New Social Distancing Recommendations For Runners and Cyclists
Bert Blocken, a Professor of Civil Engineering at KU Leuven and a Specialist in Urban Physics, and Sports Aerodynamics is recommending new distancing guidelines for outdoor activities and sports from research conducted by universities in Belgium and Netherlands into slipstreams of runners and cyclists from exhaled droplets in wind tunnels.
WHAT DO WE MEAN BY SLIPSTREAM?
A slipstream is a region behind a moving object in which a wake or current of fluid (typically air or water) is created and travels behind at high speed. In this case, we refer to a slipstream as a surrounding path of perspiration that is caused by a runner or cyclist.
IS 2 METRES APART ENOUGH?
It was concluded that the typical guidance to keep 2m apart is “very effective” with limited movement; either indoors or in calm weather. Although, inadequate when exercising in the direct path of other members of the public.
The paper, entitled Social Distancing v2.0: During Walking, Running and Cycling, found that walkers should keep at least 4 metres clear when directly behind others, runners should stay 10m from one another, and fast cyclists should ride as much as 20m apart, in order to avoid passing through “droplet clouds” from others exercising.
Professor Bert Blocken added: “If you want to overtake someone, it is also recommended to start ‘pre-sorting’ into a staggered arrangement from a fairly long distance – 20m with bicycles, for example, so that you can overtake carefully and at a proper distance by moving in a straight line.”
THE DANGERS OF DROPLETS
Professor Bert Blocken has stated, “if someone exhales, coughs or sneezes while walking, running or cycling, most of the micro droplets 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.”
“People who sneeze or cough spread droplets with a bigger force, but also people who just breathe will leave particles behind”, said Blocken. "The biggest particles create the highest chance of contamination – although they fall down faster, when running through a cloud of them, they still can land on your clothing,” he said.
RECENT CRITISM OF THIS RESEARCH
However the white paper, published by Eindhoven University of Technology and KU Leuven in Belgium, came under some criticism, as it has not yet been peer reviewed. Blocken said the paper was rushed into the public domain because the authors considered it “unethical” to hold back potentially life-saving information from the public for any period of time.
Professor Blocken defended his research by stressing that aerodynamic experts carried out this research, rather than virologists, and so only the likelihood of someone passing through a “particle cloud” was evaluated and never claimed to assess the actual risk of infection or include viral load analysis.
Speaking to The Independent, Professor Blocken defended his research, saying: “Some people think this all comes out of the blue, but these are experiments I’ve been running for 20 years.
“It’s interesting to see studies can easily be misinterpreted. Most people understood the message in a positive way, but there were two misconceptions. One misconception is that we make statements on virology. We only tested distance to the exposure of droplets. That’s aerodynamics; how do droplets behave in the airflow? I didn’t make any claims that infection rates would be higher or lower.
“And some people have said that I advised against going outside, running or cycling, which is the opposite of my intention. I am a keen cyclist myself. They should go out, but they should be careful. If you move too close to another person, stay out of their slipstream, but if you want to be in slipstream, keep a longer distance.”
While the research encouraged keeping fit “to ease one’s mind in times of Covid-19”, it advised exercising in a staggered formation to avoid the direct slipstream of others, and to ensure a wide berth when overtaking.
This advice on physical distancing to each other is really about reducing the risk of transmission rather than eliminating it altogether. This isn’t to say that you should stop exercising outdoors entirely, just be sure to keep a safe distance of 2m, and an even greater distance (and staggered) if you are a runner or cyclist choosing to do so outdoors.
The message is, keep on exercising, but stay out of slipstreams
- Professor Bert Blocken