This is resistance mask training. There is evidence that shows when you wear the mask, it restricts breathing and tasks the lungs. When combining this with specific exercises programming, it can cause an increase in your VO2 max, which means you are literally improving your respiratory performance. Lots of professional athletes have used this and stand behind it. It is currently being tested in professional teams and there is lots of new scientific date that is coming out showing the improvement of Lung and Resistance Mask Training.