Looks like Polar is using the Karvonen zones also referenced in the Stryd description I posted. And I’ve never “liked” that zone breakdown, for me it just never tracked closely to my training or how it “felt”. Similar to what you wrote.
The Training Peaks guys know their
and I’ve always liked their analysis.
But at the end of the day, your zones should reflect how your body feels and responds in each training zone, and your best bet is to dial that in for you as closely as possible.
But for me, other than some minor drift in anaerobic threshold HR due to fitness or altitude, the TP formulas have been spot on for me, personally.
Now, that said, I have to say that i prefer to train to power, while monitoring HR (instead of training directly to HR), because HR can also sometimes be finicky, and also lags effort by 30-60 seconds.
But most importantly learn what each of your zones “feels” like so you don’t have to keep looking at your device constantly;)