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A few months back I upgraded my trusty fenix watch for a newer model, so I now have loads of new metrics to play with. One that Garmin seem to use a lot for calculating things like sleep score, recovery, stress etc is HRV.
Now, looking online I see that overnight HRV is supposed to generally increase as you recover. There are ups and downs of course but generally the trend is supposed to be upwards. But I’m finding the opposite. I drop off fairly easily and HRV quickly climbs to the 70s. But then drops (often below 20) around 2am and is low for a few hours before creeping up to around 40 odd just before the alarm goes off. I know that the numbers themselves don’t mean much but I wonder if the fact that it has more of a bathtub shape contributes to the generally low sleep scores the watch gives me?
Sleep scores are shit. Literally not worth paying the slightest bit of attention to.
The only metric that matters is how well you feel that you slept.
I'm not convinced it's telling me anything useful. I've had terrible nights where it's recorded a great HRV score, and vice-versa.
I suspect that if you wore two watches you'd get two completely different measurements of HRV.
Actually the score does seem to correlate pretty well with how I slept. The possible exception is after a hard effort where I may feel that I’ve slept well but the watch thinks I haven’t recovered that well. Other than that I’d say it’s pretty spot on and even there it may be doing a better job of judging my recovery than I do based on my previous record of injuries 🙂
Sleep stages do seem to be rubbish, but the overall score (based on “stress” as measured by HRV) seems ok I’d say.
That timeline is more what I’d expect to see and I’m guessing with those numbers you may be a bit younger than me (very late 50s). The two watch thing might be interesting. HRV shouldn’t be that variable between devices really as it’s just measuring the variability in the beat to beat interval.
It's not useful, because the more you attempt to improve it, the less likely you are to.
How so? Do you mean that worrying about how you are sleeping won’t help you sleep? In which case I’d agree. But there are plenty of things from mindfulness to medication that have been shown to improve sleep (and HRV). But I’m not so much interested in whether HRV is a useful number (there is plenty online and in published literature about that) more whether the trend in HRV overnight says anything useful. I’m going to put you in the No camp for that one Kramer 🙂
How so? Do you mean that worrying about how you are sleeping won’t help you sleep? In which case I’d agree.
That's exactly what I mean. Sleep is the very definition of a passive activity. By focusing our attention on it, through for example smart watches that give us a score, it interferes with that passivity, and often makes things worse, not better.
Sleep is something that should just happen. Trying to improve it makes it tend to not "just happen".
Get up at the same time every day.
Go to bed when you feel tired in the evening.
If you feel that you've woken a few times in the night, try staying up a bit later.
If you've slept all the way through and only been woken up by the alarm every morning, try going to bed a bit earlier.
I'm a GP with an interest in sleep. I'm also developing a sleep app.
but I wonder if the fact that it has more of a bathtub shape contributes to the generally low sleep scores the watch gives me?
Yes low hrv (as opposed to the bathtub shape) will tend to show as low sleep scores (as its considered stress).
I do find the sleep scores relatively accurate eg when I have an appalling nights sleep it does show up. How useful that is though when I am feeling thickheaded anyway is questionable.
As such dont pay much attention to it. HRV I do find semiuseful as a general trend eg if it drops unexpectedly (eg not training hard and not a beer or two) I have found it to indicate a bug is kicking in. Also if its staying low I would tend to refrain from training heavily. Again though my body mostly is giving unsubtle hints along those lines anyway.
All the evidence is that sleep tracking is bad for sleep.
I've been using HRV4Training for yonks. It doesn't score sleep just gives me HRV and resting heart rate when I use it in the morning before getting up.
Resting heart rate seems to track pretty well with fatigue, illness, alcohol abuse but HRV may as well be some randomly generated value. It doesn't appear to correlate with anything.
I only use HRV as one factor to determine whether I'm overtraining. It does seem to fall to "unbalanced' (on the low side) when I'm overdoing it (and can feel I'm overdoing it) it does ecover when I back off or after rest days
There is a pretty big range for balanced from low 60s to low 80s average overnight - anything within that is scored as balanced. It's only a broad measure to reflect a trend over time and variance outside that which may be indicative of an issue and in sport context whether to adjust training load
I've only ever been classified as "low" after a night on the piss
This is using a Fenix
My take (but Polar not Garmin) is that sleep scores are an aggregate of a number of parameters, of which HRV is just one.
I use the sleep score as a guide to overall trends, and know what impacts it (red meat, too much booze, work stress, late nights.... no sh1t sherlock) and can make some changes to improve it.
