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Re: Help me understand HRV [lightheir] [ In reply to ]
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I have a polar, which have tended to be the class leaders in HRM sensors.

In general, it tracks with how I feel. Yes, there are outliers which i mentioned in my other post, but yeah, the trends make sense. That's the problem though. It has never told me something I wasn't able to figure out by sitting in bed for a minute and checking in with myself. There's nothing actionable about the information in my opinion. That's great that you enjoy it though.
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Re: Help me understand HRV [imswimmer328] [ In reply to ]
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imswimmer328 wrote:
I have a polar, which have tended to be the class leaders in HRM sensors.

In general, it tracks with how I feel. Yes, there are outliers which i mentioned in my other post, but yeah, the trends make sense. That's the problem though. It has never told me something I wasn't able to figure out by sitting in bed for a minute and checking in with myself. There's nothing actionable about the information in my opinion. That's great that you enjoy it though.

I suspect there's a difference between the new sensor on the garmin's and 'just another HRM. I've used like so many kinds of HRMs in the past (Polar included) - they worked great for straight HR sensing, but they weren't designed with continuous HRV monitoring overnight in mind. Polar has made HRMs for a long time but I haven't seen anything from Polar re:HRV optimization (I could be wrong about this though, I don't research Polar closely.)
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Re: Help me understand HRV [lightheir] [ In reply to ]
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lightheir wrote:
imswimmer328 wrote:
I can't say I've tried to be super scientific about how I take my measurements, but I'll agree with previous posters that I don't find much useful information from it. Didn't sleep well that night, don't feel awesome in the morning, yup hrv says I'm tired. Doesn't actually mean I can't perform that day though. Also had a surprising number of times it says I'm tired yet I had a fantastic night's sleep and I crush whatever I'm doing the next day. Also had it say I'm super recovered after a terrible night's sleep and I perform badly. All in all, yeah not worth the effort IMO.


Again, I suspect the measurement device is at fault. You can't make a conclusion about it properly if you don't have a device or even a protocol that can at first seem validated on obvious states of conditions.

Try again in the future if you get a current-gen Garmin with the upgraded optical HRM sensor (I think all the ones from this year on have it) - it's a huge upgrade from prior models. There may be some methodology in Garmin's algos as well that are baked in - but whatever it is, it's quite good (to my amazement) in my hands. I really thought it would either suck, or at give me some really off results, but my results from the last 2 months including 2 abnormally high training weeks and even the abnormally high training days, get reflected in the HRV that evening.

I don't really need a device to tell me I'm tired after a big session or block of training. What its key intended use though is for people to back off their training when HRV is showing they are fatigued.

To do this though irrespective of how you feel would take immense discipline. Can't imagine many would choose to have an easy day because of a HRV number if they are otherwise feeling great...

What I have seen though is my resting HR (not HRV) definitely spikes if I'm about to get sick. A few times I've had a illness and looking back at my HR you can see a spike leading up to the symptoms presenting. For this reason resting HR is a better metric for me than HRV.
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Re: Help me understand HRV [lightheir] [ In reply to ]
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I don't think you understand what hrv is. Garmin has no algorithm for measuring hrv. That's very well defined, as the root mean square of successive differences (r-r intervals). You simply take each rr square them and sum all up and take the square root. Nothing magic.

The algorithm and sensor technology is all about finding the pulse wave, and finding the "peak" in the pulse wave (measured as change in reflectance of a specific wavelength of light). The pulse wave is much more "rounded" than the electrical pulses measured by chest straps and ecg. As such, peak detection is a bit more tricky (and susceptible to error). In addition, they need methods for filtering out normal variation from watch movement, etc. In some cases they may have to discard invalid samples, and again the "trick" comes in deciding what to discard, and what to replace it with (nothing? Average of prev and next sample? Etc).

All of this is about minimizing the effects of erroneous measurements. Electrical systems suffer almost none of these issues, as they are much much smaller in magnitude and impact. As a result, bluetooth straps to phone apps can just use the rmssd formula above. Most of these systems don't even bother to handle dropped samples. They just report if it apps to any significant measure and say "try again".
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Re: Help me understand HRV [Tom_hampton] [ In reply to ]
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Tom_hampton wrote:
I don't think you understand what hrv is. Garmin has no algorithm for measuring hrv. That's very well defined, as the root mean square of successive differences (r-r intervals). You simply take each rr square them and sum all up and take the square root. Nothing magic.

