The researchers first measured the subjects’ particle output while they sat still and then while they pedaled at an increasingly demanding pace until eventually they were too exhausted to continue. The particles were being counted all the time.
The scientists expected that athletes’ aerosol production would increase as intensity increased. We all breathe deeper and faster when we intensify the exercise. But the rate of increase “surprised us,” said Henning Wackerhage, a professor of exercise biology at the Technical University of Munich and lead author of the new study.
The increase in aerosol emissions started out modest as cyclists warmed up and began to pedal harder. But when they reached a threshold where exercise became noticeably more strenuous—regarding the time a jog turns into a run or running class spinning changes at intervals—the increase in emissions was exponential. The cyclists began to expel regarding 10 times more air per minute than at rest, while the number of particles per minute increased more than 100-fold as the cyclists approached exhaustion (which varied considerably from person to person). .
In a room full of cyclists from spinningrunners on treadmills or practitioners of endurance sports, “the concentration of aerosol particles will increase a lot,” says Benedikt Mutsch, a graduate student at the Institute for Fluid Mechanics and Aerodynamics at the German Armed Forces University in Munich and co-author of the study. The greater the number of particles, the greater the possibility of contagion of COVID-19 if any of the exercisers is infected.
“The study provides mechanistic data that supports the hypothesis that exercising indoors is a higher risk activity for COVID-19 transmission” than exercising outdoors, said Linsey Marr, a professor of civil engineering. and environmental at Virginia Tech and an expert in airborne virus transmission.
But these risks can be mitigated. “Good ventilation and air exchange is a great way to reduce the risk of transmission,” said Chris Cappa, a professor of civil and environmental engineering at the University of California, Davis, and an expert in airflow dynamics.
“Open windows, especially with fans, can often be just as effective as active ventilation systems,” he said. If the windows of your gym are closed, ask the administrator to open them wide and turn the fans on full blast. If the weather is oppressive and air conditioning is required, make sure equipment draws air from outside so that a fresh supply replaces the aerosol-laden air you and your teammates exhale.