer distances.”
Another big factor is exposure to germs.
“On the day of the race, runners are put into a corral packed with other runners, and there’s a bottleneck for the first few miles of the race,” says McKeag. “You’re going to be exposed to a big, diverse group of people.”
Coviello agrees, noting that you can also be exposed to infectious bugs while traveling to a race.
“And in the race, when your immune system is already compromised, you’ve got all these germs that are around you,” she says. “Then you’ve got people throwing snot rockets all over the place. And at the end of the race, you’ve got all these snot- and sweat-filled bodies, and everybody’s hugging each other.”
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