How accurate is HRV?

[SunsetRunner]

How accurate is the HRV in the health metrics?

Moderator edit: updated subject for clarity

[SallyOz]

@t.parker Sounds like this really is part of your profession. My expertise was initially in zoology and later in information technology. The Fitbit is to help me keep moving when data keeps me at my keyboard for too many hours! The HRV and VO2max became shiny things that I just had to explore. I love finding things that are unknown to me. I have a lay-persons interest, and you are quite right about feeling good about the fact that you get good 'marks' against whatever dataset the purveyor of the product has decided will most likely get you to spend your money. It's right back at elementary school where the competitive gene kicks in and we all want good report cards. As an older person I just want to keep away from doctors and medication. I have just read an interesting book called "The Myth of Normal" and the statistics on the number of people ingesting chemicals in the name of 'medicine' is quite alarming. I wont be pushing myself to perspire anytime soon. Taking my daily HRV is a bit like a canary in a coal mine ... hopefully I'll get a clue if something is awry. I've left it way too late to add athlete to my CV. 🙂 

[JamoC]

Cool - make sure your H10 always has a semi-fresh 2025 batt when you use the ECG or eHRV type apps. If the batt is lower than 50%, the readings are trash. 

[nearthound]

So glad I found this thread. My FitBit Charge 5 tells me Cardio Fitness is 37 to 41 which is "excellent for women (my) age". I'm 75. But my HRV ranges from 10 to 21....which has had me kind of concerned. I guess I should look into an ECG grade chest strap heart monitor, huh?

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I also was unable to post bc I kept getting notifications I had forbidden numbers in my text. I figured I'd type "to" instead of a hyphen...and I was able to post my numbers. Quirky.

[Shelly0872]

Same here

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[AngelaAngell]

Same, mine stays in the 20s.

[SunsetRunner]

It can’t be accurate otherwise I’d be dead for sure 🤣

[Shelly0872]

Me too ….. stay strong stay fit

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[nearthound]

Re "The Charge 5 jumps from a lowest of 8 to a highest of 32 with the majority clustering between 14 and 22. The H10 has a low of 48 with a high of 60 and clusters between 54 and 56. So no correlation at all."

Do the numbers of C5 and H10 move in the same direction/in sync?

[nearthound]

Found some articles that may help explain issues re measuring HRV via wrist/hand arm vs directly from heart. 1) "Most watches, armbands, and fitness heart rate trackers are designed for heart rate only. This means that they do not accurately measure R-R intervals. R-R intervals are the exact time measurement in milliseconds between each heartbeat that are needed for truly accurate Heart Rate Variability (HRV) calculations. These millisecond times between each beat are also called IBIs or inter-beat intervals....There is no affordable hardware or sensor on the market that can measure accurate HRV from the wrist, arm, or hand using optical sensors or PPG while you are moving. You must remain still (within reason) to accurately measure HRV using that technology in those locations on the body...In the meantime, the best option is to invest in a chest strao heart rate monitor or an HRV-specific device like the CorSense. These devices are built for accuracy first and specifically for Heart Rate Variability." https://help.elitehrv.com/article/119-why-can-t-i-use-my-wrist-hr-monitor-or-led-pulse-oximetry-moni...

"The optical heart rate measurement (via arm/wrist/hand) is based on photoplethysmography (PPG), whereas the heart rate sensor with a chest strap measures (directly) the electrical activity of your heart."  

https://support.polar.com/en/support/what_are_the_pros_and_cons_of_wrist_based_heart_rate_measuremen....

3) "The limitations of PPG technology are significant. PPG is accurate for measuring HRV in healthy individuals who are at rest, but quickly loses accuracy when any physical activity is introduced. Furthermore, PPG technology is more likely to be missing data. This is because PPG sensors require a relatively long settling time due to the need for cancelling the effects of ambient light, accommodating different skin conditions and colors, and dealing with motion artifacts."

https://blog.getlief.com/how-to-measure-heart-rate-variability-ecg-vs-ppg/

[eltoo]

I just started receiving FB HRV data showing my HRV at 15, which seems quite low and I'm relatively fit with a RHR of 60 and a FB cardio fitness scor of 53.  This made me both anxious but even more, curious.  After some online research and reading other Fitbit community chats, I downloaded the "Elite HRV" app, which utilizes a polar HR strap to measure HRV, via bluetooth.  I got a reading of 52 on the first try.  There seems to be a view that a chest strap provides more accurate HRV information vs a wrist-based monitor, but I don't know if that's true.

