|MadSci Network: Anatomy|
Breathing in through the nostrils and out through the mouth is healthier since the air has a chance to be filtered as well as warmed and moisturized. This is especially important in cold weather for people with asthma. However, when the demand for air increases at high levels of exercise there is too much resistance in nose breathing for adequate oxygen supply. In the case of extended running it is best to use mouth breathing. When running in cold weather it is best to wear a mask or scarf over the nose and mouth so the air can be somewhat properly warmed before getting to the lungs.
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