Heart rate and power mismatch

Hi guys,

Quick question; I regularly do zone 2 endurance type work on my indoor trainer. Same setup, same cooling, etc. Most days my heart rate and power both nicely align in their appropriate zones but on some days my heart rate just tends to drift a bit higher than usual and barely drifts into zone 3. The effort doesn’t particularly feel any more intense than usual.

What would be the wise thing to do in such situations? Keep going, knowing that I’m hitting the correct power zone, or just take a rest day and wait for everything to align again?

Any help is much appreciated. Thanks in advance!

Unlike power, there isn’t an agreed upon standard for heart rate zones.

Example power zone2 endurance ride:

Better match between Coggan power zones and Friel HR zones.

I do (most) workouts by power and post-ride look at Friel HR zones.

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Ignore HR, its such a fickle thing.


Not sure this is helpful, but here is the TR blog and vid on the topic:

It’s not. But you kind of knew that. Power = Load, HR = Strain. Both are useful.

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I don’t see such agreement for power zones. Your estimates of Friel and Coggan could be both wrong.

Power and HR zones are estimates, don’t have to match, and I don’t look for precision.

Unless you know there’s a variable strongly influencing your HR like being sick, or extreme heat…HR at the aerobic threshold is very consistent and will probably be the same the rest of your life if you keep training…but if you keep improving the power will go up. Learn to triangulate between RPE, power and HR. If you want to do endurance during early base season, preferably go with HR mostly.


I probably should have noted that I’m using a 7-zone model for Heart rate (the one provided by intervals.icu) and today for example I was slightly drifting out of the Aerobic (Z2) into Tempo (Z3).

Regarding the Power vs Heart Rate graph; not sure what to make of that yet, part of my 2021 data was based on a wrist HR-monitor. I’ve measurably improved since then in my Z2 efforts, but I’m not sure I can see that in this graph…


EDIT: Forgot to say; thanks for all the insights guys. Much appreciated.

Holding out for a firmware update so I can do a heart spin-down calibration…

Well… I know that heart rates vary and drift. The question was whether I should ignore the drift and remain in the correct power zone, or tone down the power and ensure I’m in the correct heart rate zone…

Use power as your guide always unless you have got a diagnosed heart problem. Power is constant whereas HR is fickle and you want consistent training.