Suunto ZoneSense

Brad_Olwin

@Zdeněk-Hruška from a scientific perspective, ZoneSense is nothing more than a theoretical concept and a marketing move rather than something really useable in its current state. The principal behind it works but it is too unreliable in its current state. Even under perfect “lab” conditions accuracy is not good enough to be useable for most people, especially not on individual runs as they market it. Maybe in the future…

Made a summary of a recent scientific study with a link to the publication testing ZoneSense, in the thread below.

https://forum.suunto.com/post/175109

@Josaiplu “Study” by Nakan is somehow useless because such a study has already been performed with way higher n-number by the experts that developed ZoneSense. I can also only put it in the category of marketing…

I read the paper and disagree with you. DDFA is within 10bpm with a 95% confidence limit. I fail to understand why DDFA is so unreliable. Suunto did not state that ZS was a method for determining zones effectively. Instead, ZS is marketed as a tool for real time measurement. The authors clearly state “ The DDFA-based method offers a simple and accurate alternative for the estimation of the AeT and AnT, which can be implemented in real-time monitoring of the training intensity during exercise”
I completely disagree with “ ZoneSense is nothing more than a theoretical concept and a marketing move rather than something really useable in its current state.” Do not understand what you are looking for. How do you want to use ZS? Clearly ZS has limitations. I would not use ZS for short interval training (less than 10 min) but I use it extensively in long runs on trails where Pace and Power are utterly useless and HR isn’t great either.

Brad_Olwin

This post is deleted!

Brad_Olwin

@soisan After watching the videos I think Suunto does mention shortcomings, in the app the wording is very careful about whether or not you should change your zones. I agree that the short marketing videos are just that, marketing videos.

brave_dave

@Brad_Olwin It has a MEAN absolute difference (median error of means) of ±10 BPMs and a 95% confidence interval of around 4 BPMs. Meaning that for most of the 58 tested subjects the estimated value deviates by 10 BPMs and 95% of all tested subjects are in the range of 6-14 BPMs deviation. The data points also seem to be gaussian distributed. So for only less then 5% it has a lower deviation of around 6 BPMs and for some of these 5% it has even a deviation of more then 14 BPMs.

Of course, accuracy is highly subjective…but statistically seen, from the available data that I have, I do not use ZS at all.

For me personally, when I know that on average, even under perfect conditions, the ZS estimated threshold is off by 8-10 BPMs in either direction, it is not usable for me. Even the authors discuss that there set-up is highly artificial and it needs to be seen if it even works under normal run conditions and without exercise until exhaustion…also 10 BPMs above my threshold is for me all-out running for 1km while 10 BPM below, is the HR that I have on the first kilometers of a Marathon. For me that is just way too much deviation to rely on it for proper training control and also dangerous for people that believe they can trust the value and base their training on.

That I am not the only one this applies to, is already reflected by the statistics and the numerous posts from people in this forum that struggle with the value that ZS gives them and are looking for help to understand and interpret it.

Communicating the average accuracy under perfect conditions to the average non-expert consumer, would already help them a lot to interpret the value for themselves.

For the future, I am looking forward to more data and studies and maybe an improved algorithm, as the concept is really nice! But right now, it’s not there yet, in my eyes.

Josaiplu

Zone Sense: Practical Questions for Confirmation

Dear All, I have some questions about Zone Sense usage and baseline management that I’d like to confirm with the community ( I have read most of the thread but it is pretty long so sorry if I have missed some already replied question, maybe a sum at the beginning could be helpful)

1. Managing the Initial Calibration Phase

I understand that Zone Sense requires approximately 10 minutes of warm-up before providing accurate readings.

My specific situation: I do trail running and my routes start with a 5-6 minute climb right from my door before reaching an undulating plateau.

My question: What’s the best approach to manage this initial climb?

Should I intentionally go very slowly during this climb to allow proper calibration, even if it feels “too easy” (like walking when grade is higher than 15%) ?
Or would it be better to add a 5-minute flat warm-up before starting the climb?
Does starting with high intensity during this calibration period negatively affect Zone Sense accuracy for the rest of the workout?

For sure If I ran the first climb at a good pace it will make my data faulty for the rest of the run at least it is my impression.

2. Baseline Storage and Memory

My understanding: Zone Sense stores a personal baseline that improves over time with each workout.

Questions for confirmation:

Is the baseline cached in the watch between workouts, or does it recalibrate from scratch each time?
Does each workout contribute to updating this baseline, or only certain types of workouts?

3. Sport-Specific Baselines

My question: Does Zone Sense maintain separate baselines for different sports?

Context: I do both trail running and cycling (alongside others sports but those are the 2 main one) . If I do easy cycling sessions, will this help improve my Zone Sense baseline for trail running, or does each sport have its own independent baseline?

