The o2 Trainer

No personal experience. But a weak diaphragm is not why anyone is out of shape. Gimmick. Even if you are at sea level just get out there and get in shape. A week before my first mountain hunt I ran a 2:36 marathon at 400ft altitude. Lived at 600ft altitude. Hunted at 6000-8500ft altitude, kept up with the local guys easily.
 
It's very similar to training mask.
Or that's what one was called for a bit.
Seems a lot of guys were using them well before they were being marketed. Several guys use them and swear by them. Bas gets behind some hood products so definitely worth a try.
 
Gimmick.

There's a reason why people "live high, train low"....and that ain't it.
 
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