You've all seen those guys in the gym—the ones who look like Bane and sound like Darth Vader hopping from one exercise to the next. Maybe you've though to yourself, "what is that awesome looking gadget," or, if you're like me, something along the lines of "what exactly does this tool think he's accomplishing?"
Many Olympic marathoners utilize altitude training to take their fitness to the next level (pun intended), so it makes sense that these masks would be worth the money.
What these companies aren't telling you, however, is that the research doesn't support these absurd-looking masks. On the contrary.
The positive adaptations of altitude training include an increased red blood cell count. This is one such adaptation that will only come from prolonged exposure to higher altitudes (meaning wearing a mask for an hour a few times per week isn't going to help in that arena. I most often see people wearing these masks on exercise machines (like the bro in the photo). Even if these masks were to work, you certainly wouldn't want to wear them for an exercise that doesn't rely on oxygen for energy (anaerobic exercises).
Another huge flaw in the reasoning behind wearing these masks is that they do not result in a change in barometric (atmospheric) pressure, as we would find in mountainous regions. Instead, they merely restrict your respiratory muscles, which effectively make breathing more challenging. These two things are not the same. In fact, in my opinion, limiting the efficacy of the respiratory muscles is just dangerous and foolish.
Finally, the current theory for altitude training is the "live high, train low." This means that athletes should live in higher altitudes, but train in lower altitudes so as not to impede their physical performance (obviously we cannot perform maximally at 10,000 feet above sea level). The altitude training masks directly contradict this principle, as people are not wearing them to do their household chores, but rather to do biceps curls in the squat rack. You definitely don't need to be an exercise physiologist to understand why this won't confer any added athletic benefits.
If you want to improve your aerobic capacity, avoid the scams and gimmicks. You can't take a shortcut to attain peak fitness levels (without the use of PEDs, of course), so quit throwing your money down the drain and put in the hard work. These masks will make you the laughing stock of your gym and they certainly won't provide any physiological advantage in your training.