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HRV measurement inconsistency

I'm confused about the results I'm getting and I'm not sure if this indicates a problem with the system. I have been taking multiple readings most mornings to see how consistent the results are and to see what changes in my position/breathing/etc.. do.

In general I see relatively consistent readings but not enough to have confidence in the results. 

For instance, this morning I woke up, walked to the kitchen to wet the chest strap, put on the chest strap and laid back down. I then waited about 5 minutes and took my HRV a number of times without moving more than my hand. Here are the results I got:

07:05 - 76.0

07:09 - 77.6

07:14 - 72.6

07:19 - 73.1

07:22 - 76.5

Those are without me moving at all. That level of inconsistency really doesn't give me confidence that any particular measurement is meaningful.

This isn't uncommon. Yesterday I had the same routine and got these:

08:22 - 85.6

08:25 - 81.6

08:29 - 78.0

Is there something wrong with the device? Why are my results all over the place and how can I trust the results if the app just bases the readiness on the first reading of the day?

Since no one else responded I'll give my 2cents worth...the HRV reading will vary based on your stressors, e.g., as you laid there were you thinking about work, the day ahead, your neighbor who plays their stereo too loud last night, etc.  Even being awake for a while longer will change your HRV so I do not think your device is faulty.  Your readings are normal for that period.


Tom thanks for replying, I'm a little disappointed no one else has been able to weigh in.

I have trouble believing that my HRV would be that heavily influenced by just my thoughts in the moment. Frankly if it is that makes it significantly less useful. The difference between 85.6 and 78.0 is a big jump and seeing as I'm generally letting my mind drift and moving in and out of dozing while I'm doing this I doubt it's my mental state.

My numbers from the last couple days have been more consistent but I'm not sure that's better or worse.

For the price of the software (since that's mostly what we are buying) I'd like a better understanding of what's happening and which readings to trust.

Did you get the HRV Manual as part of your package?  It does have quite a bit in there to explain HRV and how it can vary.  There is also more HRV information online if you do a search for it (I'm sure you have but it essentially says the same thing...stressors will affect your HRV.)  You should trust your first reading of the day if you take it at the same time and in the same position.  You will begin to see a pattern in your readings so that eventually you can see the trend or stress-recovery from work outs and stressful days from work and travel.  In the same vein your HRV will reflect how faithful you were to your recovery protocols.  I was made a believer in the HRV and software when my HRV reading was incredibly low one morning and by noon of that day I had a mild case of the flu.  Felt fine when I woke up but my CNS knew otherwise.  I also think having this technology available for what it cost is very reasonable considering what overtraining or undertraining can do to one.

I have the book and have read online. I'll review it again. I'm hoping to see some pattern but at this point it isn't giving me anything beyond what I get from standard training patterns. 

I'm waiting to see how useful it is as I ramp my current training regimen to a level where overtraining is a more serious risk.

TK - how many weeks/ months have you been taking readings? And what is the average HRV reading from it over that time period? 

I do shift work and can't take HRV readings at the same time everyday.

I'm finding the pattern of readiness over the weeks and month have given me more useful feedback than the single reading for the day...



The standard repeatability of HRV, including any HRV system, is about +/- 2 points. This is exactly the same thing you'd see if you were measuring heart rate, blood pressure, etc. and even when you measure hormonal function, you'll always see variation from one minute to the next.

This is simply how the body works, it's very dynamic and HRV in particular is very sensitive obviously to sympathetic function, which can be fairly heavily influenced through your thoughts, which is biologically designed that way for a reason. You can very easily elevate your heart rate 5-10bpm or more simply by thinking about something that makes you anxious, for example.

When you do this, you're not just elevating heart rate but an entire cascade of hormones tied to the stress response. Go read the book Why Zebras Don't Get Ulcers to understand just how all this works, just thinking about things in a certain is a major factor in a whole host of diseases so yes, your thoughts can certainly influence your HRV.

This is why it's generally best to simply take the measurement once, it will invariably provide the most accurate gauge. Looking at your example, this is clearly the case as your first or second measurement was highest and then you simply got anxious from laying there over and over again taking the measurement. That's normal and it simply reflects how the body works, not that it's inaccurate by any means, it's simply a reflection of how the body's autonomic function works.

In any event, take it once, hit "save" and your results will be accurate.


I think we have to remember that, although we have paid a lot for this service, we are aiding the pioneers of this technology in debugging and perfecting their innovation. There will be bugs, and there will be problems; this is the expectation one should have when supporting and believing in any new technology.


That being said, In my opinion, a 10% variance between you lying in bed (and getting fairly consistent concirrent results), and getting up and walking around (stimulating yourself, and modifying breathing patterns), is expected. The fact you get consistent results minutes by minute when taking the readings is proof that is technology is VERY reliable. The error in your perception, is that you were measuring two different states in your morning (lying in bed immediately after waking, and then lying down after becoming fully alert, and going about your morning routine), not one.


Thanks for the support, but let me make it clear that the numbers being discussed are not the result of bugs or problems, it's simply how HRV works because it's how the body works. It's dynamic and as HRV is a very sensitive measure, the repeatability is +/-2 points in a standardized setting no matter how long the system has been around. HRV as a technology has also been around since the 1950s and 60s, I wouldn't exactly call it new, it's simply a new application of it, but any HRV system would show the exact same variance regardless.

The only way to change this would be to take HRV readings for much longer periods of time, 30-60 minutes, but obviously that's impractical. HRV is measuring rather small inputs in changes to autonomic function, a fundamental system to maintaining homeostasis and life, so given this, it's to be expected that it's a fluid system that's open to change through a range of activities, including psychological events. In the end, as long as the test is performed as described in the book/videos, then it will provide consistently accurate, reliable and valid information.


Interesting; thanks, Joel.

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