Zone 2 - what is it really? HRMax % vs cTHR vs FTP %

Hi folks,

I’ve been doing a bit of a deeper dive into the benefits of Zone 2 polarized training (which seems to be all the rage right now thanks to Pogacar’s coach) and one thing I’m struggling slightly with is the many definitions of how to get to HR zones that make sense.

My Garmin thinks my zones should look something like this (they are similar whether I do Max HR based or cTHR based w/ a max HR of 199 and cTHR of 180):

While SYSTM has me at this:

And not to be left out, Strava has me here:

The key difference being the upper limit of Z2 - with Garmin putting me around 138bpm, and SYSTM and Strava going all the way up to a heady 154-157.

I know that running vs cycling zones are somewhat different, but I’d be very interest to hear folks’ thoughts - particularly coaches. I would mainly love to know if I do have more headroom than my Garmin is telling me, as it can be pretty challenging to stay below 138bpm without pretty weakling wattage…



A small correction - i don’t believe ISM zones should be mixed with the polarised concept.
His zones are based on lactate measurements, but his z2 almost certainly falls within z1 polarised.
It appears likely the top of his z2 is approximately 80% FTP in professional athletes.

If you want to work out zones from heart rate i’d suggest doing an LTHR test and using the Friel zones (I think this is how Systm calculates it’s zones too).
You can use RPE to gauge if your zones are set well. For most people VT1 (the point at which breathing rate becomes noticeably elevated) correlates pretty well with the z2/z3 boundary.

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Apologies Andy, but what do you mean by ISM zones?

Inigo San Millan (Team UAE/Pogacar coach)

Zone 2 is just a label, the purpose of training in zone 2 is to improved aerobic fitness using a high volume of work to cause metabolic adaptations. This approach allows a much higher total training stress than could be tolerated by the equivalent work at Z3 or above. Making your endurance rides too easy ( i.e. riding at the low end if Z2 or even in Z1) is better than digging yourself into a hole of overtraining.

The upper limit of Z2 is not a fixed percentage of FTP, cTHR or MaxHR, it varies among individuals (I’ve seen people report as low as 65%FTP and as high as 92%FTP !!) . Its importance as a ceiling value is that fatigue build exponentially faster the higher above the Z2 ceiling that you go.

Strava just makes a dumb guess based on max HR calculated based on your age, ignore it.
Garmin and Wahoo(if you’ve done a HM of FF fitness test) are working off your data so are more likely to be accurate.

The only way to determine the actual zones are in a lab, measuring blood lactate and or gas exchange.


I’ve found something like the conversation test is the best way for me to find where the top of my zone 2 is. It makes sense as your zone 2 is defined in relation to your first lactate threshold or ventilatory threshold, which should be very close to each other. The conversation test is basically a field version of determining your ventilatory threshold.
Since I didn’t want to look like a madman cycling around talking to myself, I came up with my own version of this where I determined a comfortable breathing rate when I’m easy spinning at my normal cadence (breath in for 5 revolutions, breath out for 10) and when I can no-longer keep that breathing rate I know I’m hitting the top of zone 2. I’ve found this correlates really well with 75% of my FTP and 75% of my heart-rate-reserve and works really well for running too.


Thanks for everyone’s replies so far. So does it seem as if the best route forward is set my Garmin heart rate zones based on what SYSTM is telling me my zones are?

For the comments above on “mixing” polarized - my understand was that polarization is more around the concept of the ratio of base training (which occurs in ISM’s Z2, and Z1 in some other research depending on how many zones are being used) to threshold and hard efforts - with roughly an 80/20 split between Z2 and VO2Max efforts. My understanding is that SYSTM is a bit more pyramidal whereas true polarized is light on threshold efforts.

I’d be very interested to hear input from SYSTM coaches like @Coach.Rupert.H or @Coach.Spencer.R - I honestly hadn’t realized my Garmin was so different from SYSTMs HR zones until now :slight_smile:

Incidentally, the conversation test is what Iñigo San Millán suggests as a good rule of thumb.


