Be Careful Sharing This Viral Simulation—It Hasn't Been Vetted as a Scientific Study
This is a rapidly developing situation. For the most up-to-date information, check in with your local health officials and resources such as the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) regularly.
By now, you’ve likely seen the Belgian-Dutch “study” on how virtual aerodynamics simulations show that we need to be running and riding a lot further away from each other during this COVID-19 pandemic.
The article Belgian-Dutch Study: Why in times of COVID-19 you can not walk/run/bike close to each other published on Medium, a free public platform that allows anyone to publish and doesn’t require fact-checking, has spread like wildfire across social media, with people zeroing in on both the paper’s title and conclusion:
Keep a distance of at least four to five meters [13 to 16 feet] behind the leading person while walking in the slipstream, ten meters [32 feet] when running or cycling slowly and at least twenty meters [65 feet] when cycling fast. "If you want to overtake someone, it is also recommended to start "pre‐sorting" into a staggered arrangement from a fairly long distance —twenty meters with bicycles, for example, so that you can overtake carefully and at a proper distance by moving in a straight line." Compare it to driving: if you want to overtake, you should also not wait until the very last moment.
It’s super easy to get freaked out when you’re now learning that you need to stay upwards of 32 feet away from a runner and 65 feet away from a cyclist in front of you. In some areas, this is not even possible. But take a deep, socially-distanced breath. This paper is not a vetted study nor a study on disease transmission. And it’s important to take both of those factors seriously right now before potentially spreading what could be misinformation.
To be clear, COVID-19 is extremely serious, and we firmly agree that everyone should run and ride solo, leaving the currently recommend six feet of physical distance between yourself and others plus more when you can. But here’s why you should not let this new article rattle you.
This is essentially a “white paper,” a position paper written by someone with authority on a topic—in this case, a team of engineers and sports aerodynamic researchers from Belgium and the Netherlands—but not a peer-reviewed paper or even a non-peer-reviewed study.
The reason peer review is so important is that it enforces the high standards of the scientific method and ensures that unwarranted claims, false conclusions, unacceptable interpretations, or personal views are not published without prior expert review. Think of it as experts double-checking other experts’ work.
Still, using the animated models and figures generally used to understand the benefits of drafting (riding or running in the slipstream of someone in front of you) for improving performance in elite athletes, the researchers used a computational fluid dynamics (CFD) model to simulate the release of saliva particles from persons walking or running in different configurations to see how many large and small droplets might be left in their wake.
They concluded that being in someone’s slipstream—even within the currently recommended six-foot distance—is risky because of the “droplet cloud” they leave behind.
The problem is that none of this is actually validated, including the CFD simulation itself. In the researchers’ own words: “CFD simulations were performed with Ansys Fluent CFD, based on foregoing intensive validation studies for gas and particle releases at different speed around full‐scale manikins representing human bodies. These validation studies will be reported in the peer‐reviewed scientific publication to appear later.”
In other words, the researchers are saying they have this concept they believe to be accurate, but they haven’t had it validated or peer-reviewed yet. Lead researcher Bert Blocken, Ph.D., of Eindhoven University of Technology, said in a Twitter response that they rushed to share findings because this crisis is a world-wide, urgent situation where people are dying and economies are crumbling.
While the intention was good, other experts including CFD engineers have pushed back on using these models for public health purposes, simply because these models aren’t the correct tools for this type of research.
Computer simulations may be fine to show how much air resistance you might face in a group ride or race situation, but they can be flawed in terms of microbiology, says Rebecca Lewandowski, Ph.D., biologist at the Biomedical Advanced Research and Development Authority under the Assistant Secretary of Preparedness and Response within the Department of Health and Human Services.
“Personally as a biologist, I’ve never seen a computer be able to mimic the innumerable variables that occur in biology,” Lewandowski told Bicycling. “I’m skeptical about something simulated let alone not peer reviewed.”
When we asked Lewandowski if, as a recreationally competitive cyclist and runner herself as well as a biologist, she found anything new worth considering here, her answer was simply, “Zero.”
To be fair, Blocken has been clear that their work is aerodynamics and not virology. In another Twitter response, he said, “The droplets evaporate very fast. Question is what happens with virus on solid nucleus: still effective to infect? Some argue yes (other white paper), I doubt it. Infection rates would be even much higher.”
That is to say, once the droplets evaporate in the air, can the virus still infect you as it lingers as a dried out particle in the air? An analysis of more than 75,000 COVID-19 cases in China, haven’t found that kind of airborne transmission.
We get it. These are scary, stressful, uncertain times when news changes by the day if not by the hour. Nobody wants to be cavalier, and we’re all looking for answers. But it’s important to not hurriedly take one piece of incomplete evidence and fill in the blanks based on speculation.
In the end, the advice still stands: Stay home as much as you can. Wash your hands often. Ride and run solo, striving for as much physical distance as you can from others—but definitely at least six feet. Wear a buff or bandana if you’re going to be in highly trafficked areas. If you feel at all sick stay home.
This isn’t the time for group rides or drafting. If this current paper does anything, it reinforces that. There is also no harm in holding your breath as you pass people, giving tons of room, and staying well out of anyone’s slipstream. The harm can happen when people take papers like this and draw wide-sweeping conclusions like we shouldn’t run or ride outside (which the researchers themselves have not done, but others in social media have), which is well-known to have important mental and physical health benefits.
The bottom line: We should all be careful about the news we spread as we try to prevent the spread of this disease.
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