There really aren't any physiological restrictions to breathing with a mask on. Sure, there are some psychological reasons (anxiety, claustrophobia, etc) that can manifest as a physiological response, but there isn't a valid direct relationship. I worked as a PT in a hospital a couple years ago, seeing patients daily with very, very severe lung disease. I'm talking days away from dying or lung transplants bad. Walking 50 feet down the hallway would put similar stress on their lungs as a healthy person running a marathon. Guess, what, these people would regularly wear masks with all activity with no change in their oxygen levels, since they were so sick that any kind of illness could be fatal. The inhalation of CO2 is soooo minute that it should not alter one's blood chemistry, especially in someone who is healthy. Medical professionals wouldn't purposely try to restrict someone's breathing further when it is already so severely compromised. Is it uncomfortable, sure. Does it take getting used to, absolutely.
This is primarily in regards to surgical or cloth masks. N95s are a bit different, but I really hope nobody is wearing one of those to a cheer practice.
Not trying to minimize anybody's experiences, just sharing my thoughts and what I've learned in the medical field.
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