Looking for a Rabbit Hole :) (HRV)

Good Morning,

I am looking for a Rabbit Hole and figured this was the perfect place :slight_smile: - I want to learn and explore more about HRV, the Apple Watch and overall health, but especially the connection to the autonomic nervous system and the connection to mental and physical fitness.

Tons of apps out there but I am looking for some insight from the folks here - especially links to some scientific papers or research based articles.

Thanks !

Commenting because I too would love to learn about HRV, but I’ve not found anything simple enough for me to understand.

@geoffaire - Here is a start - with some decent links to science based articles. Heart Rate Variability (HRV) as a digital biomarker for Mental Health and the promise of Apple Watch - MyHealthyApple

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I found Whoop had the best info on it.

It’s interesting you mention it because my Garmin watch started doing HRV this summer and I found it interesting. Drink? It goes down. Illness coming? It goes down. Etc. I started to learn what has an effect on it and what my normal readings were. Then October came and my HRV plummeted. I figured I was getting sick or I was overdoing it. I took a few day break, no illness appeared, and it was still low. It stayed low all of October and then started to come up again. Was normal for a week and is now going down again.

My watch is telling me to take a break (which I am because I pulled a muscle), so it’s not that. So now I am curious if there is something bigger going on, but I have no idea what to do about it. I figure my doctor would laugh at me unless I had something more concrete. On the other hand, I do have some heart issues that are known and it makes me wonder if I should talk to my cardiologist.

Anyway, I have read a few articles on it and I sort of understand what it is telling me and how it works, but I am also to the point that how it works doesn’t really matter to me. I know if it’s low something is going on, but I have zero idea of how to fix it short of not getting drunk or sick.

I’m curious what your HRV would report when you exercised. Would exercise push you from chronically to extremely low, and then it would crawl back up to chronically low? Or would it show roughly the same number after exercise?

I went through a period like this and I actually did have a health problem. I was able to return to normal readings after three months. Hope you are healthy and it’s a miscalibration.

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I really don’t know, but there seems to be so many factors that can affect it, I am not sure how you would be able to say for sure. From some of the stuff I have read, people shouldn’t really worry about it, and this is just something that companies are trying to market to make money (see Whoop). On the other hand, it clearly showing something happening.

During exercise, it goes low and stay here. This is my HRV during a run. It doesn’t really tell you anything.

Edit: And another thing (sorry, I think and read about this stuff a lot), every device is recording this differently. Some are using different types of HRV, others are measuring it more or less. I think Whoop uses a different HRV than Garmin. Garmin is mainly going off of measurements from sleep, while Whoop is all the time. Then I believe Apple Watch only does it when you meditate and takes a couple of readings during sleep. Elite HRV is just telling you to take readings in the morning and evening. It’s really all over the place.

A few years ago, I was considering using HRV in a research project, and so I did a quick search in Devonthink to find any articles I might’ve saved. This open-access article might be a good place to start: Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research – Recommendations for Experiment Planning, Data Analysis, and Data Reporting

The Apple Watch has probably come a long way in the time since, but at the time, I found Biostrap to be a good consumer-level product for obtaining clinically valid HRV. You might add the word “biofeedback” into your HRV searches to get more relevant info/articles.

At a very basic level, here’s my understanding of how to think about HRV. HRV is a measurement of how consistently the heart beats. If it beats very consistently (:anatomical_heart: - :anatomical_heart: - :anatomical_heart: - :anatomical_heart: think a metronome), the variability is low. If the heart beats inconsistently :anatomical_heart::anatomical_heart: - :anatomical_heart: - :anatomical_heart::anatomical_heart::anatomical_heart: - :anatomical_heart::anatomical_heart: - :anatomical_heart:, the variability is high. As far as I know, we don’t fully understand the causes or implications of low vs high HRV. Sleep and many other factors affect HRV.

There are theories that attribute a low HRV to the autonomic nervous system responses, but the jury is out on whether they are valid. You might look into Poly Vagal Theory and also search for its critics. Here’s one article I found quickly: Toward understanding respiratory sinus arrhythmia: Relations to cardiac vagal tone, evolution and biobehavioral functions.

Neat question! I’ll be following to see what others have learned.


IANAD, but I’d reach out to mine with a quick note if I were you. You can even start it with, “I imagine you’ll laugh at me because all I have is my Apple Watch data to go on, but I noticed this and wanted to mention it in case it’s meaningful to you.”


+1 on this @Leeabe51 better to check than not.

IAAD and at best this is investigational.

If a patient has other cardiac symptoms/issues, then your doc will proceed with a workup based on those.

If you are otherwise healthy without symptoms or signs of cardiac disease, your doc will politely smile and move on.

When considering the use of any general purpose fitness device for health screening rather than simply for fitness, it is really helpful to do some reading on the concept of Bayesian analysis as it applies to screening tests. If you study a healthy population using a screening tool of low specificity, then you have a high risk of false positive findings. The harm from further testing to follow-up those false positive findings often exceeds any benefit of the screening - both in the sense of medical harm and economic harm.


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This is great stuff… Thank you all. I definitely found my rabbit hole!

Although this is a heart measurement - my understanding is that it really is giving us information about our autonomic nervous system and it’s an indicator that there’s some level of stress that the body is responding too.


And while it’s interesting to play with on your iPhone, IMHO the likelihood of yielding useful, actionable medical diagnostic or treatment info from this is nil.

Maybe at best it can give you input regarding your general level of stress similar to biofeedback. Interesting but not likely to be actionable information.

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