Riding for hours in Z4 -- are my HR zones off?

I’ve tried a variety of HR zone calculation methods.

First was 220 - age for Max HR, which yielded zones that seemed like overestimates of my heart’s work (lots of time in Z4-5).

The second was a calculation for Max HR from age specific to female athletes. The zones derived from this also seemed like overestimates.

The third try was a calculation via LTHR estimate from Joe Friel’s blog. This calculation has raised the bpm ranges, but I still wonder if it is overestimating cardio. My current inputs are an LTHR at 174, with a Max HR of 190.

I read in a forum that if you’re riding for hours in Z4, there must be an error in the zone calculation. I can go for (outdoor) rides which are predominantly in current Zone 4 range. For example, in a recent metric century: 2 hours in Z4, 30 mins in Z5, 1 hour in Z3, and 1 hour Z2-Z1. Unfortunately, I do not have a power meter, so I don’t have that data for my outdoor rides.

Am I calculating HR Zones correctly?

If this info helps: my Max HR during the ramp test was 185 bpm (steady, not a spike). My RHR is ~52. All-time highest recorded HR (since I’ve started tracking HR) is 189.


My LTHR (160bpm) is also 92% of HRmax (175bpm), like yours, however my heart rate reserve is narrower (RHR 65 and Max 175).

What I found works…

  • use Friel’s 30-min test to estimate LTHR
  • use Coggan HR zones for Recovery up to Tempo (90% FTP, Coggan tempo)
  • at threshold (90% FTP) and above Friel’s HR zones

So its a bit “Frankstein” zones LOL:

Tempo (90% FTP) and below (Coggan zones):

Threshold (90% FTP) and above (Friel zones):

This was all done in hindsight, after buying a power meter. Friel’s z2 (131 to 142bpm) is where I start doing power based z2 workouts, but then over 4 or 8 weeks of early base my HR drops into Coggan z2 (120-133bpm).

Kinda wacky but it works for me, if I had to go ride without a power meter.


The 220-age rule is a very rough approximation and does not reflect the differences amongst us human beings. I would start by looking at your power zones and correlate that to heart rate. In my case, when I do sweet spot workouts, my heart rate is in the 150-160 bpm range. My resting heart rate is in the mid-40s. And the highest I have seen was about 180 bpm. When I go to my FTP it is between 155 and 165 bpm, although now I get very sensitive to things like choice of cadence and whether my power output is smooth and steady or spiky. When it is more spiky, my heart rate tends to be higher.

When I do an endurance workout such as Carter or Pettit, my heart rate stays at or below 120 bpm. But when I do the same workout after a demanding workout, it can easily be 135 bpm.

What I am saying is that in my experience at least, heart rate zones are much more fickle and depend on things other than just power output. I use it to gauge my fitness and fatigue levels, for example. But in my experience heart rate zones are way less useful than power zones.


Interesting, so you look at power and work back from there.

I suspect my indoor power and outdoor power metrics are different, but I won’t know until they start selling some cheaper SPD power pedals.

I think it is fairer to say that 220-age represents the average of the population as a whole, but like most ‘averages’ the MHR for any one individual can be significantly different from this. Indeed, the standard deviation for the age-based formula is 13.

In this case, there is a fair bit of evidence that @Samus’s MHR is higher than that predicted by the formula. Also, at 52, her RHR is lower than the assumption is the standard zone formula.

I’d suggest using the Karvonen formula for calculating zones, which takes into account RHR and MHR. And using 190 as the max HR. https://www.topendsports.com/fitness/karvonen-formula-calculator.htm

1 Like

I didn’t know the standard deviation for this, thanks for my nugget of information for the day. :innocent:

Let me ask you something: how useful do you find heart rate zones in practice (no matter how you compute them)? Sure, they roughly track power zones and knowing that my heart rate at this particular load is higher or lower than normal (i. e. normal for you) certainly is helpful to me. But given their inherent variability and the fact they are a lagging indicator, how do you use heart rate zones? :slight_smile:

What conclusions can you draw from that?

