Hi all, almost a year later and I am noticing the exact same thing 
Have just completed Ansel Adams -2 which is an anaerobic session, yet each interval pushed my heart rate to upper Z2 / lower Z3, with cardiac lag not of relevance as my total time above Z2 was 6 mins which fell into low Z3. Nothing in Z4 or Z5.
So in the knowledge that a polarised approach is considered appropriate, i’m curious as to whether I am getting the physiological adaptions desired from the anaerobic work as I am able to hit the goal wattage numbers, or should i discount the desired wattage numbers and push harder to hit the Z4/Z5 required of HIIT?
Appreciate your thoughts on this.
Thanks
lee