Computational Fluid Dynamics simulation done as part of ANYSYS’s COVID-19 Simulation Efforts:
“Leave additional space when exercising
Standard social distancing guidelines are insufficient when exercising outside. Analysis by Ansys partners Bert Blocken and Fabio Malizia at TUe & KU Leuven has revealed that substantially more space is required to avoid droplets from the runner or cyclist in front of you.“
Click on this video to see how respiratory droplets travel when running.
Note that while running side-by-side is best for avoiding runner-to-runner transfer, remember to be respectful of the more important need of others on path to avoid you. Forget about pace and move to the side to pause to allow others with good social distance.
Here is the academic paper associated with the simulation.