Apparently competitive athletes do this to improve their CO2. This cyclist who invented the tape said his CO2 went through the roof after a month of taping.
I find it practically impossible to keep it shut the entire time but am getting better at it and find that you get more focused (kind of like in yoga).
My ex-boyfriend was a competitive cyclist and he said he knew guys who used to tape their mouth and place straws in their nose when doing hill climbing workouts outdoors. I thought that was nuts but now I'm trying it so never say never right!
Here's more on
Buteyko Breathing if anybody wants to learn more. This method is great for asthma, sleep apnea, anxiety and other conditions.