Heart Rate & Power Info

Hi All

I know people have discussed power vs heart rate endlessly but I still haven’t found an answer to the below question so if anyone who understands physiology better than myself is able to answer this, it would put to bed a question I have had for a couple of years.

I am doing Zone 2 low level rides.
Power wise this equates to 146-198 watts
Heart Rate wise this equates to 116-154bpm

Whichever data you use, both are trying to do the same thing…work at a low enough intensity to improve your aerobic base which should build new capillaries, increase mitochondria and improve your body’s ability to use fat as a source of fuel on endurance rides.

This post isn’t asking whether heart rate or power is better, (I know why TR prefers power due to its consistency and that heart rate can be affected by numerous external factors) but my question is this:
If I use my zone 2 power to ride to (upper end 198 watts) my heart rate will rise to above 165bpm. How can I build an aerobic base if my heart rate is at 165bpm or higher?
That is 83% of my max heart rate.

(Extra info: I am 45 years old, 73kg, 172cm tall with max heart rate of 198bpm).

I guess what I am trying to understand is if we know what physiological adaptions we want from zone 2 riding and that these adaptions require plenty of oxygen to make them occur, how can power and heart rate zones be so different and elicit such different heart rate responses from the body?

Knowing the answer to this would allow me to understand which one would be better suited to me (and anyone doing low level training whose heart rate is much high when in a zone 2 power zone).
In the meantime I am sticking with heart rate zone 2 as this is the lower intensity so at least I can’t go too far wrong.

The past few years I when doing sweet spot my heart rate can sit at 90% max heart rate so you can imagine how long I last on Over/Unders.
This year I thought lower training initially to see if it helps when I get to the high intensity work that requires active recovery.

I’m not a physiologist so if anyone answers, please keep it simple…imagine talking to your 6 year old lol.

Happy riding all :slight_smile:


I’m assuming you’ve calculated your HR zones based off max HR. How have you determined your FTP? Ramp test? 20 mins test?

Do you have enough historical data to check that your power and HR zones do actually match? For example, have you done multiple threshold workouts and seen that your threshold wattage matches your threshold HR?

I would start there and then work backwards if it was me.

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I’ve done 4 twenty minute tests, 3 ramp tests, (ramp tests for me seem pointless as I over score on those and get readings that inflate the ego but practically are not useable) and 2 of the Sufferfest 4DP tests, (ugh)

However, my question was more about if two different sources of data are supposed to be achieving the exact same thing, (aerobic improvements with all the benefits that are attached to them), how can they be so different?.

I have seen other people with completely different heart rates and power numbers when also matching their zones so I don’t think I am unique.
I’m sure I read that when comparing HR and power, they often provide different numbers so not to expect them to match but that just leads me back to how can notably different responses provide the same outcome?

I will wait for someone to now use the phrase, ‘There’s more than one way to skin a cat’ lol.

It is my understanding that there is one aim here (zone 2 development) and 2 methods of measuring (HR and power). I suspect they’re “so different” in part because at least one of them may not be correct for you. If zone 2 power does not give you zone 2 HR then maybe one of these needs correcting.

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Little bit of info here that may be useful:

Seems to be quite a lot of data out there that there’s little to no benefit in working at the upper end of Z2 vs lower end. So if working at the lower end of Z2 power also means you’re keeping your HR in zone 2 then that seems a sensible approach.

Also agree with the comments above that one or both of your zones may be wrong. Personally I find quite a bit of variation in HR depending on time of day, temperature, fatigue, caffeine, etc so I tend to use it more as a sense check than as a metric to guide training intensity. Useful sense check on Z2 rides for me is whether HR is staying pretty constant after the initial warm up. If it continues to rise significantly while holding steady power then that’s normally a good sign that I’m working too hard.


That was my thought but I would love to understand the Why in order to be able to make the best decision.
I know TR push power due to the fact it isn’t altered by fatigue, hydration, temperature etc etc and that you get the same workout each time, (so far more consistent for controlled improvements).
But if that is correct, are they saying heart rate is irrelevant and just let it go as high as it wants as long as you are hitting the same power each time? And if that is true, how can a higher heart rate provide aerobic responses if it is 10-12 beats higher than a previous workout due to external factors?

Why what?

No. That’s why the workout screen gives you an HR reading. The podcast team have always (from what I can remember) recommended recording and monitoring heart rate, just not basing your workout intensity on it.

For what it’s worth. I also have concerns about HR being often discarded. Just because caffeine, for example, may elevate our HR, does that not mean that we should still heed this extra work that the heart is doing and adjust our riding intensity accordingly? I suspect the answer is somewhere between what is best for training and what is best for health.

And more reading here:

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Aerobic decoupling

Just skim read your posts between meetings - take a look at the link above to see if this helps.

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I think it’s more that they push power because the power curve and hence zones are more predictable from a single test than HR curve/zones are. The power you can put out is absolutely altered by fatigue, hydration and temperature - try doing VO2 intervals while tired, dehydrated and overheated! But all things being equal (i.e. assuming fatigue, hydration and temperature are in the same ballpark for your workout as they were for your FTP test) then having a decent FTP estimate enables you to have pretty decent estimates for the zones above and below threshold. Yes, there will be outliers who skew towards the aerobic or anaerobic end of the curve, but you’ll be close enough for most people. I’m not at all sure the same holds true for HR. For a start you probably need 3 data points, not one, to estimate zones - Resting HR, Max HR, LTHR.