I do exactly this! If I really, really need to get out for some headspace and force a z2 then there’s nothing better than riding whilst talking myself through things. I’ve solved personal and professional problems this way and you’re gauranteed to come back feeling good. It’s a great way to pass the time on what might otherwise be a dull ride, too.


Hi @Rearviewmirror - there are many different ways to estimate and calculate heart rate zones, and they all have some relative error. I’m always cautious to take what one source calls Zone 2 and compare it to what another source calls Zone 2 (there are huge differences in say the common Polarized 3 Zone model versus our Threshold heart rate determined 5 Zones in SYSTM). That being said, What Dr. San Milan calls Zone 2 and what we call Zone 2 are fairly close in agreement. Because we don’t have invasive methods (like blood lactate monitoring or oxygen consumption/CO2 production measurement) possible, we have our Zones based on either your Full Frontal or Half Monty results (unless you’re using the default values…which I wouldn’t recommend) and are going to be pretty close for most folks. Let me know if that makes sense.


Hi Sir @Coach.Neal.H - thank you very much for your response - I wasn’t expecting a response from you directly! Having just gotten back from a hilly walk where I could easily play with my zones, I definitely felt a “switch” occurring at around 158bpm+ (which is pretty much exactly where my latest Half Monty would put me and funnily enough very close to almost all my prior HM and FF tests).

That does make sense - now I’m just a bit mystified as to what to do with my Garmin devices as their heart rate guesstimations seem wildly off. I assume just updating the zones on my Garmins to match SYSTM is the best move, so that I can suffer appropriately across all my sports?

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Hi @Rearviewmirror - yes, we would recommend adjusting the zones on your Garmin to match your SYSTM zones…that way you’re comparing apples to apples! One this with regard to different sports - your cycling zones in SYSTM are specific to cycling. In most cases, if you’re running - then your zones are likely about 6-10 beats/minute higher when running at an equivalent effort relative to cycling. For something like swimming, then your heart rate zones when swimming are likely 8-10 beats/minute lower than your cycling zones. Let me know if that makes sense!


Thanks Sir Neal. It does indeed - massively helpful. I had spent a good amount of time Googling this, so having such a direct and clear response. So to make sure I’ve got the directionality right…

For cycling = Zone 2 = 127-157 bpm
For swimming = Zone 2 = 117-147 bpm
For running = Zone 2 = 133-167 bpm

This makes intuitive sense to me in terms of running gets my heart rate up for similar RPE.


Keep in mind that the cTHR is based off FTP and the Garmin zones are relative to MHR (or maybe even HRR & LTH). I’ve thought about editing the Garmin to match the SYSTM zones but the outdoor MTB zones aren’t going to be exactly the same as indoor training anyway so I’m not sure it makes that big a difference.

Not trying to hijack the thread but I have noticed while doing the SYSTM workouts, my actual HR is a bit lower than the target zones shown for each interval. I did the Full Frontal test about three weeks ago to establish FTP so I am a bit surprised that my actual HR is consistently lower than the training targets even though the power is being set by the trainer (KICKR).

Any thoughts about whether I should just plan to redo the FF test again in the next couple of weeks or adjust my FTP so that my HR is falling in the specified intervals?

I’d worry more about power than HR. The HR zones can be a bit off for most people in some workouts. That said, if you’re RPE and HR is consistently lower than you would expect for a given power then it might indicate retesting.


If you want to dig into the Inigo San Milan topic further listen to his interview with Peter Attia on his “Drive” podcast. There are also a few GCN interviews with ISM that are shorter and more to the point as well. The best way to find Z2 is lab testing. Short of that, at home lactate testing is good too. I just splurged on a blood lactate meter so I could measure myself. I figure it costs about as much as a single lab test and I can do it as often as I like. I’ve been able to dial in my power/HR so I am just at or under the 2mm/L recommended for the top of Z2. If you don’t want to purchase a lactate meter, one other method Peter Attia mentions is to calculate 75-80% of your absolute Max HR (flat out red zone end of a time trial HR), that will be your upper Z2. I found this exactly matches my blood lactate measurements.