Originally Posted by RapDaddyo .
Alex's example illustrates one effort on one day at a constant HR, which illustrates the persistent decline in watts throughout the duration of the effort. If you used this protocol for, say, 3x20s with 5min rest durations, I would expect to see a difference in AP for each effort. And, if you did the same workout on two different days, I would expect to see different APs for each effort within each workout and for the same effort on different days. So, AP for Day1_Effort1 will not be equal to AP for Day2_Effort1, and so on. And, if you throw in a difference in cadence for the different efforts, the differences will be larger. For purposes of cycling training, HR provides one important fact: you're alive.