@Scott Semple – no, you are right, it is HR zones. By “running” zones – I meant the 7 Friel HR zones for running on Training Peaks (the auto set).
It’s funny, I usually jack up the pace on the first interval intentionally to get my HR into the zone as quickly as possible during that first interval (I figured that was better???). But yeah, it gets there much more quickly on latter ones.
So maybe keep the pace at a consistent level to get the HR into the zone by the middle to end of 4 min interval on the first one and see what happens if I keep it there for the rest without creeping in to Z5.
Super helpful, thanks!