oxygen consumption4 There were no significant differences in peak oxygen consumption or peak workload with and without the nasal strips5 No difference between the strip and a piece of tape6 No difference in post-exercise recovery7 No difference for perceived exertion and perceived breathing effort during sprints8Right. So that's why we only saw athletes wearing them for a season. Plus, they looked stupid. The original hypoxic masks also looked stupid. The new ones make you look like Bane, sans Sean Connery voice. We've seen numerous athletes training in them already, but are they a fad like the nose tape? And what does the research say? The Problems With Most of the ResearchIt's important to note that there isn't a tremendous body of literature on hypoxic training. In addition, the vast majority of existing research was done by having subjects exercise in a room that simulated atmospheric hypoxia (translation: the air didn't have as much oxygen).Other tests had subjects strap a mask to their faces with a huge oxygen regulator attached by a tube to the other end (so they couldn't do much moving around). Those tests were typically limited to treadmill running or stationary cycling. The masks that we see being sold, well, if they work like training at altitude or in one of these special hypoxic rooms, then we can expect them to have the same effects.Looking over the available research, here are some of the more relevant studies I found: Hypoxic sprint interval training (thirty-second sprints with four minutes of rest, progressing from four to seven over six sessions) showed no advantage with simulated hypoxia. But this study (six sessions total) seems too short to draw any conclusions. A six-week study demonstrated that sprint interval training in hypoxia upregulated muscle phosphofructokinase activity and the anaerobic threshold more than sprint interval training in normoxia, but still did not enhance endurance exercise performance.9 I believe this was also probably too short. I'm not saying a performance benefit with simulated hypoxia is certain, but if it's showing improved adaptations over normoxia after six weeks, it's not a huge leap to believe it could happen. However, a different study showed that hypoxic conditions combined with sprint training has the ability to stimulate glycolyitic enzyme ability, which would obviously impart a training adaptation if the effect were high enough.10 Sprint training at hypoxia equivalent to 2,400m (five sets of three-minute work intervals) showed trends towards improving some areas. Rating of perceived exertion was higher and changes in bicarbonate levels and EPO trended towards possible improvement over normoxic conditions, but changes in 20m sprint time trended lower.11 And yet another interval training study, this time in cyclists, found no differences with hypoxic training, either by performance or measurement of monocarboxylate lactate transporter expression.12 In addition, fat oxidation was shown in one study to be slightly diminished (which can be a good thing, if we're looking for endurance and increased substrate efficiency), and had no additive effect on maximal measures of oxygen uptake (VO2peak) or time trial performance (measured under normoxia).13Obviously, the results of acute hypoxic exercise are