||How an altitude mask functions|
Many of the masks available on the market simply restrict your breathing so you can’t pull air into your lungs as fast as normal. When you exercise with one you basically get out of breath sooner, at a lower exercise intensity level, than normal. You’ll also accumulate more CO2 in your blood. But the composition of the air you’re breathing is the exact same as it was without the mask. You’re only getting less oxygen because you’re getting less air.
Exposure to true altitude is different. Here in Colorado Springs at 6200 feet above sea level, the percentage of oxygen in the air is the same as it is at sea level (about 21%). But since the air pressure is lower at altitude those oxygen molecules are further apart, so there are fewer of them in a lungful of air. You’re breathing in the same volume of air, there’s just fewer molecules of oxygen in it. Altitude tents and altitude rooms like the High Altitude Training Center at the US Olympic Training Center in Colorado Springs work in a similar way. They remove oxygen from the air you’re breathing so that when you draw in a full breath there’s simply less oxygen in that volume of air.
The point is, an altitude training mask is not simulating the same type of hypoxia athletes experience either living or training at higher elevations, and that seems to be a crucial difference.