This is also something I prescribe heavily to. Watch the trend in your HR with the power your putting out over time during intervals. A high sweet spot and threshold effort interval that is 5, 10, 15min long will definitely find a leveling point. It’s an aerobic effort, so your aerobic system should get into a fairly decent steady state.
If your HR is constantly creeping up during steady state efforts, then it’s usually a good indication that your FTP is set too high and you should dial back the power to find the steady state needed to develop that physiological system.
Of course, there will be decoupling, we all fatigue. But watching this trend during workouts with medium length interval work is a good way of knowing you’ve got power, HR, and RPE aligned.
Edit: just as an example. This is my last interval from this morning’s workout Abbey. You can see that even at the end of the workout when I’m most fatigued, my HR achieved a steady state (I added a straight dotted line to help illustrate) and remained level. This is a good indication that my FTP and the workload prescribed in the workout are aligned with objective of improving my aerobic capability.
