Someone here gave a great idea a while back. If you have or have access to a high-altitude (elevation) training mask, just remove the filters from it.

As an added benefit, it makes you look more badass than the typical lame mask. The effect is somewhat lessened if you look like someone who's never seen the inside of a gym (in other words, like me).

Someone here gave a great idea a while back. If you have or have access to a high-altitude (elevation) training mask, just remove the filters from it.