Would easy rides on the bike contribute to better Zone Sense accuracy during my trail runs, or should I focus on doing easy trail runs specifically to build that baseline?

Any insights from experienced Zone Sense users would be greatly appreciated!

Brad_Olwin

@brave_dave I do not use ZS to set thresholds and personally I do not think that is the intent as I have stated before. I primarily use ZS in real time to assess my effort and as I have stated before it does a phenomenal job of matching my RPE. As far as I am concerned RPE is a far better estimate of effort than any thresholds I have obtained via lab testing or individual testing.

Second, I would argue that any lab test is going to have at least a 5bpm or greater error so that would be 10bpm around the median for the test. I find it rather surprising that anyone would believe their LT or AT is an absolute, our bodies do not work that way.

There is no way that 10 bpm below my LT would be a marathon pace, and 10bpm above is definitely interval effort.

So the point of ZS is not to set zones but to assess effort in real time, it does that well for me and for others. Given the lag in ZS (a couple of minutes) it is well suited for endurance efforts and not well suited for shorter efforts.

sky-runner

@brave_dave said in Suunto ZoneSense:

For me personally, when I know that on average, even under perfect conditions, the ZS estimated threshold is off by 8-10 BPMs in either direction, it is not usable for me

It is way worse for me. I’ve seen example of ZS suggesting anaerobic threshold that is even below my aerobic threshold - that is almost 30 BPM below what it should be. These are laughably inaccurate estimates.

Let’s look at another example where I actually had a steady threshold effort for a long time that was a good indicator of my anaerobic threshold. ZoneSense still managed to detect my anaerobic threshold at 148 even though I ran for 20 minutes in the 160-165 range. By the way, that closely matches multiple of Garmin’s LTHR estimates that all detected my LTHR at 162-163. How ZoneSense managed to detect that at 148 is beyond my understanding. I can’t seriously trust that at all.

Doodoo Runner

@sky-runner this reviewer did lab tests along with ZoneSense . Among his group was DC Rainmaker. The findings suggest Zonesense is not to be trusted.

https://youtu.be/17JcMg_oxy8?si=ojoVFGcIyMM5YbY4

gone troppo

I only ever look at zone sense in the app after a workout, I have found it wildly inaccurate at times and others fairly accurate. For me the gold standard is RPE followed by HR however even HR can be misleading as I’m often training fatigued and when doing an hour long effort at near threshold in terms of RPE when fatigued my HR might only be in high zone 3. When fresh HR seems to align better with RPE. Zone sense has often shown nearly all green with a few tiny spurts into yellow when I’m at 9-9.5 RPE doing a threshold effort up a vertical kilometre!!!

A Former User

@Doodoo-Runner said in Suunto ZoneSense:

@sky-runner this reviewer did lab tests along with ZoneSense . Among his group was DC Rainmaker. The findings suggest Zonesense is not to be trusted.

https://youtu.be/17JcMg_oxy8?si=ojoVFGcIyMM5YbY4

curious to know why, with the same HR source, the SV and SR results differ.

MarkusG

This reviewer did a lab test along with ZoneSense and came to the conclusion that it’s very good:

https://www.youtube.com/watch?v=G9Sr0-Ig_oQ

Written form: https://www.nakan.ch/wp/2025/09/17/tout-savoir-sur-zonesense-de-suunto/#Conclusion_sur_lalgorithme_ZoneSense_de_Suunto

Just to show that in today’s world of influencers it doesn’t take long to find someone who claims the opposite.

ChrisA

@Brad_Olwin I agree - it’s the real time feedback, that is most valuable and for me too it really corresponds on how I feel. I used to train a lot by HR Zones and sometimes it worked great but often I felt they were too low to or too high compared to my set zones (having had a tested LTH).
With Zonesense this feels much more ‚realistic‘ and actually Zonesense for me is (besides others) one of the features why I would never use another brand.

brave_dave

@Brad_Olwin I don’t really get what you want to convince me of. I am just stating scientific facts and want to point out that the accuracy of ZoneSense is just based on anecdotal information like yours and that the scientific data rather hint to a too high inaccuracy to recommend it for training control on a population level. Therefore, users with strange data should not be unsettled that they do something wrong in their training.

szleslie

Is it possible to turn Zonesense off in the app (iOS). I do not use it. Unfortunately it set default in the graph.

brave_dave

@MarkusG big problem of our modern society where everyone can just spread unverified and anecdotal information! Better rely on verified data from independent researchers and experts. But apparently there is too much money to make with just claiming that you have developed something special. Garmin is the worst example with their “body battery”, “heat/height acclimation”, “Real-Time stamina”, “endurance score”, “training readiness”, “running tolerance”, “race predictor”. Nothing of that has ever been scientifically validated that it actually works and every good coach and athlete can do more accurate race predictions

