Zone 2 Power vs Zone 2 HR (Should I increase power to move HR to Z2?)

I bet your RPE went up as well.

Yup. Just checked my Garmin. It was 66f on the coast an hit 104f in the canyons. 7000’ of climbing and I was on the struggle bus @ 200w.

Corner case for most. Especially for everyone focused on indoor training in controlled temps. Over here I see pretty good swings in temps but not huge changes in HR.

for the benefit of others… oversimplifying for zone2 power the subject of this thread you have:

  • a baseline HR for a given power
  • once temps got hot enough there will be increases in HR and breathing to pump blood to your skin for sweating
  • muscle recruitment changes over time may increase oxygen demand thereby increasing HR and breathing

Your leg muscles may still be doing zone2 work, even if HR drifts above that for cooling/sweating. A heart rate increase doesn’t mean your muscles are magically doing the same work as tempo or sweet spot or threshold - you may in fact be primarily burning fat and not carbs.

IMHO the real question is a training question.

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I can’t imagine anyone would imagine there was a correlation between higher HR and workload?

On another note. How do bike computers calculate calories burned / Kj expended? I ask because I assume it includes (amongst other things) power. But if your PM is inaccurate does that mean so is your workload? Or is it based on a % of FTP?

People do all the time.

Normally it’s power meter kJ work to kcals. Wahoo Bolt did some funky stuff in the past, if something wasn’t set properly. I don’t recall the details.

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A couple of articles on it:

How Accurate is that Calorie Reading? | TrainingPeaks

How calorie measurement works on Garmin fitness devices | DC Rainmaker

Looks like Garmin have done the typical garmin thing and added resting calories into the mix so their numbers are different :exploding_head:

“Calories burned” vs Work (kJ) - Garmin Connect Web - Mobile Apps & Web - Garmin Forums

HR is affected by many variables - zone 2 is higher in summer than winter for me for HR due to changes in temperature). Power if your FTP and zones are set correctly doesn’t lie. Watts over HR as far as I’m concerned…my HR is low in zone 2 as well


Yea I won’t lie I mostly wanted to use heartrate because I can use a higher power in zone two and in return test my patience a lot less. But I agree the power is power.

Seiler does… he calls power external load and heart rate is indicative of internal load and internal load increases during exercise…

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Hypothetical; your goal Is to do a 4 hour endurance ride. You do two rides- Z2 power for both. The first, breathing and HR is normal, RPE is low. The second, HR is close to threshold, breathing is elevated and RPE is higher.

How do you feel after after each ride? And do both rides meet your intifial goal?

I live in Florida and this time of year the first half of my ride I’ll go by power zone 2, then once 9:30-10am rolls around. The temperature is at least 90° and my heart rate creeps up, that’s when I start going by my heart rate zone 2.
From what I understand, heart rate is the internal load and the higher that load is the more recovery needed. Sure the legs might be in zone1/2 for the long ride but if my heart rate is zone 3, I feel recovery takes a bit longer.
That’s my personal anecdote, I still don’t know what is best, follow only power the whole ride; or do what I’ve been doing?

Fortunately (apart from about a month ago when we got 42C in the UK) I don’t live where temperature fluctuations are so great that it massively affects my HR. If I do a zone 2 ride@200W in February my HR is usually about 105-120bpm, same ride in July HR is about 115-125bpm but they both feel pretty much the same. That said as a short distance TT rider and runner I don’t usually do more than about 3 hours, maybe if I was doing 6hour rides I would notice the difference in fatigue more.

I agree this is a training question. So the questions are:

  1. What adaptations are you looking for during Z2 rides?
  2. Do you lose that training benefit when your heart rate rises above Z2 because of heat?

When these training zones were developed, were they targets or guidelines? What I mean is this: Some trainer, long ago and before power was ubiquitous, told his riders to stay within a certain heart rate range for these long rides. This correlated to whatever power.

Once power came on the scene, coaches started giving a range of power and this was then also correlated with heartrate. But as we know, that correlation isnt a constant and depends on many things. So which is more important to follow?


I could definitely be wrong but I would think so the opposite? Because the temp will impact the HR so go to power when it gets hot?

I wish I could transport to Florida for my zone 2 rides(minus the heat) to get some flat miles

Seems like a simple question but I’m glad I’m not the only one with it.

I think that’s where people say using a combo but I don’t see how that works when they aren’t in line with each other.


Runners don’t have power meters and so they go by heart rate afaik for zone 2.
My instinct says go by heart rate with heat fluctuations but I’m not a coach.

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  • I know some that ignore HR and go more by pace and RPE.

Overall point being that there are multiple solutions that work for different people based on a range of factors so this applies to cycling, running and who knows what else.

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I think one crucial factor that has not been discussed in this thread, is time. Time is a huge factor, at least for me when doing Z2. Just like there is a lag in HR response doing VO2 and Threshold work, it appears to be the same for endurance.

For me personally, a typical 1 hr set at top range of Z2 power does not get my HR up there, but it is creeping towards it! Drag that out to 2 hours and it’s there! Many of the TR workouts in the plans for Z2 riding is in the 1 - 1.5hr range. So not that challenging for someone with a good base, and a correctly set FTP.

If I recall correctly from the Fast Talk podcast, the way to make the endurance workouts productive is to stay in Z2 until you start seeing a significant drift in HR, however long that will take.


Imo thats not HR lag it sounds more like decoupling. I might have misunderstood though
HR lag is typically seconds to maybe a minute at most.
After warmup of course.

How and what I use to pace my Z2 work depends on the main focus of the session. Which is normally a mixed of adaptations and fatigue management. More often than not I use pace, HR and RPE or Heart rate, RPE and power.

HR is normally weighted as slightly more important for me most of the time for Z2 work.