That would likely require masking also.
I’m sorry that I am just a lowly engineer and not a scientist but: if you place a restriction into the flow of a fluid or gas it creates a restriction. That restriction creates a pressure difference and in order to maintain the same flow without the restriction, more power is needed So if I inhale a liter of air with each breath, my lungs have to work harder to supply that liter when a mask is over my face. Note, this additional power comes from the heart which is also affected. The numbers may be small or not, but there is an impact to the body.