VoiGAS

Is still something happening with Zonesense? I don’t think it is mature enough to stop development. Or maybe its in a dead end?
Apart from @brad_olwin there are not many reports about the feature working.
For myself I am using it to verify my HR and Powerzones from time to time. Just comparing Zonesense TSS with TSS(HR) and TSS(p). But real time its still absolutely random
(New belt, new battery, moistened with water and gel, 10min slow intro, tight fit and sweating like in hell)

raven

@VoiGAS said:

Is still something happening with Zonesense? I don’t think it is mature enough to stop development. Or maybe its in a dead end?
Apart from @brad_olwin there are not many reports about the feature working.
For myself I am using it to verify my HR and Powerzones from time to time. Just comparing Zonesense TSS with TSS(HR) and TSS(p). But real time its still absolutely random
(New belt, new battery, moistened with water and gel, 10min slow intro, tight fit and sweating like in hell)

I’ve found ZoneSense to be interesting but problematic. First, the ten minute calibration I’ve found needs to be managed carefully. You can’t go too hard, but nor can you go too easy, or else you’ll get problematic results. I normally consider my AeT / LT1 to be 144bpm, but yesterday doing a Wahoo SYSTM structured indoor bike workout ZoneSense thought it was 122bpm, as the workout featured a very light warmup. With a proper warmup it’ll give me my expected result, are very close to it (e.g. 140-148bpm range).

Because it’s a lagging indicator, interval sessions sometimes don’t even register. A track workout of 400m sprints, with 400m walks may or may not register; 100m sprints almost certainly will not.

For an indoor rowing workout, where sessions might only be 10-20m with short intervals, the calibration time takes most of the session, the intervals are too short, and I can’t really glance at my watch during the session so it’s useless for that modality live. If I do a longer 20-30m session, starting steady-state for the first 6-8m at 120w, then increase to my rowing FTP of 160w for the final couple minutes of calibration, that tends to work decently to get it right but I still can only make note of the data after session and not during.

I find it best in running as a “secondary indicator” after normal HR when returning to a longer, slower effort after a harder push. If I do 1km at a threshold effort, then return to a lighter effort, I’ll first notice my HR dropping down to zone 2, then about a minute later ZoneSense will return “green,” and sometime (typically when weather is hot), I need to dial down HR a bit more, so rather than settling in at say 140bpm I’ll go a little slower and get to 136bpm and then ZoneSense will be happy.

At this point though a lot of this I’ve internalized as RPE so looking at ZoneSense “live” during session I don’t typically need. Now, if ZoneSense could “remember” say my last week/month of data, and use that as “temporary, provisional” info while during the calibration, then that might be helpful but I suspect that’s against the philosophy of what it’s doing.

VoiGAS

@raven This is also my experience. But today I watched a spanish YouTube video analyzing Zonesense. They say if you correctly calibrate Zonesense, then it also works during runs. Slower and just three zones, but zone based training should bring better results.
They say (per sport do):
Once : 10 minute warm up, then intervalls > 5 Minutes covering all zones
Every Training: 10 minute Warmup as you described
After this you should trust Zonesense. So if its not red, you are not pushing enough

Maybe I try it…

https://youtu.be/Hy0Ss4-dwoE?is=aBRS4mcrZrPqtUKM

atoponce

@raven

Because it’s a lagging indicator, interval sessions sometimes don’t even register. A track workout of 400m sprints, with 400m walks may or may not register; 100m sprints almost certainly will not.

Suunto has stated that it needs at least 3 minutes before the data stabilizes.

atoponce

@VoiGAS It’s also been problematic for me. I was hoping it would be a good proxy for lactate threshold testing, but that doesn’t appear to be the case. For my workouts, I do Norwegian style sub-threshold intervals of:

10×3:00 @ ~12K effort
5×6:00 @ ~HM effort
3×10:00 @ ~30K effort

I’ve got my efforts dialed in fairly well based on a long history of racing, so I’m confident if I were to lactate test, I would not be surprised by the results. But when I look at the ZoneSense data, sometimes it shows a V̇O₂ max response, sometimes it doesn’t. Even though the paces aren’t changing.

I’m willing to give some grace for heat, fatigue, niggles, and other things, but the data varies too wildly to make any type of reliable or consistent decisions. Sometimes it claims my AnT is around 160 bpm, sometimes 140 bpm. I honestly am not sure how I’m supposed to interpret that.

I want it to work, as it would be great validating how I’m training, but I’m not sure how to interpret the frequent large day-to-day and within-workout swings.