[Scott Johnston]

There is no formula for zone adjustments when moving altitudes. However there will be a significant difference in AeT at these three elevations.  The approach we use in cases like this is to test at the different altitudes.  If that is too much hassle, based on my observations I would reduce AeT HR 5-10bpm from your 8000′ testing altitude when at 10k and raise it by 15-20 when training at 4k.

Scott