Hidden danger at the gym: How bodily emissions during sweaty workouts can create harmful chemicals

BOULDER, Colo. — Health experts usually worry about the emissions coming out of machines like cars, but it turns out emissions are also pouring out of humans too. Researchers from the University of Colorado-Boulder say one sweaty workout produces as many bodily chemicals as five people sitting still. Their study finds that for people in gyms these chemicals are mixing with cleaning products and could pose a danger to human health.

“Humans are a large source of indoor emissions,” says lead author Zachary Finewax in a university release. “And chemicals in indoor air, whether from our bodies or cleaning products, don’t just disappear, they linger and travel around spaces like gyms, reacting with other chemicals.”

Researchers say these human emissions include amino acids in sweat and acetone in a person’s breath. The study finds these byproducts combine with bleach and other cleaning solutions to form new airborne particles. It’s not yet known what impact these new compounds will have on air quality.

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Study authors set up air sampling equipment in the CU Boulder weight room back in 2018. The instruments collected data on both the campus facility and its air supply; measuring airborne chemicals before, during, and after the athletes worked out. On average, students working out produced between three and five times the emissions they did when at rest.

“Using our state-of-the-art equipment, this was the first time indoor air analysis in a gym was done with this high level of sophistication. We were able to capture emissions in real time to see exactly how many chemicals the athletes were emitting, and at what rate,” explains co-author Demetrios Pagonis.

The results find campus workers frequently use chlorine bleach-based products to sanitize gym equipment. These bacteria-killing chemicals mixed with amino acids in sweat to form a chemical group called N-chloraldimines. Researchers say the chlorine from the bleach reacted with amino acids in the gym air to form this new chemical.

Study authors say they need to do more research to see what impact chemicals like these have on people breathing them in. They caution however, that similar reactions between ammonia and bleach can be hazardous to human health.

“Since people spend about 90 percent of our time indoors, it’s critical we understand how chemicals behave in the spaces we occupy,” adds CU Boulder professor of chemistry and corresponding author Joost de Gouw.

Although the results come from gym samples taken prior to COVID-19, the team believes exercise facilities which have low occupancy and good ventilation will be relatively safe for working out. That’s especially the case for gyms that now require members to wear masks during their owrkouts.

The study appears in the journal Indoor Air.

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