Why the Air at the Gym May Be More Likely to Spread Covid

Many gyms and health clubs seem to be filling up again with people eager to return to their old routines and communities or get in shape for summer, at the same time that new Omicron variants are pushing Covid infections up. So, how safe is it to go back to the gym?

Put another way, how many microscopic aerosol particles are the other cyclists in your spin class breathing out into the room? How many is the runner on the nearby treadmill spewing forth? A small study about respiration and exercise published Monday in the Proceedings of the National Academy of Sciences provides some rather startling answers.

The study looked at the number of aerosol particles 16 people exhaled at rest and during workouts. These tiny bits of airborne matter — measuring barely a few hundred micrometers in diameter, or about the width of a strand of hair, and suspended in mist from our lungs — can transmit coronavirus if someone is infected, ferrying the virus lightly through the air from one pair of lungs to another.

The study found that, at rest, the men and women breathed out about 500 particles per minute. But when they exercised, that total soared 132-fold, topping out above 76,000 particles per minute, on average, during the most strenuous exertion.