Science, Exercise, and Covid-19
The main purpose of science is to predict the future, based on what is already known. In the context of the Corvid-19 pandemic, the predictions requested of scientists may be narrow or broad. "Will I catch Covid-19 from someone I'm running or biking with in the open air?" is an example of a narrow question. "How many will die of Covid-19 if we do ______?" is a very broad question.
The answer to the narrow question of the risk of contracting Covid-19 while exercising is remarkably tricky--and tricky is frustrating for humans. By our very nature, humans want answers that are certain. It is this quest for certainty and simplicity that gives rise to reasonable, simple recommendations like the specified six foot spacing of "social distancing."
The best answers scientists can provide are subject to modification based on new data. In the early stages of the Corvid-19 pandemic in the United States, wearing a mask was not thought necessary as long as six foot spacing was maintained. That prediction, based, I believe, on ideas about droplet spread in normal conversation, was dashed by the unintentional and unfortunate experiment conducted by the Skagit Valley Chorale in March [See Airborne Spread], where 45 of 60 participants fell ill with Corvid-19 and two died in the weeks following a 2.5 hour choir practice, a choir practice in which members someone nervously complied with hand-washing and social distancing recommendations then in effect. In no small part due to this new data, the recommendation changed from no mask necessary to, "Wear a mask!" [even as our White House resident declared, like a rebellious child, that he wouldn't wear a mask and that compliance was "voluntary"--never mind that the White House now uses a rapid test that screens all visitors for Covid-19, a test unavailable to the general public].
The CDC recommendations around masks changed in response to new evidence. That's how science should work.
So can I catch Covid-19 when exercising without a face mask with proper distancing, especially if I'm outside? The answer, as is usual in science, is, "Maybe." There are some reasonable ways to be more careful.
First, understand that we have no documented evidence of Covid-19 spread from one exerciser to another. That would be hard to detect and document, after all. One hopes there is no Skagit Chorale-like experiment unwittingly performed among runners and bikers. However, without such an awful experiment (the infamous Tuskegee Airmen experiment comes to mind), quite a lot is known about the basic physics of droplets and aerosols, coughing, sneezing, and breathing that can be hypothetically applied to the question of disease spread.
I'll give you the punchline first, but if you want to understand the scientific basis for the recommendation read on.
On the basis of these results the scientist advises that for walking the distance of people moving in the same direction in 1 line should be at least 4–5 meter, for running and slow biking it should be 10 meters and for hard biking at least 20 meters.
The quote is from an article that appeared in Medium.com (a very good, but not always, reliable source--read their disclaimer) "Belgian-Dutch Study: Why in times of COVID-19 you should not walk/run/bike close to each other." Please check it out. The illustrations are impressive and memorable. The other impressive thing about the article is the science upon which it was based,
"Towards aerodynamically equivalent COVID19 1.5 m social distancing for walking and running." If you want a window on the kind of understanding of physics upon which this recommendation is based, click and have a look.
So are these recommendations hard and fast, fully "ready for primetime"? Of course not, like all science, the hypothesis that one could catch Corvid-19 from biking too close behind an infected but asymptomatic biker is subject to further investigation. Even so the hypothesis, the prediction, is reasonably presented and bolstered by the underlying knowledge base.
As with all scientific hypotheses many questions remain. Is the dosage of virus particles suggests might be delivered sufficient to transmit disease? What is the actual risk number? Has anyone actually caught the virus in this way under real world circumstances? Answers to these questions may never be known, but in the meantime, I'm going to be a little more careful when I'm exercising in the open air.
Keep to the high ground,
P.S. The CDC "Recent Studies" section under the new face mask recommendations all concern disease spread from asymptomatic carriers documented in peer-reviewed medical literature. They do not list a reference to the Skagit Chorale cluster. As far as I know a formal epidemiological study of that incident has not been done or published, except for fairly detailed and compelling coverage in the mainstream media.