You may visit a gym because you are concerned about your health, but have you ever thought about the fact that the air you breathe into your lungs while exercising may contain harmful contaminants? A recent study from the University of Lisbon in Portugal and the Technical University of Delft in the Netherlands discovered this to be the case. They tested the air-quality by placing monitors in the weight room of 11 gyms, as well as several other areas of the gym such as the exercise and yoga studios. These monitors measure carbon monoxide levels, carbon dioxide levels, dust particles, and chemicals like formaldehyde (CH2O). According to their findings, these gyms tested high in amounts of airborne dust, formaldehyde, and carbon dioxide. These pollutants are dangerous to your health; they can lead to asthma and various other respiratory problems.