Altitude affects air density, not oxygen percentage. Training in thinner air helps boost red blood cell production and endurance. Problem with those masks is they don't work and they look stupid. Altitude is not bad if you allow yourself to acclimate to it. Wifey and I were fine in Peru. I was more gassed running around Europe last month than I was hiking all up and down Machu Picchu.
10/24/16 at 4:48am