Wearing a mask DEFINITELY decreases the total oxygen going into your lungs! I bought one of those blood oxygen sensors and tested the with and without blood oxygen, and it IS a few percent lower with the mask on. The question is, what is the long-term health effect of a few percent less oxygen? Perhaps it's the same as living at higher elevation, and will not be a factor (and could arguably help those people if they decide to enter a race without a mask, at sea level :) ).
Higher elevation doesn't concentrate the CO2 around your face, though. The mask does that and I suspect that's where the loss in O2 percentage is coming from.
Wearing a mask DEFINITELY decreases the total oxygen going into your lungs! I bought one of those blood oxygen sensors and tested the with and without blood oxygen, and it IS a few percent lower with the mask on. The question is, what is the long-term health effect of a few percent less oxygen? Perhaps it's the same as living at higher elevation, and will not be a factor (and could arguably help those people if they decide to enter a race without a mask, at sea level :) ).
Higher elevation doesn't concentrate the CO2 around your face, though. The mask does that and I suspect that's where the loss in O2 percentage is coming from.