A good while back I looked at restrictors for training and my recollection is they didn't show any benefit in studies. Unclear why. They're a lot tougher than a

A good while back I looked at restrictors for training and my recollection is they didn't show any benefit in studies. Unclear why. They're a lot tougher than any respirator I've tried so I wouldn't expect the respirator to have any benefit that direction. Altitude tents apparently do work but are more trouble and risk than I'm comfortable with.