Do altitude masks work?
Is altitude mask an effective tool to help athletes better adapt and respond to the demands of training and competing at high altitude?
The short answer is no.
Most masks just limit air supply to the mouth and nose, making it harder to breathe. That may help build diaphragm and lung strength, but it does not simulate altitude (i.e., it is not the same as true hypoxic training). Furthermore, a good rate of VO2 Max does not depend on lung capacity. Instead, VO2 capacity is a function of how efficiently the body uses oxygen and converts it into energy.
Training at altitude will, overtime, increase red blood cells. This means that the blood will be able to transport more oxygen to the muscles. However, increased lung capacity from masks alone will not provide the same benefit.
By training at altitude, the body adapts to lower oxygen content. That means that the body starts producing more oxygen-carrying red blood cells and hemoglobin. Through this change/adaptation, athletes experience better performance when returning to train and compete at lower altitude.
In conclusion, instead of using altitude masks, chose effective tools such as altitude tents and chambers. Note that it takes several weeks of continuous exposure to create physiological adaptations. Lastly, the body loses this adaptation fairly quickly absent exposure.