HR during Z2 - when do you call it?

Have a question that I’d love to get the general consensus on.

2 hours of Z2 planned. Right around 70% FTP. By the hour mark my HR is in threshold range, around 85% of my max HR. What would you do?

A. Finish out the planned workout, HR be damned. Push through it and stay on power.

B. Knock it down to get my HR back to endurance level. Regardless of power, keep HR capped.

C. End the workout altogether. HR is too high, and it indicates I’m too tired. Get some rest.

I hope it doesn’t turn into another HR vs power on Z2 debate. Just wondering what you guys would do.

Edit: Also, I did 2 hours at the same power yesterday and my HR was 25BPM lower.

Any option except this one.


just slow down. its endurance. endurance is not a %%%. just ride your bike. its no more complicated than that. ride your bike


i was doing a polarized TR plan. it was giving me lots of 0.7 ish IF rides. i could do them, and i was. but in my heart i knew they weren’t endurance. i called them moderate, because they were. they were no better than 0.55 to 0.6, but they carried fatigue. i wish i had just ridden my bike those days


I would decide choose between A, B, and C based on my perception of the effort, keeping in mind my plans for the near future.


25bpm difference is huge. If no clear reason (hydration/fueling/temperature), I’d assume sickness and turn back home.

But in general, I have 3 approaches:

  • recovery ride: simply keeping legs moving, high variability but keeping power in Z1/Z2. Usually neighborhood discovery rides (a la pushing short distance score up)
  • weekdays 2-3h: going by power (65-75% of FTP)
  • weekend long rides (4h+): HR capped (with my self selected cap, it makes ~ 57-63% of FTP)

EDIT: I guess it also depends on your riding style: if you do fartlek (anything goes and average it to be Z2), then it really does not matter, just gather your hours of fun :slight_smile:

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In that scenario I’d do B or C purely because if my HR was that high with a Z2 ride I probably wouldn’t be feeling that goods anyway. My heart rate only drifts that much at the end of 4 or 5 hour group rides that, whilst the majority of them are in Z1/2, they kick off with monotonous regularity as and when someone is feeling good.


Personally I just don’t find HR useful, so I would ignore it. But instead I would pay attention to how you feel. If the legs aren’t working one day, then knock it back or cut it short. Focus on getting back to a sensation of strength for the sessions to come.

I can also have 20+ bpm swings between similar workouts. Doesn’t mean I’m sick, stressed or fatigued. It doesn’t really correlate to how I actually feel.


Stop looking at my HR, finish workout by power and feel. If it feels too hard, reduce target power or finish up.

There’s lots of reasons Hr could be high, I might check my sleep and Hrv trends for example after the workout. I might check the graPh and batteries.


If it’s hot and humid, my heart rate will be 5-10 bpm higher across all zones. Other than that it’s another reason I’m echoing riding by feel and RPE especially for endurance.

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Is this an actual experience or hypothetical? Does HR in the threshold range feel like threshold?

My take would be that the rider isn’t very fit (cardiovascularly). Or, there is some other circumstance like others have mentioned (humid, dehydration, etc).

Other ideas:

Seiler has said many times to do Z1 under the VT1 (estimate 65% of HRmax). I actually did this for a base season. At first I was riding ridiculously slow to keep my HR under 125bpm. But, by week 7 I was riding much faster at the same HR and breaking all my PRs on Strava segments.

I tested my VT1 with DFA alpha1 (HRV) and it did confirm Seiler’s 65% estimate. Actually, I was 130bpm when fresh and 125bpm under normal training, and maybe 120bpm when very tired. (Yes, I know that DFA alpha 1 may not be all that precise but it was an interesting experiment and confirmed Seiler’s estimate and the talk test estimate).


First off, yes this was the actual scenario from this morning. I did two hours at 70% FTP yesterday, felt good. HR was in mid 120s to low 130s. HR max is 185bpm.

Today hopped on the bike with same planned workout. By the end of the hour I felt not as strong as yesterday but not bad. HR was in high 150s. Decided to knock it back down to get my HR around 130bpm, which ended up being around 50-60% FTP. Again, legs didn’t feel overly bad or weak. Not super fresh (I felt stronger yesterday), but nothing that would make me think about quitting.

Same HRM. Both days indoors on the trainer.


It depends… (as always),

Reduce power see if HR stablises, if not call it.

Then workout what happened and why and use that information going forward.

Plus, 70% might only be reasonable on a fresh day or 80% or 60%, depends on your aerobic capacity.

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It kind of does mean one on these though :thinking:, it is the truth, too much heat stress, not enough rest, training at a level you are burning carbs that are becoming limited, dehydration etc. It is Always one of these, or something I forgot to mention.

Ignore it at your peril, you’ll work it out, eventually, or never realise anywhere near your potential.


That’s what I would have done. If I’m in the 150s on a zone 2 riding I’m working too hard or something else is going on with my body.

In addition, for zone 2 I’m going to err on the side of knocking down the intensity.

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I’ve been training and racing for over a decade and it just doesn’t correlate with those things for me. It might for some other people, but it doesn’t for me. I’m very aware of how I feel day to day, when I need to take an easy week, or when to push through and not be beholden to numbers. HRV is even more useless in my experience (again, it may work for some people though).

I’d urge riders to note how they feel, rather than putting unquestioning faith in the numbers. If they have a strong correlation then great! But if they don’t then just go with the sensations.


Something way off there. Two hours of Z2 certainly shouldn’t impact the same workout next day. That’s a huge difference and something else was going on to cause that. What has happened between the two sessions, and what was different environmentally? Only you can answer those questions.

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I probably wouldn’t make a decision based solely upon one metric- my goal with z2 rides isn’t to hold a particular output, it’s to do some relatively low-intensity work in such a way that it doesn’t significantly impact my key sessions. HR numbers can provide some guidance and feedback on that, but they’re neither a perfect reflection nor a primary determinant of how well I’m achieving that, so I’d probably take it into consideration and make a decision based on RPE and overall context (upcoming sessions, what else is going on in my life, etc.)

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Which criteria would lead you to choose option A?
Which criteria would lead you to choose option B?
Which criteria would lead you to choose option C?

Really interested to get your thinking here!

Just ride endurance by Heart Rate and don’t worry about the power.