Dolphy Fitness Mask for Fitness/Training (Medium) Dolphy Fitness Mask contains adjustable resistance valves allowing you to control the altitude resistance level to suit your progress from 3000 ft. to 18000 ft. The mask restricts breathing which makes people feel like they are at high altitude. It basically gets people out of breathing which makes people feel like they are at a high altitude. It basically gets people out of breath sooner than normal. However, the composition of air remains the same as it is when you breathe without the mask. It helps condition the lungs and strengthen the diaphragm, thereby increasing the overall lung capacity and improving oxygen intake. It also claims to increase mental focus and decrease workout time. For the same reason, it is used by athletes during fitness training. The high-altitude mask or elevation mask not only makes the workout efficient, but also conditions the lungs and makes them work harder. When lungs work harder, the stamina and energy levels improve.Meet the Dolphy High Altitude Training Mask and Unleash a Better You Competitive athletes have long sought after altitude exposure to gain an edge on their competition, and for good reason and now you can too. You will instantly begin to notice the difference and perform better in your workouts, aerobic activity, or all other physical endeavors. Even if it's just to crush your one mile time every week in the gym. Otherwise know as the practice of limiting oxygen availability while training, and has been used for decades to improving optimal performance. Training in this type of high altitude environment will boost the production of red blood cells and aid stamina. Benefits: “ Improves your stamina lung capaicty “ Experience Better Workouts “ Less fatigue during High-Intensity Workouts Risk.