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Well, primarily because they are just arbitrary selections of numbers at the boundaries. Additionally, the lactic acid & aerobic energy systems aren’t behaving like they are in a shuttle relay where the aerobic system hands off the baton to the lactic acid system at 199W and then grabs it’s shorts, bends over, & sucks wind while the lactic acid system 100% takes over. It’s more like rowing…they’re both in the boat & the lactic acid system starts to dip it’s oars in the water somewhere around 198W but the aerobic system is still pulling as hard as it can.

But you are doing the correct thing, IMO. Pace long Z2 rides by HR. Record power but don’t watch it. Also, I’d say ‘fatmax’ in cycling is a fairly new idea. Don’t assume that just because you are riding along at 70% of MAP (highest 1min power from a ramp test) that you can’t also be at whatever your Fatmax is for that day. On the other hand…next week your fatmax may be 40% of MAP. You could say fatmax can be all over the map…

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Go by power, your HR at Z2 power will sink slowly over time as you adapt. HR can be wildly variable based on a number of factors including phase-specific fitness. I’ve seen my max HR be 15 BPM higher when starting a phase vs at the end of a phase. I believe the coaches have discussed it, this is due to blood plasma volume increases with aerobic training

Power zone is almost the same as mine. I saw you prefer 20-min test for power.

How did you calculate HR zones? I did Friel 30-min to estimate LTHR and then used Coggan zones. My zone2 HR is 111-134bpm. For reference my LTHR is 160 and max 175. It’s hard to compare HR to others.

The adaptations you describe are in no way specific to zone 2. Basically anything other than true sprint or anaerobic capacity training will induce them. The only reason to keep the intensity down is to be able to do more volume, in hopes of coming out ahead overall.

I don’t know if it’s right or not but a few years back I used power alone and pushed to that but last year during chemotherapy I limited my self to HR (90% was working well). During both periods I improved but I feel like I did better when I wasn’t limiting myself on HR.

FWIW I am also 45years and a 175cm, 58.2kg Male with an absolute max of 200bpm, the highest I’ve actually hit in the last few months is 198bpm.

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I believe you were gifted and was a competitive cyclist? I was gifted with some serious math skills but athletically just an average Joe weekend warrior for 30+ years since graduating from college.

Being a student of my own physiology and a lot of experimentation, all I can say is that doing more zone2 work on a 6-12 hour/week budget delivered a) more sustainable heart rate reductions (shrugging), b) better power from 2-5 minutes (hallelujah and yeah baby!) , and c) easier path to higher FTP (can I get another amen!). That was from doing more zone2 versus TR’s sweet spot base, some details below.

@Day I’m interested in the physiology but train based on results.

I’ve had similar “problem” where a lot of mid zone2 aerobic endurance workouts will end up with zone3 HR (Coggan zone using LTHR).

Last year I did TR’s Traditional Base 1 and 2, mid-volume, with some repeated weeks as per the plan description. One interesting and unexpected result was that my heart rate decreased when doing 65% FTP (mid zone2 power) aerobic endurance workouts. It went from HR zone3 to upper end of HR zone2.

This year I’m working with a coach and started base training after 3 months of strength training. Still doing a lot of zone2 work (with some intensity), 2x per week strength (2 hours total), and 2x foundation / core stability work (about 1 hour). Total time budget for cycling+strength+core is 7.5-12 hours/week. Another side benefit of more zone2 is ability to combine strength and cycling, which is important after 40 and I’d say critical after you reach 50s.

This year on the trainer my 65% FTP (mid zone2 power) aerobic endurance workouts have FINALLY, after 2 months of base, dropped to mid zone2 HR. So instead of 128-133bpm the upper end of HR-zone2, its down to 117-124bpm the middle of my HR-zone2. Progress.

Z2 Power/HR is a key marker I look at when starting to train again. IE do both of them line up in steady state z2 efforts?

Aerobic decoupling: If I cannot sit at Z2 watts with a flat HR then I’m not ready to progress to more difficult workouts. (signaling to me that cardio system is limiter) After several weeks of Z2 work my cardio system will adapt, and HR will flatten and lower into Z2. Then I would move on…either raising Z2 watts or starting sweet spot (muscles are now the limitors).

This year I didn’t take time off and instead just went into sweet spot base after some volume of summer riding. Over the past 6 weeks my HR has dropped 10 BPM for 90% efforts and last weekend I did the 90min sweet spot workout and experienced flat HR for the efforts. Good indicator that an FTP bump is in order when sweet spot feels like tempo.

I also noticed that Z2 power (for me I check power @145bpm) has gone up about 20 watts. RHR has also gone down 2bpm since late summer.

So yeah, keep track of HR but do your workouts with power. HR will do its thing…it should lower with consistent training and be more inline with what you think your zones are. Also, keep in mind that neither of these scales are fixed.

Keep at it! Good luck!

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I was just speaking in generalities, since the OP seemed to harbor some misconceptions re. the effects of training in different zones and what role, if anything, an elevated HR plays (answer: none).

Thanks for you help.

Yep I am aware that zones work in curves and phase in and out of one another with associated benefits also fading in and out. Energy systems for strength training works in the same way.

Just read more about fatmax and that all makes sense. As with most things fitness related, it seems very personal and adjustable depending on other factors. But the fat utilisation was just one reason for the Z2 work.
Last year I made little progress doing the SS base work and then struggled all the way through sustained power. My heart rate maxed out and wouldn’t come down before the second interval blew me out of the water and I had to stop.
So I thought this year I may try a longer base block, (3 months) and see how that sets me up for SS later.

Fingers crossed :slight_smile: