[Scott Johnston]

Joe:  Great questions.  Have you done an AnT test to see the spread between AeT and AnT?  With a 9:30 pace at AeT it is possible that this spread might be less than 10%, in which case you might want to be doing more of your aerobic base training down in Zone 1 or around 125-135.  That’s not far off your suggested 124 starting HR. Pacing on longer runs is always tricky.  Have you tried that strategy of starting in the 102s?  If so did you feel better at the end than if you start in Z2?

The bigger question is how do you feel the next day after longer runs done with these two strategies?  It sounds like you blow up if starting in Z2.  That in itself tells you the answer.  Z2 is unsustainable for you for more than 2 hours right now.  It will improve with time but the best route to accomplishing that is to do more easier volume.

I hope the helps,
Scott