Many gyms and health clubs appear to be filling up again with people eager to get back into their old routines and communities or get in shape for the summer, at the same time that new omicron variants are driving up COVID infections. So how safe is it to get back in the gym?
Put another way, how many microscopic aerosol particles are the other cyclists in your spin class exhaling into the room? How many is the runner throwing on the nearby treadmill? A small study on breathing and exercise published May 23 in the Proceedings of the National Academy of Sciences provides some surprising answers.
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The study looked at the amount of aerosol particles exhaled by 16 people at rest and during workouts. These tiny airborne bits of matter, measuring just a few hundred micrometers in diameter, or about the width of a strand of hair, and suspended in the mist of our lungs, can transmit the coronavirus if someone is infected, carrying the viruses through the air. from one pair of lungs to another.
The study found that, at rest, men and women exhaled around 500 particles per minute. But when they exercised, that total jumped 132-fold, topping 76,000 bpm, on average, during the most strenuous exercise.
These findings help explain why there have been several notable COVID superspreading events since 2020 in indoor gym classes. They could also renew some people’s concerns about indoor gym programs as COVID-19 cases rise again across much of the nation and raise questions about how best to reduce exposure risks when we exercise.
In general, packing gasping bodies indoors is a poor way to prevent transmission of COVID-19 or other respiratory illnesses. In 2020, 54 South Koreans developed COVID after Zumba classes with infected instructors and then passed it on to family and acquaintances. Later that year, all 10 members of a spin class in Hawaii taught by an infected instructor later tested positive, as did 11 others who came into close contact with one of the class members, a personal trainer and kickboxing instructor. .
Scientists investigating these and similar outbreaks speculated that inadequate ventilation and high breathing rates among athletes contributed to the spread of COVID-19 in affected gyms. But the scientists could only guess to what extent exercise had increased the levels of aerosol particles in gym areas. It is difficult to accurately measure the increase in buoyant particles during exercise.
So for the new study, a group of exercise scientists and fluid dynamics researchers in Germany came up with a novel way to measure aerosol emission, using a single stationary bike and a cyclist inside an airtight tent. The cyclists wore silicone masks that captured their exhaled breaths and sent the air through tubes to a machine that counted every particle in its path.
The researchers first measured people’s particle production while they were sitting and then while they rode at an increasingly demanding pace until they were too exhausted to continue. The particles were constantly counted.
The scientists expected that athletes’ aerosol production would increase as intensity increased. We all breathe deeper and faster as we exercise more. But the extent of the 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 off modestly as cyclists warmed up and started pedaling harder. But as they reached a threshold where their exercise became noticeably more strenuous—about the time jogging turns into a run or a spin class switches to intervals—the increase in emissions became exponential. The cyclists began inhaling about 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 (with considerable variation from person to person).
In a room full of spin cyclists, treadmill runners or campers, “the concentration of aerosol particles would increase a lot,” said Benedikt Mutsch, a graduate student at the Institute for Fluid Mechanics and Aerodynamics at the University of the German Armed Forces. . in Munich and co-author of the study. The more particles, the more possibility of infection by COVID-19 if an athlete is infected.
“The study provides mechanistic data to support the assumption that indoor exercise is a higher risk activity when it comes to transmission of COVID-19” than outdoor exercise, said Linsey Marr, a professor of civil engineering. and environmental at Virginia Tech. and an expert in airborne transmission of viruses.
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 your gym windows are closed, ask the manager to open them wide and turn up the volume on the fans. If the weather is sweltering and air conditioning is needed, make sure your gym units draw air from outside so that fresh supplies replace air filled with aerosol emissions from you and your classmates.
You can also suggest that the gym install room air filters in each workout area, Cappa said. “These can be really effective in reducing the risk of transmission by removing the virus from the air.” They can be purchased commercially or even made at home, he said.
Also, stay away from other athletes. “Social distancing of 6 feet or more is always important,” Mutsch said. But it may not be enough during strenuous indoor exercise classes. The new study didn’t track where the aerosol particles from the cyclists flowed, but they likely flowed well beyond 6 feet, he said. Therefore, maintain a distance of at least 8 to 10 feet during strenuous workouts, which require large rooms and small class sizes.
The classes themselves should also be well spaced. “If there are back-to-back exercise classes, some of the air from that first class will carry over into the second,” Cappa said. Make sure there are breaks of at least 15 and preferably 30 minutes between sessions to allow the air to clear.
Mask too. “Respiratory face masks reduce aerosol emissions,” Wackerhage said.
If you find a tight N95 mask uncomfortable during intense exercise, “I suggest wearing a good surgical mask,” Cappa said, which may feel a little less tight and filmy.
Finally, check the incidence of COVID-19 in your area. “The higher the local case rates,” Cappa said, “the more likely it is that an infectious person will be in the class with you.” If rates are rising, perhaps bike, jog, walk, or stroll outside until cases decline.
But keep moving. This study “is more of an incentive to ensure great ventilation and no crowding in gyms,” Marr said. But it’s not a reason to skip workouts. “Exercise has so many benefits,” she said, “that I will continue to do it in my well-ventilated, non-crowded gym.”
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