The algorithm and sensor technology is all about finding the pulse wave, and finding the "peak" in the pulse wave (measured as change in reflectance of a specific wavelength of light). The pulse wave is much more "rounded" than the electrical pulses measured by chest straps and ecg. As such, peak detection is a bit more tricky (and susceptible to error). In addition, they need methods for filtering out normal variation from watch movement, etc. In some cases they may have to discard invalid samples, and again the "trick" comes in deciding what to discard, and what to replace it with (nothing? Average of prev and next sample? Etc).

All of this is about minimizing the effects of erroneous measurements. Electrical systems suffer almost none of these issues, as they are much much smaller in magnitude and impact. As a result, bluetooth straps to phone apps can just use the rmssd formula above. Most of these systems don't even bother to handle dropped samples. They just report if it apps to any significant measure and say "try again".


I'll take your word for it; I'm sure Garmin does have some sensor-specific things they've done like you mentioned to try and get the optical sensor to more closely match an electric signal.

But whatever it is, it's working extremely well for me thus far. I find it hard to believe it's all just garbage and noise like you and others claim, as I havent had a single day yet where it's gone opposite of what my training load and sensation of readiness has been (which is amazing to me, as I've said several times.) If it's work so well for me with the current-gen device, it's hard for me to believe it's giving useless data for others if they were using a similar device.

Even this week, which is my pullback week, eveyr single overnight average has increased from 70ms (low for me) all the way up to 104ms today (normal). The 7-day average is still slightly low, but will be essentially back to normal by the end of the week. I now trust my own data enough to be actionable, which is crucial as well - my HRV was still in the low 80s last night, so even though I had the time, I didn't do my typical doubled swim then bike or run, and just did the single workout, but I'll go back to doubles instead today with the normal HRV. (I did feel more fatigued yesterday than today particularly in the AM, but by the end of the day I felt like I should be rolling!)

My last 3 months of data haven't had a single glitched week where there was a mismatch between my training load/feel vs the HRV, meaning no weeks (I can't even note a single day really) where HRV said "you're tired, rest!" but my fatigue said "nope feel great!" or vice versa. It's remarkable how my curves dip with the big training weeks and then come right back up to green as I decrease load.
Last edited by: lightheir: Apr 5, 23 4:09
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Re: Help me understand HRV [lightheir] [ In reply to ]
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If you want to try and get the best out of the HRV data, you need to sleep with a strap. I don't think the optical sensor is sensitive enough to provide sufficiently nuanced results. That said I do wear my 955 24/7 and look at HRV. I've found it's good at indicating "stress" or sickness but the number in and of itself isn't super meaningful.

-Of course it's 'effing hard, it's IRONMAN!
Team ZOOT
ZOOT, QR, Garmin, HED Wheels, Zealios, FormSwim, Precision Hydration, Rudy Project
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Re: Help me understand HRV [Bryancd] [ In reply to ]
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Bryancd wrote:
If you want to try and get the best out of the HRV data, you need to sleep with a strap.


The study I posted above indicates some are quite good when compared with the "gold standard" of lab-grade PSG. In particular the Whoop 3.0 is dead on. Caveat that the Garmin data isn't from the newest generation of Garmin HRV. These graphs are showing the deviation from PSG, so a horizontal line would be perfect agreement.

Edit: Important context with the graph that the Whoop 3.0 was the only device that provided raw R-R intervals. For the rest the study had to use the output of proprietary black box systems. So it's not apples-to-apples, and the underlying sensors may not be primary source of error. E.g. the authors speculate that the Garmin may have done relatively poorly because it was mixing in waking HRV with sleeping.


In separate sections of the same study, they're also fairly good at estimating broad sleep metrics. Less good at identifying specific phases of sleep.



Last edited by: trail: Apr 5, 23 8:02
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Re: Help me understand HRV [trail] [ In reply to ]
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Re: Help me understand HRV [Thomas Gerlach] [ In reply to ]
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Thomas Gerlach wrote:
Interesting. Do you have a link to the original study?

Post 10 in this thread.
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Re: Help me understand HRV [Tom_hampton] [ In reply to ]
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Tom_hampton wrote:
Nevertheless, once I began rolling workout stress on top of baseline there was never any consistency. It was a crap shoot whether any one workout would cause a high or low reading compared to baseline on any given day.

If I feel good and I perform well for the day, but hrv says "whoa buddy... Take it easy" and I feel fine again tomorrow, and can maintain the pattern for weeks/months/years in the face of unstable hrv readings..... Which should I believe? Results or a metric?

for amateurs like us, the stress load of a workout is negligible compared to the stress of getting up at 4am to make a living etc.. so I don't expect to see correlation between workouts and HRV, and seldom do. Exceptions obviously for major races and similar.

