How to stay safe and ensure that your workout boosts, rather than suppresses, your immune system

Yesterday afternoon, I went cross-country skiing in the woods near my house in Colorado. It was exactly what my mind and body needed — a break from the nonstop coronavirus news alerts and anxiety cycle.

My impulse to take part in some outdoor exercise was a good one, says Dr. Leana Wen, an ER physician, visiting professor of public health at George Washington University, and former Baltimore city health commissioner. For people who are healthy and symptom-free, “This is a time when we should be taking advantage of the outdoors.”

As we avoid congregating and going to places where we’ll encounter other people, it’s easy to start feeling cooped up. Exercising outdoors is a great way to let off your pent-up energy — as long as you take some precautions: first, to avoid contact with others. And second, to adjust your workout routine to ensure that it boosts, rather than suppresses, your immune system.

“Our data show that physically active people have a 40-50% reduction in the number of days they’re ill with acute respiratory infections.”

How to exercise safely outdoors

You can exercise outside while still adhering to social distancing guidelines. Even under California’s “shelter-in-place” ordergoing outside for a walk or exercise is allowed, as long as you keep six feet apart from other people.

No matter where you live, whether walking, running, or cycling, if you come upon another person on your path, move away to maintain a distance of at least six feet as you pass. Avoid touching things like jungle gyms, parcourse equipment, or gates that could have come into contact with someone carrying the novel coronavirus.

You should definitely avoid group activities, but it’s okay to go biking, running, or hiking with another person if you prevent all physical contact and maintain that six feet of distance from one another the entire time, Wen says. Social distancing takes some practice, so you might periodically need to remind yourself not to pass a water bottle or snack to your companion out of habit. During this pandemic, it is crucial to avoid sharing food, drinks, or equipment of any kind.

Also, don’t allow kids to play on playgrounds or touch objects like railings or playground equipment. Wen has a two-and-a-half-year-old and says there’s simply no way to prevent kids that age from putting things in their mouths. “Children are vectors for diseases. They are not capable of observing hand hygiene,” she says.

The best workouts to stay healthy

The intensity and duration of your exercise should be considered. A body of evidence compiled in a recent review in the Journal of Sport and Health Science suggests that being physically active makes you less vulnerable to getting sick. “Our data show that physically active people have a 40-50% reduction in the number of days they’re ill with acute respiratory infections,” says David Nieman, director of the Appalachian State University Human Performance Lab.

But more is not better. Last year, Nieman published a review that he says indicates “beyond a doubt” that engaging in sustained and prolonged high-intensity exercise (think a long, hard run or multihour endurance event) provokes an increase in stress hormones, inflammation, and oxidative stress. Usually this effect is transient, and you can “snap back and carry on,” he says. But some people are more susceptible to that stress than others, and if you’re under mental or emotional stress, eating poorly, or not sleeping enough, you will become even more vulnerable.

Nieman’s research team recently studied Colin O’Brady’s immune function during the adventurer’s controversial ski trek across Antarctica. Using fingerpick blood drops O’Brady collected over a 28-week period, the researchers measured immune-related proteins in O’Brady’s blood. “He went through an extended bout of high-intensity effort, and we saw a sustained dysfunction of his immune system,” Nieman says.

When there’s a novel virus like Covid-19 and no vaccine or cure available, athletes—yes, athletes—tend to be in the vulnerable category as well, Nieman says. If you’ve been marathon training or preparing for a century bike tour or pushing yourself really hard, doing long training sessions of two or three hours, “you are in the group of immunocompromised individuals,” he says.

And even though your immune system is only temporarily suppressed due to the taxing exercise you just put your body through, “if you’ve been exposed to the new virus and your immune system is down due to the hard effort, you’re at risk,” Nieman says.

There’s a history here, Nieman says. A paper published by Dorothy Horstmann in the Journal of the American Medical Association in 1950 showed that during a 1948 polio epidemic in North Carolina and southern California, patients who had done vigorous exercise, such as riding a bicycle or laboring in tobacco fields, during the first three days of the onset of symptoms were more prone to the severe paralytic form of polio.

One of the lessons here is to avoid vigorous exercise if you’re feeling even a little bit sick.

So what kind of exercise intensity and duration is sufficient to push you from helping your immune system to hobbling it? Nieman says that it’s when the effort is hard enough to force your body to dig deep into its muscle glycogen — the stored sugar that fuels muscles. “In our lab, the stress starts after 60 minutes of intense efforts and gets really bad after 90 minutes,” he says.

Even for elite athletes, now is a time to think more about your health than your fitness.

A good rule of thumb is to limit sustained exercise (greater than 60% effort, which means 60% of your max heart rate) to no more than 60 minutes at a time. One way to do this while still getting in some harder exercise is with intermittent intensity, where you mix some high-intensity efforts with rest or low-intensity exercise. “You get your heart rate up for a little while, then back off,” Nieman says. For instance, you might jog or cycle at an easy pace, then do a few near-all-out 30-second sprints. This approach allows you to improve your fitness while avoiding the immune suppression you get when you don’t back off.

Specific advice for athletes

While the coronavirus pandemic continues, Nieman advises athletes to take extra caution to avoid overtraining. This is not the time to push yourself to your limits, he says. Even for elite athletes, now is a time to think more about your health than your fitness, he says.

Whether you consider yourself an athlete or are just trying to stay healthy, consider regular, moderate exercise a vital part of your coronavirus self-care plan. “We have great data that that kind of exercise is immunoprotective,” Nieman says. But you’ll get the most out of it when you’re taking steps to ensure that your body can recover from exercise and the other stresses in your life. That means getting enough sleep, eating well, and finding ways to manage your stress. If you feel tired, take a rest day, and avoid exercising if you feel even a hint of an illness coming on.

Running outside is one of my favorite ways to release stress, and it’s also favored by public health warrior Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases.

“Getting outside in the day and hearing the birds and smelling the grass is kind of a very pleasing thing for me,” he’s quoted as saying in a Wall Street Journal article that reports the Covid-19 crisis has kept him so busy that he hasn’t been able to get out for his normal lunchtime run. That worries me because we need him to stay healthy so he can continue doing his important work. In this time of danger and uncertainty, we all need to engage in self-care, and exercise is one of the best tools we have to keep ourselves well.

As a science journalist, following the latest Covid-19 news is both part of my job and a source of great stress and anxiety, so making sure I get outside for some fresh air and blood-pumping exercise has become more important than ever as we watch this pandemic unfold.