I solved the mystery. After wandering aimlessly through Google I stumbled upon "elevation training mask." It is a mask that has varying levels of resistance to breathing to build your breathing muscles with varying levels of asphyxia. Sounds terrifying. The design is based on that of the Israeli gas mask, and comes from the University of Nait.

There is also an altitude training mask somewhere that actually removes some oxygen from the air you are breathing to simulate Denver.

I can see where EPO and auto transfusions would be more attractive than these masks.

entertaining nevertheless