Purchased on Amazon and never used. This is a running training mask. 【6 Levels of Adjustable Breathing Resistance】 This training mask has a total of 6 different breathing resistance levels, which can simulate breathing environments at different altitudes. Users can adjust from the lowest intensity level 1 to the highest intensity level 6 according to their endurance. And, when the resistance level is adjusted, the user does not need to remove the mask, which is very convenient. If you can adapt to higher intensities, your physical strength, resilience, and endurance will be further enhanced. Type...Mask/Face Cover Features and Shape...Unisex