You act like you are the first person to discover this. I think many of us have observed this and tested it. It's pretty well known that HR is very much affected by fatigue, as well as sleep, stress, caffeine, etc. This is why training with power is more effective than training with heart rate.
Yeah, it's all old news. But, from the kinds of comments I see - i doubt many people actually check their own stats as intimately as I have.
This is why training with power is more effective than training with heart rate.
This is the kind of silly crap that passes for knowledge. Actually, training with all the types of biofeedback available is the best methodology. Using "power" as a single measure of applied training stress does not preclude the benefits of other information.