If your RPE and self-evaluation is reliable, you don't need HRV. But most of us can't reliably evaluate our stress levels and ability to absorb training. I started with HRV after getting old and becoming unable to do that anymore, found myself repeatedly overreaching and needing weeks to recover. My secret is I'm tired all the time ;-) and the HRV helps me not to overload.
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Re: Help me understand HRV [doug in co] [ In reply to ]
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doug in co wrote:
But most of us can't reliably evaluate our stress levels and ability to absorb training. I started with HRV after getting old and becoming unable to do that anymore,

I'm awful at it. I'm 49, and have been an endurance athlete since age 13-14 on cross-country teams.

I've driven myself into deep, deep holes regularly across every decade. I do not get smarter. I respond great to training and feel awesome after tough races or training weeks. Until I suddenly don't and I'm already at the bottom of a deep well.
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Re: Help me understand HRV [trail] [ In reply to ]
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trail wrote:
I've driven myself into deep, deep holes regularly across every decade. I do not get smarter. I respond great to training and feel awesome after tough races or training weeks. Until I suddenly don't and I'm already at the bottom of a deep well.

oh yes, did that repeatedly as a young man.. then with kids and a job, didn't have time to train enough to get really broken ;-) then getting old, it doesn't take much anymore to fall into the hole..

the HRV as I say does seem to be helpful, it gives me external validation for easy days which otherwise I don't want to take..

"It is a good feeling for old men who have begun to fear failure, any sort of failure, to set a schedule for exercise and stick to it. If an aging man can run a distance of three miles, for instance, he knows that whatever his other failures may be, he is not completely wasted away." Romain Gary, SI interview
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Re: Help me understand HRV [LEBoyd] [ In reply to ]
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Dammit.
You made me check mine.
I’m clinically dead very soon.
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Re: Help me understand HRV [doug in co] [ In reply to ]
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doug in co wrote:

If your RPE and self-evaluation is reliable, you don't need HRV. But most of us can't reliably evaluate our stress levels and ability to absorb training. I started with HRV after getting old and becoming unable to do that anymore, found myself repeatedly overreaching and needing weeks to recover. My secret is I'm tired all the time ;-) and the HRV helps me not to overload.


I agree with the above.

Just these past 8 days, I belatedly found I had a very low-grade virus. Felt really low-energy for 2-3 days despite it being a pullback week, and for the 1st 2 days I was thinking "WTF?" as I know I typically feel really good on pullback weeks after 2 days. I did have a brief cough for a morning, but I didn't even consider it to be significant at the time.

But my HRV continued to not improve during those 2-3 days, and even went down a little on the 2nd day despite me doing very low exercise. On the 3rd day, I decided to just pull the plug and rest, and by then it was very clear that I was under a bug since there was no possible other explanation for my dragginess (good sleep hrs, low to no training).

Started feeling better very quickly, and in the ensuing days, HRV has gone back up to almost-normal. It may not be a perfect metric, but it's something I'm definitely paying attention to now as an additional data point - I'll start to really consider life stressors, illness, or other things, and if my general feeling of malaise and HRV are suggesting I take it easy - I'm not going to gut out the workouts like I've typically done in the past. (Prolonging illness when you do that.)
Last edited by: lightheir: Apr 11, 23 19:04
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Re: Help me understand HRV [lightheir] [ In reply to ]
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Update on my HRV monitoring over the past nearly half year - HRV for me seems to correlate very well with my general fatigue and readiness to absorb training. If I posted pictures of my HRV, it's amazing how well for me it correlates with going into 'the red zone' when I'm pushing my limits in volume and intensity, comes back up to 'strained' when I'm gradually acclimating to it, and recently, has gone nearly in a straight line back into the green 'good' zone after a mild pullback week and adaptation to the higher training load. Per my Garmin HRV graphs, I pushed into the 'red' zone in early March, and it took me until this past pullback week to get back to normal, which seems about right as I ramped up my training in prep for June races.

Subjectively, I think it has a lot of potential value in integrating non-workout stresses, as my whole family got hit with a mild cold for a few days at one point when I was in a pullback week, and even with cutting a few sessions out completely due to excess fatigue and sleepiness (we all had it, with some sniffles), HRV didn't come up and stayed strained.

I still think you have to pay attention though and not just autopilot HRV, as I suspect it's a better measure of 'global' fatigue and not so good for muscle-specific fatigue. So for example, if I went out and did a lot of super hard run sprints that toasted my legs, but was still overall low volume, I suspect my HRV wouldn't go down a lot. At least that's what I think based on when I've done some super hard swim sets that weren't big in volume.
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