HRV I tend to keep an eye on the night average rather than changes during the night, and then keep an eye on trends over days and weeks to see if it's changing.
I only use HRV as one factor to determine whether I’m overtraining. It does seem to fall to “unbalanced’ (on the low side) when I’m overdoing it (and can feel I’m overdoing it) it does ecover when I back off or after rest days
Pretty much the same as me. Mine ranges from low 30s to high 50s though,
@kramer you’ve got the worry of a shifter rebuild keeping you awake until the weekend!
@Kramer; I think I understand what you are saying and wouldn’t disagree in general, but I don’t think there is a problem with the numbers, it’s what people do with them that can be an issue. I don’t see a problem with a watch saying “you might think you recovered from that hard session, but your numbers aren’t back to their normal range yet so maybe take it a bit easier today”. It’s certainly helped me get away from my previous “go hard until something breaks” approach to training and I’m getting fewer injuries. Some people have also reported that drops in HRV detected that they were coming down with something before they got symptoms, so they could adjust their training accordingly. But if you are laying awake at 3am worrying that your HRV is 37 when you think it should be 42 then maybe you shouldn’t be wearing your watch to bed. It’s a fitness/lifestyle tracker not a medical device, but it can give useful advice to support training and nudge people to make positive changes if used properly.
Personally I don’t have a problem with sleep but I am a numbers geek and like to understand how the algorithms work. So I was interested to see that the shape of my overnight HRV curve was different to what Garmin (or firstbeat) thought was “normal”. I wouldn’t set much store by a number but a consistent pattern probably indicates something so I thought I’d see if anybody else had seen this. My hunch is that the “normal” curve that Garmin expect is probably derived from a small sample of mostly young fit folk and the curve may well be different for older folk (who tend to wake earlier naturally). Or it could just be that my curve has always been like this but I’ve not had a way to measure it before. As I say, I’m not bothered by it, just interested.
Anyway, good luck with the app. I know some GPs up here have reported some of their patients having some success with sleepio but not sure what that involves. The idea of using an app to help sleep seems a bit strange given that one of the first bits of advice seems to be to stay off the screens in the evening, but it sounds as though they can be helpful and it’s got to be better than chucking sleeping pills or anti-depressants at people who don’t need them.
@susepic; yes I think they do use a number of factors to make up the sleep score and won’t say exactly what as that’s their commercial advantage. I think Garmin probably factor in the time spent in different stages too. I don’t think any wearable measures stages accurately though which makes the sleep score rather dubious. That’s why I prefer HRV. It’s a simple metric rather than a combination of factors and has been shown to correlate with useful things. It should be relatively easy to measure too so the accuracy shouldn’t be too awful. I wouldn’t pay much attention to any number but as you say, trends over time can be useful.
@scotroutes; HRV seems to vary a lot from person to person (and hugely during the day). It also declines with age. There is a graph of normal ranges online somewhere but I think 30-50 would be on the high side of normal for someone in their 60s but on the low side for someone in their 30s, for example. As you say though, if it is useful at all it is in terms of changes compared with your normal and trends over hours/days rather than the number itself or any individual measurement.
I use the ithlete app - with a chest strap HRM - to measure HRV daily first thing in the morning and find it - along with RHR - a useful steer on recovery state and, occasionally, early warning of illness/infection. I'm hardly an HRV expert, but what I do know is that sometimes it does odd things - eg: it can actually rise when your immune system is activated, though not always - and that it's very much an individual metric and absolute values aren't comparable between individuals, you're more looking at trends than individual values.
Fwiw, ime sleep in the single biggest factor in recovery after exercise intensity and illness.
I'm not sure how useful overnight HRV readings are to you. Or how accurate wrist-mounted HR scores are when it comes to measuring the milliseconds between successive heartbeats. What I'd hope is that Garmin would have found a comprehensible way of summarising that data in a way that a) makes sense and b) is actually useful to you, though I guess that would be very un-Garmin...
Mostly though I would go on how you feel and perform rather than getting too focussed on the micro-details of HRV scores.
Been interesting having a Whoop band on, as i am part of a study of diabetics and performing in sport, so don't pay for it, had COVID last week and it forewarned me it was on way, and then watched my sleep recovery literally drop to 1%, HRV at a third of normal, but it gives metrics like skin temperature which at its worst was up by 3.3 degrees, by blood oxygen dropped 5% and resting heart rate went from averaging 49 bpm to high 60's, and respiratory rate went from averaging around 14 breaths per minute, to 18-19
Made me realise just how tough on the body it is.