Avoid the Slipstream When Walking, Running, and Cycling

Many people have taken to walking, running, and cycling for the benefit of mind and body during the COVID-19 pandemic, and many engage in those activities with others. New, unpublished research coming out of the Netherlands and Belgium suggests that 2 or more people walking, running, or cycling right behind one another should leave much more than 6 ft of space between themselves.

Using animations developed from computational fluid dynamics models, the researchers showed that a cloud of emitted respiratory droplets is entrained in the slipstream–the wake behind any moving person that pushes air slightly behind them–even when he or she exhales normally. People cycling in groups often use the slipstream of the person in front of them to reduce air resistance, but smaller slipstreams also form behind anyone who is walking or running.

Admitting that much more needs to be learned about the coronavirus-infection risk posed by such slipstream-carried droplets, the authors show that when someone walks through the droplet cloud left by the person in front of them, droplets can stick to the following person’s body.

So how far back should you be from the person in front of you when you are out doing these things? The authors recommend the following distances:

  • 13 to 16 ft (4 to 5 meters) while walking
  • 33 ft (10 meters) when running or cycling slowly
  • 65 ft (20 meters) when cycling fast

These preliminary findings suggest that exercising side by side may be safer than exercising one behind another, but doing so is often not practical or safe, especially when cycling on public roads.

Although these data are unpublished, in their white paper the authors said, “We decided it would be unethical to keep the results confidential and keep the public waiting months for the peer review process to be completed.”

OrthoBuzz would like to thank Dr. Freddie Fu, Chair of Orthopaedic Surgery at the University of Pittsburg Medical Center, for bringing this research to our attention.

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