Over all, the study offers both cautions and guidance for anyone considering an in-person return to dance, yoga, boot-camp or similar group exercise classes, both the authors and other experts agree. “Exercising in a gym will make you vulnerable to infectious disease,” Dr. Rhee says. But limiting class sizes and sticking with low-intensity exercise, which entails little heavy respiration, might help to lessen viral transmission.

Proper air circulation also is essential, says Linsey Marr, a professor of civil and environmental engineering at Virginia Tech University, who studies airflow. She was not involved with the South Korean study but read it at my request. “I have actually thought about this issue a lot,” she says, “because I’m an avid CrossFitter and I want to get back to my routine. But I think indoor exercise classes can be conducted safely only if there is sufficient ventilation with outdoor air, not recirculated air.”

To reduce infection risks from airborne virus particles, she says, the current recommendation for airflow calls for about 10 liters of outdoor air per second, per person in the room. In practice, the more people in an exercise class, the more outside air needs to be flowing in and out. If you are returning to the gym or workout studio, ask your facility’s manager about their ventilation system. If the air-conditioning system does not draw in air from outside, request that the staff open all available windows and doors.

Social distancing remains necessary, too, which means class sizes almost certainly will need to be smaller than they might have been in the past. “Relatively large numbers of participants, all breathing heavily in a small space, provides ideal conditions for viral spread,” says Alexandro Andrade, a professor of exercise science at the State University of Santa Catarina in Brazil, who studies the effects of air quality on health and physical performance.

Masks or other facial coverings are likely to be required during classes, depending on local regulations or facility rules, and should be encouraged everywhere, Dr. Andrade says.

Moving group classes outside, too, if possible and practical, could bolster natural air flow, widen interpersonal spacing and drench the class in sunlight, he says. But avoid outdoor classes if they are conducted between high walls or buildings, since those bulwarks prevent the breeze from dispersing people’s expired breaths.


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