More importantly, the Elite HRV site has numerous articles with useful background on HRV.  One of them has this table below, which indicates that there are multiple HRV software programs that use different metrics to report user HRV (their app metric is the 3rd column).  I don't understand why there are so many different metrics for measuring the same thing.  It's also not clear to me what metric Fitbit is using to report HRV and how it compares to these other metrics.  

I just started using Elite HRV but you could try that to see if it is useful for you.

[t.parker]

@eltoo The optical sensors are unable to detect RR intervals (for that you need ECG equipment, H10 does that). Instead, they detect PP intervals. That shouldn't matter as the sinus rhythm RR and PP intervals are the same. However, the measuring method with an optical sensor that may have not been designed for it (for example, not high enough sampling frequency) may affect the accuracy and more aggressive error correction may have to be put in place. That may result in smoothing out the data and lower overall results within the specified time domain. It doesn't mean it's inaccurate. It's just at a lower resolution.

In here I posted an analysis of a month of data between Garmin and Fitbit optical HRV (night). The difference between both readings may be a result of two things - methodology (a table you posted shows how it may affect the final result) and time domain. Since we are talking about sleep HRV, the time domain may be slightly different (depends when the sleep is detected on both devices) and a method used to obtain a result. But overall, the trend of both readings matches quite well (and if I get the data from last month and a longer period I observe visual matching of the overall trend). People focus too much on a single number without much knowledge of how it is being calculated, how sensor errors affect the results etc. For me, two different devices provide different absolute results, yet very similar relative results. Whether this indicates accuracy? Scientifically, on some level, yes. Mind that EliteHRV isn't made for all-night HRV measuring (and they explicitly say that, although it is possible to do, I never tried).

Answering your last question, the reason why there are multiple metrics (companies like to call them "scores") is to bind you to a particular solution. Most of them offset some paid subscriptions for more in-depth analysis (EliteHRV does). Having proprietary metrics prevents users from migrating.

[nearthound]

Excellent! Chart is very interesting. Had been wondering about whether the HRV #'s on FitBit vs other devices might correspond. Have googled, unsuccessfully so far, for similar chart comparing a FitBit and an ECG grade chest strap. Will continue to search.

[Shelly0872]

DONT PAY ANY ATTENTION TO THE HRV ON FITBIT

NOT ACCURATE!!!!!!!

Download a heart app and check it there 💪👍

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[NKroeger]

How do I get to that download?

[Shelly0872]

It’s called Welltory has a red heart ♥️ it’s shows your HRV

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[NKroeger]

Thank you’

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[eltoo]

Elite HRV - free app.  Requires a chest strap (e.g. Polar) to measure HR and HRV.

[BellaCat]

I’m so glad to have found this thread! I wear an Inspire HR. Last week FitBit added the HRV metrics to my dashboard. I didn’t know what HRV was and when I looked it up, I felt on the edge of a panic  attack, thinking I was going to die in my sleep with a score of 27! I am somewhat relieved to see so many others with similar scores and to learn this isn’t necessarily  an accurate metric. But I am going to bring it up with my doctor next week, just to be sure. 

[hannakopo]

Holy crap I have never been more relieved to find a thread online… Mine keeps reading at 25 and here I am thinking I am literally dying. Why the heck has Fitbit not fixed this or at least taken it away if it’s this inaccurate!!

[SunsetRunner]

Haha! I know right. Mine at its highest has been 49 and lowest 27! I’m a
fitness instructor and I go mountaineering. I couldn’t be more cardio fit
🤷‍:female_sign: