Correct. Those are %MHR (alternatively base on LTHR if you know it). None of this I would base on power or %FTP as primary.
(The PD curve has never accounted for fatigue)
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IF refers to FTP (it is the ratio of normalized power to FTP to be precise). However, I use heart rate, because I did most of my outdoor endurance rides on my mountain bike, which does not have a power meter. Even if it had, I find pacing endurance rides by heart rate better, it is more relaxing since heart rate does not fluctuate as much.
The power-at-given-heartrate curve changes with fitness, so the power is actually trending up as I get fitter, but there are other factors such as heat and humidity. But from experience, I’d say the power levels I reach are at most in the very low 60s (as percentage of FTP).
Overall, the easy rides should be really easy. TR ups the intensity on endurance rides simply because it has no other option. I just can’t do a 4-hour endurance ride during the week, I’d have to get up at 2:30 am 
I understand, I just wondered if you’d crossed wires as you said 72-80%MHR is too hard, but then also said that you ride 130-135bpm. Of course I don’t know your Max HR, but with a bit of an ASSumption I figured that’s probably in the 70’'s.
Anyway, enjoying following the conversation and felt like you were adding value to what was being said. I just wanted to confirm my own numbers really as I’m using 130bpm too for “high easy” or an LT1 approximation, but for me that’s 77%.
Sorry about the confusion.
Pretty close, my max heart rate is 178–180 bpm, so that’s in the low-to-mid 70s relative to my max heart rate. When I am very fit, I can ride 70 % of FTP at 130-135 bpm in the spring or the fall. (Japanese summers are hot and humid, and my heart rate tends to be higher.)
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Once a month: over 3-week loading period increasing 4 → 5 → 6h, going by HR at ~140bpm with LT1 HR being 146bpm. This is with current SusPBHV plan, I’m substituting weekend SS workouts.
I happen to have same range 
I’m sniffing around this topic because planning to continue with POL plans for rest of summer. Did also last year but then I definitely overcooked easy days by chasing IF 0.65-0.67 and FTP actually stagnated.
Anyway, thank you everybody for input. Will continue upcoming loading period as is (with HR slightly below LT1) and depending on results may try next one easy days right at it.
I too use heart rate together with RPE and can I have a conversation for my easy pacing. I got some interesting stats from a regular flattish route I ride at an easy pace.
Back in November 21 at my easy pace on a particular 5 hour route my average heart rate was 117 bpm. On Sunday on same route at same overall average speed my average heart rate was 93 bpm. My max heart rate is 170 bpm on the bike I was riding. Thus for same pacing on same route in similar wind conditions my heart rate dropped from 69% MHR to 55% MHR over the past 7 months or so.
You’re probably wondering why I didn’t increase the pace to sit around same heart rate as Nov 21. Simple answer is that I was towing my wife round the route as she builds up her own bike endurance. Easier than what my new easier pacing would normally be but I was happy with that as it allowed my wife to do her easy pace as well.
In terms of heart rate I put an absolute cap of 75% MHR which is sometimes seen on a longer hill. But generally I’ll sit around 70% and often around 65% MHR. But I don’t have a problem if I’m around 55% and I’m helping my wife with her cycling.
The way I see it is that the improvements from the easy rides takes volume and time and consistency week in week out. If I tried to measure improvements in weeks I’d be disappointed. But when you look back over months or years you see how far you’ve come.
Looking at my heart rate range of my easy rides over past 7 months I’m generally keeping it between 60-70% of max HR. But if I have a few minutes during a long ride where it’s crept up to 75% max HR I don’t stress about it.
The key for me, for the easy ride, was letting the ego go when someone overtakes you. The temptation to up the effort is always there, particularly uphill. You have to let that go and settle into a zen like calm.
Above it was asked how regularly someone does a 6 hour easy effort ride. At this time of year (summer here) I’ll do a 4-6 hour ride every week as my long ride, apart from recovery weeks.
Do people who are pacing by HR account for cardiac drift due to changes in ambient temperature and/or humidity?
Yes, but I try to be enough below that a bit of drift is not going to be an issue anyway.
Only ever consider it if a session pushing up to the cross-over to the grey zone, which it rare as I like to be safely below LT1 if that is the idea behind the session.
