You might want to start your next workout at the gym with a sniff test. A new study suggests that gyms have high levels of air pollutants such as formaldehyde, airborne dust, and carbon dioxide, reports the New York Times.

In fact, levels for those three substances generally exceeded accepted standards for air quality. The samples were taken at gyms in Portugal, but the gyms were similar to those commonly found in the US.

Researchers found particularly high levels of carbon dioxide during aerobics classes, thanks to all that huffing and puffing. But the need for better ventilation seemed clear in all areas, especially considering the physiology involved with a workout.

"When we exercise, we take in more air with each breath and most of that air goes through the mouth, bypassing the natural filtration system" of the nostrils, says the lead researcher.

"The pollutants go deeper into the lungs compared to resting situations." So what to do? The researchers stress that people shouldn't stop going to gyms, notes a blog post at Shape.

But they might want to sniff their gym's air, and if it has a stale or chemical odor, ask the manager about ventilation or the most recent air-quality test.

Beyond that, exercisers could make a point to go at less-crowded times, suggests Men's Fitness. (Exercise might be bad for your teeth, too.)

This article originally appeared on Newser: Air Quality in Your Gym Might Spoil Workout

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