PS This is not meant as me nitpicking your post or anything, I’m genuinely curious.

1 Like

For me, HR zones are acting as a proxy for power, in both outdoor training and competition. I have the zones programmed to show up on my Garmin during rides. It’s easier to think in zones than it is to remember a bunch of different ranges.

At some point I will have a power meter, but again, I’m waiting on an SPD pedal meter that doesn’t cost a grand.

1 Like

Yes I’d use that, even though you only have indoor power.


I’m fairly confident in my LTHR and Max HR. I’ve looked over my historical data, and I would guess I’m within 2 bpm of the actual.

But I guess getting back to the main point, do you guys believe the Friel’s calculations are off in my case? Should I not be able to ride in Z4 for as long as I do? And how much do you think this matters?

I see.
Personally, I pace mostly by feel when I am without a power meter and use heart rate as an additional indicator. I did all races without (visible) power as I didn’t have my Wahoo computer back then. I only recorded power to my iPhone.

Perhaps for something long and sustained like a hill climb TT or a TT heart rate might be useful to meter your effort. If you have indoor power, I’d correlate power to heart rate, and work from there. But probably I’d still trust my feel more than a heart rate monitor.

I started training outside, without a power meter and HR was useful on long intervals from zone2 up thru threshold. So if I didn’t have a power meter, HR zones are more reliable for me than RPE. Also, I take an off-season and restart by doing zone2 by HR rather than power.

1 Like

I have a tendency to creep up in intensity as a ride goes on, and HR zones help me stay down in Z2 when I am supposed to be in Z2.


Z2 discipline can be a real issue!

Good point. This jogged my memory a little, I sometimes do the same when I do Z2 recovery rides on my mountain bike (which does not have a power meter).

Is a crank-based one not an option? 4iiii starts at under £300.

It’s not ideal. I’d like a power option that is easy to take off and/or move between bikes. It seems I’d have to do a custom install. It’s an option, I think.

Depends what crankset you have maybe. I’ve got the same sram gpx cranks on both my bikes, and the same pedals, so swaping the left cranks arm is actually quicker than changing pedals.

Presumably you weren’t riding in zone 4 for two consecutive hours though?

Total time in zone isn’t the same as “you can’t ride for hours in zone 4”.

So, whilst it seems from your zone distribution that you still spent an excessive time in Z4, it’s probably not out of the question that this time could be accumulated on a long ride if you’re well conditioned and doing, say, some longer well-paced climbs during that time.

A fair question.

I only got myself a power meter (Assioma UNO, later upgraded to a DUO) about 3 years ago. Prior to that I was training with HR only, so I had put a fair bit of time into trying to understand the nuances of HR. Now that I have a PM, I tend to use power as the main metric. I am more of a sustained power kind of rider, so the lagging indicator bothers me less than it might for a short power rider.

The 3 main things I still look at HR for are:

  • aerobic decoupling, sometimes as an indicator of aerobic fitness, and sometimes as a fatigue indicator on long rides.
  • seeing elevated HR on shorter rides suggests that I am not fully recovered, slept poorly, fighting an illness, and an indicator that perhaps I should cut that day’s training short and head home.
  • this afternoon’s ride was one of the first warm (32C/90F) of the (southern hemisphere) season, and I knew I wasn’t acclimated to the heat. It was only a zone 2 ride, and while I rode to the middle of zone 2 power, I kept on eye on HR to ensure it didn’t go above the top of z2 HR. In a few weeks when I am better acclimated, I’ll ride to power alone, but for now, I prefer to keep an eye on HR as well
  • z1 recovery rides I tend to ride to HR rather than power. Inevitably I will have to go above z1 power to deal with short climbs, steep ramps, etc. If my HR creeps into zone 2, it’s a sign I have been working harder than ideal for a recovery ride for too long.

In short, while I definitely ride to power, I tend to use HR as a guide as to when to put a cap on things, when power alone doesn’t tell me how my body is doing.


How are you measuring HR - chest strap (electrical) or wrist/watch (optical)?