If you've started running, or gotten back into it, in the last few weeks, you're not the only one.

Cities across the country have seen a surge in the number of people running, walking and biking outside as social distancing guidelines take hold.

As more people turn to running, there are a lot of questions about how to do it safely. We talked to researchers and runners alike to answer some of the biggest questions.

6 Feet Is Not Enough

For starters, national experts aren't telling people to avoid exercising outside — even if you're under a shelter-in-place mandate. Health experts say your risk of infection from outdoor exercise is low.

You do have to practice social distancing. The Centers for Disease Control and Prevention recommends that you stay at least 6 feet away from other people when you're outside your home.

But that may not be enough for runners.

New research suggests that standard social distancing guidelines might be insufficient to stop the spread of the virus when it comes to strenuous activities.

Linsey Marr, a professor of civil and environmental engineering at Virginia Tech with an expertise in airborne disease transmission, says that 6 feet may not be enough.

"If you're running and you happen to be infected, you might release more virus into the air than if you're walking because you're breathing harder," Marr tells NPR.

But by moving fast, you're also disturbing the air around you and effectively diluting the virus, says Marr. This makes it hard to determine whether there's a greater risk of spreading the virus if you're running versus walking.

Regardless, Marr says runners can reduce the risk of transmission by staying farther apart from other people than the recommended 6 feet. She suggests that runners increase that distance to at least 10 feet, and other experts have suggested doubling CDC guidelines to 12 feet.

Maintaining this level of distance requires that runners not only run alone, but run far away from other people. Runners should avoid places with high pedestrian traffic or run at off-peak times like early in the morning or late at night.

Last week, for instance, Paris banned running, and all other outdoor sports, between 10 a.m. and 7 p.m.

To Mask Or Not To Mask?

Another question on runner's minds has been whether to wear a cloth face covering.

The CDC recommends wearing cloth face coverings in "public settings, where other social distancing measures are difficult to maintain" in order to avoid community-based transmission of the virus.

So just as you'd wear a mask to the grocery store or pharmacy, you should wear one if your run is likely to bring you into close contact with other people.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has noted that as many as 50% of people who have the virus may be asymptomatic. Runners who feel well enough to go on a regular run may still be infecting those they come into contact with.

According to the CDC, your mask should fit snugly over your nose and mouth, which can be difficult to maintain while running. Some runners use neck gaiters — a tube of fabric, usually moisture-wicking — to cover their mouth and nose in lieu of a mask.