[Newt]

Regarding snorkel and mask training, does anyone have any links to any studies showing that restricting/reducing the flow of low-altitude air (i.e., snorkel/mask training) is equivalent or comparable to actually breathing in air with a lower oxygen content (i.e., living/training at altitude)? To me, it seems that snorkel/mask training would merely develop the efficiency of the inhalation/exhalation muscles (and probably lactic acid tolerance), while breathing in air with a lower oxygen content would seem more likely to bring about the physiological changes traditionally associated with living at altitude (increased mitochondial density, red blood cell count, etc.).

Thoughts?