Linsey Marr, an expert in airborne transmission of viral diseases and a professor of civil engineering at Virginia Tech, says the issue of whether people can become infected from cyclists or runners is still undecided. “We need to keep in mind, though, that we don’t yet know what size particles released by an infected person actually contain virus and whether that virus is ‘alive,’ or can still infect others,” Marr wrote in an email to WIRED.
She agreed with Blocken’s advice to walkers and runners to allow for greater spacing if traveling right in front of or right behind another person. However, she notes that the study assumed no wind. “Basically, if you’re directly upwind or downwind of others,” Marr wrote “allow for more space.”
Marr wrote that she wasn’t upset that the researchers decided to publicize their work through the media instead of through the traditional route of submitting the study to a peer-reviewed journal. “Given the situation we’re in, I think it’s fair that the researchers shared the results because they could be immediately useful,” she wrote.
A half dozen other virologists contacted by WIRED declined to comment on Bracken’s study, saying they were busy reviewing papers or conducting their own research, or had responded to reporters’ requests last week. But as many researchers in this field had previously told WIRED’s Roxanne Khamsi, there’s still a vigorous debate among researchers over how likely the virus is to spread through air. Some argue that if it’s spread through larger blobs or “droplets” that are coughed, sneezed or exhaled, it will fall quickly to the ground; others argue that if it is spread through finer “aerosols” it can linger aloft for much longer, creating a higher infection risk. And some say there’s no clear division between the two categories, anyway.
In the meantime, experts say it’s still a good idea to exercise, and that it makes sense to distance as much as you can, whether that means avoiding crowded spaces or using technology as a way to exercise in the (remote) company of friends. Anne Hyman, a commercial laboratory scientist and president of a Washington, DC-area cycling club, is concerned about the potential risks of spreading Covid-19 while riding. “People are taking to wider areas to walk and congregate, and it’s creating a dense situation on multiuse paths,” said Hyman, president of the 2,000-member Potomac Pedalers Touring Club. Instead, she rides her stationary bike with friends using the Zwift virtual competition software that allows users to race against each other. The triathlete hasn’t ridden on the roads near her suburban Maryland home since the state was put on a lockdown March 30.
Experts are also reminding the homebound that 30 to 60 minutes of daily exercise—even when done alone or inside—boosts the immune system. “We do know that the number one objective is to reduce exposure,” says David Nieman, an exercise immunologist and director of the human performance lab at Appalachian State University. “But I believe it’s possible while we still get our physical activity.”
Nieman, a marathon runner, has reviewed Blocken’s study and agrees with the concept of keeping a bigger buffer zone between fellow runners or riders. “You can say I’m going to go with one or two buddies who I know well and claim they are not sick and just trust that it’s OK, but it’s not foolproof,” Nieman says. “People you know and trust may have been exposed. Instead, try exercising outside by yourself. The risk is extremely low, and all the benefits are there.”
WIRED is providing free access to stories about public health and how to protect yourself during the coronavirus pandemic. Sign up for our Coronavirus Update newsletter for the latest updates, and subscribe to support our journalism.
More From WIRED on Covid-19