I’ve listened to podcasts on this, including the TR podcast and several others. I’ve not found a direct answer to my question. It seems that in a lab, or outdoors that a proper VO2 workout has your heart rate at 90-95% of max and power usually starts above threshold but by the last block may have moved down a bit to threshold or just under if the intervals are longer in duration.
But I’ve not seen much addressing less than ideal conditions indoors. Specifically what I’m getting on about is things like ventilation, body temperature, hydration, etc.
I’ve included screen captures of 3 workouts. Two of which were indoors, one of which was outdoors.
One indoor workout I did based on HR and basically got my HR to 185BPM which is about 95% of HR max and held it there decreasing the power.
A second indoor workout was done this week where I adjusted the power on the first two intervals to be a bit higher at the beginning but was still less power than my outdoor workout. The HR reached 192bpm where it basically sat there for several minutes in the workout. This is 98% of max HR. Yes it was hard, my legs hurt, I was breathing heavily but I was NOT about to die despite my HR being super high.
The outdoor workout is 4x5min with a couple of add’l shorter intervals at the end as the road allowed. Power was generally higher than the indoor workout, HR more controlled, but breathing harder at the end of the 4th interval. Legs were pretty tired at the end of the workout.
So this brings up a few questions. When I’m doing these indoors should be focused on power or HR? Some data suggest that HR above 96 or 97% of HR max for more than just a few seconds is COUNTER productive? In otherwords it pushes the heart and neuro systems too hard and blunts adaptation responses?
I am going to buy a proper fan at the end of this month for my indoor riding area, so I hope that helps with some of these HR drift that I have indoors, but I still need to know how to do a proper workout indoors to maximize adaptations.

Power vs Heart Rate: How Modern Athletes Train
The methods cyclists use to get faster have evolved over the years. Follow our discussion into why modern athletes train using a power-measuring device, instead of solely using a traditional heart rate monitor.