That gym member panting next to you in spin class may be exhaling a huge amount of aerosol particles — the kind that can transmit viruses, including the one that causes COVID-19 — leading to a “super emission” during intense exercise, a new study has found.
A person’s aerosol particle emission increased 132-fold on average when he or she worked out at the highest intensity — skyrocketing from about 580 particles per minute at rest to about 76,000 during maximum exertion.
That startling rise might partly explain “superspreader events” during high-intensity group exercise indoors, the authors wrote in Proceedings of the National Academy of Sciences.
In 2020, researchers in South Korea found 112 COVID-19 cases linked to fitness dance classes at 12 different gyms. That same year, Hawaii reported a “COVID-19 cluster” where 21 cases at three fitness facilities were linked to an instructor who taught a spin class and other group classes days before experiencing symptoms.
“Vigorous exercise puts out a lot of particles in the air and very small droplets that waft in the air, making it more likely that they’re going to linger around and you could pick it up,” Dr. Marissa Levine, director of the Center for Leadership in Public Health Practice at the University of South Florida in Tampa, told TODAY. She was not involved in the new study.
“It’s particularly worrisome as we see these waves of disease… if you have a variant that’s easy to transmit and you have a lot of them in a small space because people are exercising vigorously, that means your risk is going to be higher if you go into that setting.”
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Exhaled particles hang in the air
The findings have “important implications” for infection control during high-intensity gym classes such as spinning, P.E. classes in school, dancing during weddings and any other events where people are active together indoors, the study authors noted.
An experiment measured the exhaled air of 16 healthy young participants — eight men and eight women — as they worked out increasingly hard on a stationary bike. Each participant inhaled clean air through a face mask that covered their mouth and nose, while their exhaled air was directed into a “particle counter” to measure how many aerosol particles they were emitting.
As they went from rest to exhaustion, the researchers saw the huge increase of aerosol particles. The paper cited previous studies that found people who were positive for COVID-19 and exercised would “blow out” more of the virus into a room, while healthy exercisers would inhale more virus-contaminated aerosol particles than when at rest.
Just imagine all those exhaled particles hanging in the air — it emphasizes why good ventilation in indoor settings is important, Levine said.
“If you could see it, it would be obvious. But the problem is you can’t see it, so you just have to appreciate the science behind it, that good ventilation means we can move those particles out quickly and decrease your chance of being exposed,” she noted.
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How to stay safe at the gym:
It comes down to taking inventory of your own risks, asking questions about how the facility is keeping members safe and being aware of your surroundings.
Start by knowing your individual risk for COVID-19: Older adults and those who have significant underlying health issues are at higher risk. “I would really caution older folks who fit that bill to be really careful about finding themselves in rooms with younger people who are vigorously exercising, particularly in that small space,” Levine advised.
Ask your gym about what it has done about enhancing the ventilation: If you sense the air is stuffy, it can be an indication that the ventilation is not great, she noted. A recent report found only about one-third of schools replaced or upgraded their HVAC systems. Gyms are probably much less likely to do so than schools, “and yet they’re also places where those particles are produced,” Levine said.
“One thing that concerns me is that many facilities are emphasizing how they’re cleaning, which is OK. But this is a respiratory infection and spreads by respiratory means in the air, particularly by those small aerosols. So what’s even more important is what’s happening with the ventilation,” she noted. Room air purifiers with HEPA filters could help.
Be aware of the space you’re in: As a very general rule, a bigger space is potentially safer than a small room, but it also depends on how many people are in the room and what kind of exercise is going on inside, Levine said. If one group class ends, wait before entering the room for the next one so there is time for the air to be replaced — more than five minutes, but the longer the better, she advised. The study authors advised 15-minunte "airing breaks."
The 6-feet rule doesn’t work too well indoors: “These really small particles waft in the air and they could go anywhere in that room, depending upon the air circulation. Particularly if the ventilation isn’t very good, they could stick around for quite some time,” Levine said. If someone is vigorously exercising nearby, she advised people at high risk for COVID-19 to leave the room.
Carry a mask: An N-95 or KN-95 is better than a surgical mask — use it when needed.