Social Distancing for Athletes

I am thrilled that others are starting to address the question of social distancing when exercising, especially where aerodynamics and drafting dramatically affect outcomes.

As cited in the above-linked article, published in Cycling News....

"In the absence of headwind, tailwind and cross-wind, for walking fast at 4 km/h, this distance is about 5 meters, and for running at 14.4 km/h , this distance is about 10 meters. Further work should consider the effect of headwind, tailwind and cross-wind, and different droplet spectra"

 Four things about this interest me.

1. 10 meters is ~ 30ft, which is more distance than the 20ft I recommended in my last post.
2. The distance to speed ratio decreases with speed, as 4km/h requires 5 meters distance, but 14.4km/h requires only 10 meters, not 18 meters, as 5/4ths of 14.4 would imply.
3. Humidity is expected to influence distance. (5 micron droplets have a lot of surface area for their internal volume)  
4. Transmission is heavily dependent on droplets for propagation, and being 5 microns, 2X the size of PM2.5, is why masks and HEPA filters will trap most of a COVID-19 viral load.

 The virus itself might be much smaller (btw, smaller particles are caught by diffusion), but the droplet it depends on to infect you will get trapped in ANY HEPA filter.

From Wikipedia...

 Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through—at least 99.95% (European Standard)^[4] or 99.97% (ASME, U.S. DOE)^[5][6] of particles whose diameter is equal to 0.3 μm; with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm.^[7] See the Mechanism and Specifications sections for more information.

COVID-19 droplets are 5.0 micros in size

Again, cross-winds will sweep pathogens away between athletes, but head-winds and tail-winds will not. To point #2 above, I believe it is the amount of air mixed with breath and dispersion of air into a much larger body of air that result in a flattening of the curve as speed increases, where speed is your speed added to the wind's speed. Obviously, speed also reduces your time of exposure, limiting how much viral load you can absorb.Tail-winds are probably the worst of cross, head, tail, because it holds you in the contamination cloud the longest.

When riding alone in a tail-wind and encountering a group riding in a head-wind, remember you will be in their cloud for some time, especially if they are observing ~ 20 meters (65ft) of social distancing at 18-20mph. To mitigate your exposure consider holding your breath for a few seconds. With a closure rate of 35mph (50fp/s) you'll need ~ 1 second for each rider you pass in a paceline, assuming it's a pure headwind. Any crosswind component will reduce this requirement.


When stopped, whether riding alone or in a group, consider stopping on a side street or road where other groups are unlikely to encounter you when riding.

For cycling groups I would recommend breaking into groups of 3, and only regrouping at rest stops, being careful to keep a cross-wind between riders when stopped. Riding in large pacelines of a dozen or more seems reckless given what we now know.

One question I have not been able to answer is what happens to the COVID-19 virus/s in a droplet when the droplet dries up in the wind? I suspect that a mucus droplet protects and sustains the virus and when it dries up COVID-19 immediately starts to degrade and is more vulnerable to deadly UV rays, but I haven't been able to confirm this yet. 

Please be safe, but do get out there and ride to stay healthy. COVID-19 kills by taking your breath away, so keep those lungs and heart healthy!.