Perhaps short training in low oxygen stimulates erythropoiesis (red blood cell creation) which in tern allows more hgb to be available to allow for more oxygen to be attached thus making each breath more efficient.
The question is how much oxygen deprivation leads to a body system change.
My bet is that snorkels don't work and that's why Lance doped for the tour. If all it took was snorkel, I bet he'd have done it.