This is my first summer to go by HR, so have no strategy yet but I’m going to try keep absolute HR number: during ~2 week heat acclimation period power will be lower. After that hopefully returns to usual levels 
Assumption is that body as a whole does more work in hot/humid environment and easy day intention is to keep it easy enough for better quality power-based hard work.
When pacing by HR, cardiac drift means your power will go down over time, your heart rate won’t go up, as that’s what you are pacing off. If your RPE has significantly changed for that heart rate it’s time to head for home.
yeah, that is why I do endurance rides off power not HR. Where I live is hot and humid and temps can vary 20-30F from when I begin and end a ride. With pretty stable power over a 5 hr ride I still get pretty significant cardiac drift just due to heat and slight dehydration. Hence why I don’t understand the HR pacing unless one’s environment is more stable than mine.
But by going off power you’ll drift out of easy and above your LT1 unless the power was conservative to start.
How would cardiac drift from thermoregulation and mild dehydration push me from below LT1 to above it?
Long discussion on LT1 here:
I think I can compare 4hr indoor rides over the winter with minimal cardiac drift (stable 65F) to similar length outdoor rides in the summer (start 65F to 85F at end) with similar NP where I have much more cardiac drift. Sure, power is a bit more variable outside and I’m not able to compare rides 1-2 weeks apart, but I have rides I can compare that control as many variables as I can.
I understand that if one is pacing based on HR that power will decline over the course of a ride as more motor units are recruited and cardiac load increases. My question was about if / how people compensate for increased cardiac load due to thermoregulation and slight dehydration because: 1 - HR increase due to those (thermoregulation / mild dehydration) factors does not indicate fatigue or increased motor unit recruitment (as far as I know), 2 - the main benefits I am interested in from long endurance rides come towards the end and am I reducing the benefits I am aiming for by unnecessarily reducing power (after I already put in hours of work to fatigue slow-twitch fibers just to get to the point where I’m getting the stimulus I want)?
I don’t ride in a polarized fashion nor pace off HR, hence my question for others. I, personally, think there are too many factors that vary day to day to make HR pacing something I want to do.
Consistency, volume, recovery, and hitting my hard days hard are not issues I’m facing at the moment.
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I use all of it all at once. All the time. I constantly make game time decisions as to how fast to ride. It’s not whimsical and the most challenging part is being honest with yourself. I come in either at the low end of Zone 1 (norwegian 5-zone), or the upper end of Zone 2 (norwegian 5-zone). I used to be more specific and found it to be a false precision.
“Don’t dilly-dally”. “Stop standing and hammering”. “Endurance on the flat, tempo on the hills”. “When the road turns up, go easy, when the road goes down, go hard”. These sort of folksy training soundbites like I’m as old as LeMond occasionally help keep me on track.
If / when I ride harder, it is intentional, sometimes structured, sometimes not.
I don’t ever come in from a hot humid ride and wonder why my HR was high. It’s obvious. 
I did the work. Rest up, rinse, repeat. Pretty boring on paper.
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Yes, of course you need to account for that. But if you want to accumulate endurance kilometers, it isn’t important to hit precise power targets, but to moderate yourself and keep it very easy. That means right now in Japan (34 degrees, very humid), my endurance rides are more mellow. But speed isn’t the goal, so that’s fine. And hitting power targets precisely isn’t important either as long as you stay solidly within Z2 for almost the entire ride.
My heart rate targets change a little depending on how fit I am, the weather and how I feel. Some days I will enforce a cap of 140 bpm, others 135 bpm.
I think there are pros and cons to both. Personally, I don’t have a choice, at least when I ride my mountain bike — it doesn’t have a power meter. Even if it had, I want my outdoor endurance to be relaxing, they should feel easy. They should be a reward, not a chore.
Also, given the summer heat and humidity here in Japan, if I were to pace off of power, I might accumulate a lot more fatigue. For endurance rides, I’d like to avoid accumulating a lot of unwanted fatigue. I remember last year on the hottest day, I did a crit race and cycled 70-80 km each way to and from the venue. On the way back, I was crawling and even though I was very fit, my heart rate went through the roof (145+ bpm at under 200 W when my FTP was 340ish W).