Difference in heart rate for few watts in Z2

Hello there,

I find that in my Z2 rides, I can ride at 210 watts at 120 BPM, give or take 5 BPM depending on the day.

But if I up it to 220, which seems to be a very small difference, my pulse goes up to 135 or so.

What is the explanation here? Would it make sense that I try to target the 220 watts and try to become more efficient there?



Seems to be a switch point for demands (muscular/metabolic) of the body when you move up 10 watts. Have you trained exclusively at or below 210 watts for an extended time?

I do most of my z2 training at 200ish watts. It usually keeps my HR from 130-140 although I’ve done extended time at 250ish watts and only usually have a 10BPM increase in heart rate. So from 200w to 250w it’s 140BPM to 150BPM but if I add another 50w and go for an extended time at 300w I’m usually around 165-170BPM.


At a guess, somewhere between 210W and 220W is where your lactate starts creeping up (LT1).

If you were doing a Z1 POL endurance workout, you’d be trying to stay nearer/lower than the 210W.


Thank you for answering, and excuse my ignorance… What is POL?

Polarized training (3 zone model/training)

Did your breath rate also increase to the point where you could no longer carry on a conversation easily? If so then that is another indicator that you cross VT1 and went into POL Z2.

For me, VT1 is right around 215-225 watts. I’m basically doing traditional base and trying to find that spot just below VT1 for long endurance rides.

What are you using for HR zones? Intervals.icu?

How do you estimate FTP for power zones? Ramp test? 8 minute test? Something else?

When in a ride does this happen? Any difference if the 230W section is at the start/middle/beginning of a ride?

HR response is not linear to power, so not hugely surprising.

I’ll answer everyone’s questions in this reply:

  • I base my zones on a 20 minute test, I’ve heard enough about ramp tests. I use intervals.icu and read stuff here in the forum.
  • I have played with different wattages, from 190 watts to 230. I am doing some “traditional base” and my rides are a warm up and steady Z2 for about an hour and a half.
  • I don’t lose my breath until I am at about 150 bpm. In the power ranges I’m talking about, I go from 115 to 135 bpm. For reference, intervals.icu says my threshold heart rate, calculated in an ftp test on Thursday, is 163 bpm.
  • I have seen the difference in heart rate about half an hour into a session. I have also started sessions with different watts and compared. Depending on how tired I was, the time of day, etc I notice some differences at the same watts, bit not quite as much as between 220 and 230.



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Last time I looked, Intervals.icu was using Friel HR zones. The Coggan HR zones for z2 are lower.

HR zones should be treated as loose recommendations, and need to be adapted for your situation. As you are using Friel zones, he stated that it is common for power and HR zones to not always be in alignment.

Thanks , I had overlooked it, I usually get lower HR zones than power zones .

I went for a Zwift ride with a friend who has the same power profile as I do but slightly higher heart rate, it’s interesting to check how different tools analyze what we did …

Coggan vs Friel HR zones for a 2 hour endurance ride earlier this week:

The average HR is my ‘all day HR’ and because of that I use Friel HR zones.