Suunto ZoneSense
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@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.
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@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.
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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!
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@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.
Vector/T6c/Ambit 3 Peak/S5 Copper/S3/S7 Ti/S9 baro Ti/S9P Ti/S9PP Ti/Vertical Ti/Race Ti/RaceS/Ocean/Wing/Race2Ti
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@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.
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@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.
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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!!!
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@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.
curious to know why, with the same HR source, the SV and SR results differ.
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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.
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@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.
