Exercising is one of the few things we’re still allowed to do in quarantine, but it may carry more risks than anticipated, a team of Belgian and Dutch researchers warn.
However, there are many issues with this analysis. For starters, the researchers chose to bypass standard scientific publishing, detailing only their findings and not their methodology or how the results were reached.
When it comes to understanding how a disease is transmitted, it’s not just about medicine and biology. For instance, material scientists can help us understand what face masks offer better protection, and engineers can find new ways to improvise ventilators that can save people’s lives. Similarly, aerodynamicists can help us understand just how the disease gets passed around from one person to the other.
The reason why aerodynamics is so important here is that SARS-CoV-2, the virus causing COVID-19, is passed through droplets. If we want to understand how it is transmitted, we first need to understand how these droplets can be transmitted in day to day situations.
In a simulation that is admittedly preliminary, unproven, and not peer-reviewed, a team of aerodynamicists presented new findings that suggest such droplets can easily be passed over a distance longer than the usually-recommended 1.5 meters — especially if you’re walking, running, or cycling.
“If someone exhales, coughs or sneezes while walking, running or cycling, most of the microdroplets are entrained in the wake or slipstream behind the runner or cyclist. The other person who runs or cycles just behind this leading person in the slipstream then moves through that cloud of droplets,”says Bert Blocken, professor of civil engineering at Eindhoven University of Technology and KU Leuven
There is much to be said about this analysis — including the fact that we don’t really know how reliable it is, how, exactly, the results were obtained, and why it was published in the manner it was. We’ll get to that in a bit.
What the simulation showed
The researchers simulated the occurrence of saliva particles an average person would generate during movement (walking and running), and in different positions, simulating it with specialized algorithms.
This type of study is routinely used to help athletes improve their performance level or deploy a position that is more aerodynamic. But it can also reveal how droplets pass through the air.
The simulations showed that when people walk or run side by side in calm weather, the droplets tend end up behind the two, and there is little risk of contamination.
The greatest risk of contamination is when people walk or run behind each other, in each other’s slipstream (the region behind a moving object or person in which a wake of fluid is moving at velocities comparable to the moving object).
Furthermore, when you’re overtaking someone (whether it’s through walking, running, or cycling), you need to be sure that first of all, you don’t stand behind that person’s slipstream, and after you overtake them, you don’t put them in your slipstream.
A good way to think about it is: you need to overcome someone the same way you’d do if you were driving a car. Get on a different trajectory early on, leave a healthy gap, and don’t wait until the last moment (that’s a good idea in general, not just in a pandemic).
Based on the results, Blocken advises keeping a distance of at least four to five meters behind the leading person while walking in the slipstream, ten meters when running or cycling slowly, and at least twenty meters when cycling fast.
Blocken hasn’t published his study or his methodology yet. We don’t know exactly how the results were obtained and how the slipstream itself was modeled — and there are big questions to clarify.
For instance, a 2016 MIT study found that sneezing doesn’t produce a simple spray of particles, but rather a complex fluid cascade, and therefore needs to be modeled accordingly. What does this mean for heavy breathing? We don’t really know, and it’s a problem.
There is also the matter of designing the flow of the particles: if a simple simulation starts from the nostrils, it is probably missing out an important part, as the particles actually start out in the lungs and this affects their journey out of the nostrils. Did this simulation start in the lungs or in the nostrils? We don’t know. There are plenty of good simulations on sneezing and breathing, but it’s a very complex procedure that needs to be justified thoroughly, writes Stephen Ferguson, a Computational Fluid Dynamics Engineer in a scathing post.
So it’s hard to say just how reliable the sneezing and coughing simulations are, especially when also considering the virology aspect. In normal times, no scientist worth his salt would have published this type of simulation without offering the details.
But these are not normal times.
Scientific publishing takes months and months, and while medical journals have greatly accelerated that process, we’re not sure if the same happens for aerodynamics journals.
We’re facing an urgent situation. It’s more important than ever to bring science to the public quickly — but it’s also important to ensure that we don’t get any bad science out there to confuse things even more. The thing is, at this moment, there are many specifics we don’t know about this study, and while it’s important to get this type of science out, it’s also important to look at how the data was obtained before we start making any recommendations for policymakers or joggers.
The bottom line is that it’s understandable that researchers from all fields want to help. We need this type of study, and we need to better understand how the coronavirus can spread, but we also need rigorous evidence.
It doesn’t hurt to leave a bigger gap between yourself and other walkers or runners. Does it reduce your risks of contracting the disease? We’re not sure. But it’s harmless, and at the very least, it might make you feel a bit safer going outside — and that’s something all of us need at this moment.