Thought I would ask on here as there seems to be split opinions on whether mask like the one in the vid work. Initially I thought there would be some heightened oxygen levels being absorbed. Apparently though that is not the case. Jerome Pena is on a reduced supply. Some of you may have seen to content already, but surely deliberately training on a reduced oxygen supply would be quite dangerous. This guy is obviously uber fit, but would anybody be risking a black out by training in this way, even if you handle the intensity. More to the point, does it actually work? Any members on here done this, or something similar.