[Scott Johnston]

Great questions. Thanks for asking.  Nose breathing is not a surefire method for everyone to establish their aerobic threshold.  Some people struggle to breathe through their nose, even at rest, due to congestion and swollen nasal tissue in the nose.  It sounds like when you redid the test starting at 135; you got a more reasonable drift.  I’d stick with that as the top of Z2 till you see some improvement in pace at that HR.  Your HR is the result of the tug-of-war between your sympathetic (fight or flight) and parasympathetic (rest and digest) nervous systems.  In your game, your excitement causes your sympathetic nervous system to overpower the parasympathetic.  Your brain can’t tell the difference between VR and reality, so is preparing you for a fight or flight.  When exercising, your sympathetic system jacks up HR in response to increased oxygen demand in the working muscles.

1. Cold will affect your ability to nose breathe 40F is probably not cold enough to have much, if any, effect.
2. Temps would need to be to the point of making your mucus membranes sting or burn to have much effect.  Forget nose breathing.
3. Go with 135 for now.
4. See the above explanation.

I hope this helps.

Scott