When it Comes to Walking and Running, Six Feet of Distance Might Not be Enough

May 22, 2020 by
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In recent weeks, experts around the world have suggested six feet in the United States (1.5 meters elsewhere) as the magic distance in order for people to space themselves apart to reduce the spread of the novel coronavirus. Some countries have even put it into law.

However, a Belgian-Dutch Study published as a white paper in April discovered when it comes to running and walking, six feet between people isn’t far enough.

Understanding micro-droplets: Recent COVID-19 research has shown that the virus can spread through our saliva.

  • When we cough, sneeze or exhale from a breath, we release droplets, or sometimes micro-droplets that are too small to see. If we’re infected with the virus, these droplets can infect a person who inhales them, or gets them on their hands and then touches their face.
  • Luckily, these micro-droplets fall to the ground or evaporate within six feet (1.5 meters). At least, this is the case when we’re standing still.
  • When we’re moving, via walking, running, and cycling it’s a whole other ball game, explained Chris Hinshaw, the world-renowned endurance coach who has coached dozens of CrossFit Games athletes.

Hinshaw has digested the April white paper in depth in order to provide advice to his athletes about how to stay virus-free and continue to run outside. He offered Morning Chalk Up some key takeaways to “inform and minimize potential risk” to runners, or even walkers.

Walking versus running safe distances: If you’re walking, the study recommends keeping 15 feet (five meters) of space between you and another walker. And if you’re running, 30 feet (ten meters) is recommended. The Belgian-Dutch research team discovered this by assessing the rate a person is moving and how it affects the flow of the airborne particulates.

  • “Although there are many other factors to consider, this study observed this to be a safe distance when you’re walking at a speed of two-and-half miles per hour (4 km). And with running, 30 feet (ten meters) was found to be safe at a running speed of nine miles per hour (14.4 km). So way more than the six feet (1.5 meters) we have been told,” Hinshaw said.

The worst place to run: Walking directly behind someone else, where you’re clearly in their slipstream, meaning directly in their micro-droplet path, is the most high-risk place to position yourself.

  • “You can see here that if you’re walking directly behind a walker, and you are two meters away, you are completely enveloped in airborne particulates walking at a speed of 4 km an hour,” Hinshaw said.
This diagram comes from the white paper and illustrates the micro-droplet slipstream behind a runner. (Photo credit: Towards Aerodynamically Equivalent COVID19 1.5m Social Distancing for Walking and Running)

It’s much safer, on the other hand, to walk or run to the left or the right of the person ahead of you, he added.

  • “So if you’re catching up and are about to pass a runner or walker, you should move to the side well ahead of time,” Hinshaw said.

Consider wind patterns: One of the shortcomings of the study was that it didn’t factor in wind, which can have a huge impact in where airborne matter blows.

  • “Further work should consider the effect of headwind, tailwind and crosswind, and different droplet spectra,” the white paper stated.

To understand just how much wind can affect particulate matter in the air, Hinshaw pointed to Eliud Kipchoge’s now-famous sub-two-hour marathon in October 2019. He was the first man ever to run the 26.2 miles in less than two hours, completing it in a time of 1:59.40, meaning a 4:35 mile pace. Kipchoge’s time, however, is not recognized as a world record, because he used a rotating group of pacer runners, who strategically shielded him from wind throughout his run.

  • “They use various formations depending on where the wind was, and it hugely affected his time. The point is, the aerodynamic effect from the wind makes a huge difference in terms of where the airborne particulates are going,” Hinshaw said.

Ultimately, this means runners should pay attention to not just being 30 feet (ten meters) behind and off to the side of another runner, but also to consider whether you’re running in a tailwind, a headwind or a sidewind, and adjust their paths accordingly, Hinshaw said.

Not without its critics: While Hinshaw has used the study to help inform individuals assessing the health risks of walking or running outside, the study itself isn’t without opposition.

  • A Vox article points out that the European study “contained no input from epidemiologists or virologists and was not peer-reviewed,” adding, “Its logic is deeply flawed.”

Interviewed in the article is the virologist Angela Rasmussen, who pointed out that in order to contract an infectious disease, a “minimum infectious dose of the virus” must be met, and the study failed to consider how many virus-infected particles a person must inhale in order to become infected.

It’s better to be extra safe, Hinshaw said about the opposition.  So he will continue to err on the more conservative social distancing side in the face of a worldwide pandemic, he explained.

  • Hinshaw asked rhetorically: “Are the distance recommendations excessive if they enable people to safely  go back outside and regain their health and fitness?”

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