Outdoor training with COVID-19

Jérémie Chase, Physiologist and Strength & Conditioning Coach

Spring is here! As the weather warms up, many athletes are now looking to take their training to the great outdoors. This is especially true of athletes in endurance sports, who typically train and compete outside, and curse the winter months of indoor training.

With the COVID-19 pandemic happening, there is a greater interest from both athletes and the general public about how germs and viruses spread. Recently, articles have circulated on social media discussing how the current “social distancing” guidelines might not be adequate when doing physical activity.

Right now, most North American governments are recommending individuals to stay a minimum of 2 metres (6 ft.) away from one another to reduce the risk of spreading the virus. These distances were based off a study from the 1930’s showing how droplets spread around a standing adult.1 These guidelines have been scrutinized lately, with some evidence showing that smaller viruses (such as SARS and COVID-19) can be trapped in aerosol particles, which are even smaller water droplets and can stay suspended in the air for longer periods of time.2

Even assuming the guidelines are still acceptable, we must note some distinct differences when comparing standing and being physically active:

  • Level of exertion – Standing does not require a lot from the body. When active, especially at higher intensities, active individuals breathe in a lot more air, and exhale a lot more forcefully, sending their breath a lot further than when sitting.
  • Movement – When inactive, droplets from the mouth are exhaled in front of the body. Barring any wind, they will likely fall in the area in front of the breather. When active and moving, the exhaled breath will hover in the air, but the active individual’s forward motion means that those suspended particles are behind them near the point of exhalation until they make their way to the ground. Anyone following closely behind the active individual could unknowingly get a face full of aerosol particles from their breath.

A recent aerodynamics study examined this concept of how aerosol particles moved about around active individuals using wind tunnel simulations3. Essentially, there is a “comet trail” that gets formed behind an active individual, which is longer the faster they are moving. It can probably be assumed that this trail is also denser the harder the individual is exercising. The authors noted that being behind at a diagonal from the individual reduced the exposure to droplets.

In the end, the authors of the study recommended the following distance behind someone:


Activity Distance Approximate visual example of distance
Brisk walking (4 km/h) 4-5 metres A typical sedan car (4.5 m)
Running, slow biking (14.4 km/h) 10 metres A typical full-length school bus (13 m)
Fast biking (30 km/h) 20 metres A full-sized semi-trailer (21-24 m)

Note – they did not account for any crosswind in this study.


The purpose of this article is not to discourage being active outdoors. It is to make sure that it is being done so safely for the health of everyone around.

The take-home points for those itching to get outside are these:
  • Be aware when passing others while walking, running, or biking. The faster you go, the more time you should take before cutting back into the same “lane” as another individual.
  • If you are getting passed by a faster walker, runner, or cyclist, keep an eye where they cut back in front of you. If you think it is too close, try to bypass their “comet trail” or pause to give it time to settle.
  • Keep in mind the direction of the wind and take a cautious guess as to how that might impact aerosol particles from those near you.
  • If the location where you are exercising does not allow you to follow the above recommendations, it is likely too busy, and an alternative location should be considered.
  • From those exercising in groups, give more space, even as social distancing guidelines get eased. Experienced cyclists and runners that train while drafting off one another should avoid doing so during the COVID-19 pandemic. This should also be considered in a post-COVID future where the health status of lead riders and runners should be considered to reduce the risk of spreading any illness to a whole group/team.

Stay safe and healthy!


References

  1. Wells, W.F. On air-borne infection: Study II. Droplets and droplet nuclei., American Journal of Epidemiology, Volume 20, Issue 3, November 1934, Pages 611–618, https://doi.org/10.1093/oxfordjournals.aje.a118097
  2. Bourouiba L. Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19. Published online March 26, 2020. doi:10.1001/jama.2020.4756
  3. Blocken, B., Malizia, F., van Druenen, T., Marchal. T. Towards aerodynamically equivalent COVID19 1.5 m social distancing for walking and running. Article not yet peer-reviewed.