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Nov 2020
1:16pm, 22 Nov 2020
6,657 posts
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The_Saint
I will have to look closely at what is going on. I must admit that HRV was something I got really interested in and played around quite a bit with an application called Kubios? What made me lose interest was partly that the data seemed to me to have nothing really to tell me about running and a discussion with a sports physiology PhD student who agreed that it was fascinating "if only we knew really what it is measuring and whether this can be used other than in a wand-waving sense to say more variability is more healthy".
I find the whole stress thing it is used for utterly facile.
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Nov 2020
1:24pm, 22 Nov 2020
32,218 posts
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SPR
For clarity re the 245, I was referring to when using optical. HRV shows up fine with a strap.
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Nov 2020
1:30pm, 22 Nov 2020
6,658 posts
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The_Saint
Yes that is what I understood you to mean
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Nov 2020
4:22pm, 22 Nov 2020
4,030 posts
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StuH
The HRV app I use on my Fenix 5 will measure using optical but it is derived from IBI not R_R intervals? No idea what that means *whoosh*
"OPTICAL Requires IQ 3.0 watch and IQ 3.0x firmware (FR245,645,935/45,F5/F5+, Marq, VA3 )"
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Nov 2020
4:41pm, 22 Nov 2020
13,048 posts
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Badger
Inter-beat interval; it should be the same number, but optical doesn't actually detect the R-wave so it doesn't make sense to call it R-R interval.
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Nov 2020
5:02pm, 22 Nov 2020
801 posts
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Sam Jelfs
So, without going into too much details...
Heart rate is controlled by the Autonomous Nervous System (ANS), which in turn is divided into the Sympathetic and Parasympathetic systems. The sympathetic system is basically the "fight or flight" responses, while the parasympathetic is the "rest and digest", so they are working against each other. Sympathetic system raisies your HR, parasympathetic lowers it.
In a normal healthy person these two systems are roughly in balance, so the slight changes in which one is dominant at any one time leads to slight variance in your HR, and hence heart rate variability. Think kids on a see-saw, they are in balance and just varying up and down slightly.
Now the issue is that in say a stressed person, one system becomes dominant, and in turn the HRV decreases, but many things affect this balance of the two systems, so being able to say why the HRV has changed, thats the tricky part. It is a correlate of short term stress, so it can be useful, in the right context.
Interestingly there are other responses, such as spikes in electrodermal activity that can also be linked with stress, in theory.
Now, the issue with HRV and Optical Heart Rates...
Unlike in an ECG where, hopefully, you have a nicely defined R-peak, it can be hard to reliably extract the same part of the signal every time.
The peak isn't a nice sharp peak like it is in an ECG signal, but really it's quite a smooth crest.
Most OHR, especially ones in watches, run at quite a low sample rate, 120 Hz or around there. That means that each sample represents 8 ms in time, you only have to be off by a couple of samples to get your HRV wrong.
For measuring purely heart rate, well thats less of an issue. You find the peaks, calculate the time between them (the InterBeat Interval, or IBI), average across say 30 peaks, and your good. Maybe you are a few ms off on the first IBI, no issue, it will average out on the next one.
Now there are ways around it, and techniques you can use to more reliably extract the IBI, and therefore HRV, but that starts to get into more signal processing theory than we need right now...
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Nov 2020
6:59pm, 22 Nov 2020
19,564 posts
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flanker
Garmin must have reasonable faith in there processing algorithms as (I think - from memory, from a while ago) they incorporate it into the first beat stuff and the dynamic training plans?
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Nov 2020
7:13pm, 22 Nov 2020
803 posts
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Sam Jelfs
The original Garmin sensor and algorithms were made by Philips, so of course they are good 
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Nov 2020
7:17pm, 22 Nov 2020
32,219 posts
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SPR
Are the higher end watches showing HRV on Runalyze via optical?
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Nov 2020
7:38pm, 22 Nov 2020
72,090 posts
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Gobi
I have HRV on the Fenix 6 but what is Run analyze
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