A little about HRV

HRV (Heart Rate Variability) is one of the metrics that the Oura ring tracks. I’ve begun to learn a bit about it, and thought I’d share what I’ve learned so far, and then share a small personal observation.

Very briefly, HRV has to do with the variations in the timings between heart beats. If your heart rate is 60 beats per minute then about one second will pass from one heart beat to the next—but only about one second. In actual fact, sometimes it will be a few milliseconds more, and other times it will be a few milliseconds less. Those “more or less” amounts are your heart rate variability or HRV.

Most of what I know about the HRV comes from an interview on Human OS Radio podcast with Phyllis Stein, Director of the Heart Rate Variability Laboratory at the Washington University School of Medicine in St. Louis, called Introduction to Heart Rate Variability (HRV). It’s definitely worth a listen, if you do the podcast thing.

A lot of HRV is related to respiration. I noticed this when I got my first heart rate monitor thirty years ago: Every time I inhaled my heart rate speeded up, and every time I exhaled my heart rate slowed down. This effect is pronounced enough that the Oura ring can calculate your respiration rate just by watching your heart rate speed up and slow down with each breath.

HRV is widely used as an indicator of the balance between your parasympathetic and sympathetic nervous systems: If your parasympathetic nervous system is functioning well you’ll see quite a bit of variation. When it’s not functioning well—for example, when you’re persistently stressed—the amount of variation in your heart rate will decline.

Since I got my Oura ring, I’ve been tracking my HRV, looking to see if this or that bit of self-care practice will increase it, and I’ve noticed one thing that seems kind of interesting: Very often my HRV will be quite low in the first half of the night, and then be higher (and with higher variability in the variations) in the second half of the night. Here are three recent examples:

I speculate that this is related to the fact that I’m still digesting supper at bedtime, or perhaps that alcohol I’ve consumed is not fully metabolized yet. I’ve been hoping that life would produce a natural experiment to test those two theories, but so far haven’t gotten one. (That is, days when supper or cocktail hour were very early or had to be skipped have also been days when some other factor—such as illness, an unusual bedtime, or unusual stress—confounded things such that I couldn’t really draw any conclusion about the effect on my HRV.)

Oura ring warned me

For a week now, the forecast has been that yesterday would be the first really nice day of the season, and I had decided a week ago that I’d go for a long run.

I tried to set everything up for good readiness, with a medium run back on Monday (so it wouldn’t be too long between runs), and then ordinary amounts of walking on Tuesday through Friday.

However, it wasn’t to be. I felt weak and sluggish right from the start, and found that even just maintaining a slow pace required that I ramp up my heart rate as the run went along:

(All that stuff in the yellow is too high, which is basically the whole run. I kept it almost in the green for the first mile, but after that it was way too high the whole time. The tiny bit where it spiked up into the red at the end was when I was sprinting to the button to get a walk signal.)

I have to say that my Oura ring warned me that my readiness was only so-so yesterday:

The main negative contributors, from the Oura ring’s perspective, were a mediocre night’s sleep, and a slightly elevated resting heart rate—and in particular, a resting heart rate that took most of the night even to settle down to that slightly elevated level (the “recovery index” part):

Last night my sleep was much better:

But it didn’t lead to a much higher readiness today, because yesterday’s run, even though it was a pretty feeble effort, was enough to mean that today I should at least somewhat take it easy:

As it happens, I was pretty happy to do that. I got a reasonable amount of movement today, while nevertheless taking it pretty easy. Included in the day’s movement was the first bit of barefoot walking of the season. I also spent just a few minutes punching the heavy bag, mainly to get some photos for an Esperanto blog post on one aspect of my summer training plans.

Oura-ringing out the old year

For a couple of years now, I’ve been having some trouble sleeping. It’s not a constant problem, but it has become more frequent than the rare thing it used to be.

I think the problem is just a string of one-off instances of stress. During this period I had one older relative begin having cognitive difficulties and have to move to a facility that could provide additional care, my cat got sick and eventually died, had some personality clashes related to volunteer work I’m doing grow into a problem that eventually involved lawyers, and had another older relative began showing signs of cognitive difficulties.

Each of these resulted in a pattern where I’d fall asleep just fine, but then wake up in the middle of the night and start ruminating about the issue of the day and be unable to fall back to sleep for an hour or three.

In the past when I had problems of this sort they tended to be short-lived. I’d stress out about something for a night or two or three, but the issue would be resolved soon enough and I go back to sleeping fine.

Here the issues have stacked up, new ones following the old ones.  Further, some of them don’t go away. They linger on.

As I say, I think that’s what’s happening here. Ordinary life stresses have simply come at me a little too hard and a little too fast, with the result that my sleep has been impacted.

However, maybe that’s not all that’s going on. Maybe there’s more to it. I know there are some other issues. For example, if I don’t keep my carb intake down my nasal congestion returns, and that dramatically interferes with my sleep.

Given that I’m not sure what all might be wrong, I thought it might make sense to investigate further—gather some data, and see if I couldn’t find some patterns in my sleep problems. To that end, I bought an Oura ring, a tracking device along the lines of an Apple watch or a Fitbit, but with its focus specifically on gathering and analyzing data about sleep.

I’ve only had it for a week so far, and I’m really just getting started at looking for trends in the data. For example, three nights ago I slept poorly (awake for almost 2.5 hours of the almost 9 hours I was in bed).

One possible reason was a too-large meal too late in the day. (It was the Winfield Village holiday party.) One piece of data that suggests that possibility is that my body temperature was elevated by 0.3℃ during the night—perhaps because of increased metabolic activity digesting all that food.

Interestingly, I got more deep sleep than I had all week up to now, perhaps because I went for a long run the day before. (Deep sleep is where you get the physical recovery from things like heavy weight-lifting sessions and long runs. Maybe the first few nights had less deep sleep simply because I didn’t need more than that, because I hadn’t had the hard workouts that require deep sleep for recovery.)

Here’s the next night, where I spent less time awake and almost as much time in deep sleep:

My body temperature was still up, though, even without the big meal. We had turned the thermostat down one more degree, but that’s about as low as we want it, so last night I rearranged the covers, removing the down comforter, going with just the wool blanket. I don’t know if that was a key change, but I slept very well last night:

Not only were my quantities of total sleep and deep sleep good, some of the other metrics were good as well. My temperature deviation was -0.3℃, which suggests that maybe I’ve got the covers and thermostat thing balanced just about right. My resting heart rate was down to 47, which suggests that I’ve recovered completely from the long run I took three days ago.

My hope is that by paying attention to this sort of thing, I can gradually eliminate these sorts of problems affecting my sleep. Of course that will leave me with the stress-related problems, but I think I know how to handle those—fixing the ones that can be fixed, accepting the ones that can’t be fixed, and engaging in appropriate self-care to help myself handle the stress better. And, of course, get enough sleep.

Resting heart rate

I’ve been tracking my resting heart rate. As you become more fit, your heart becomes able to pump more blood with each beat, so most people will see their resting heart rate decline with training. Fitness books suggest that there are other insights to be gleaned as well—an unexpected jump in resting heart rate may be a sign of overtraining, for example.

It’s only true in general; it doesn’t mean anything to compare resting heart rates across individuals. But I’m one of those who does see a strong effect, so it’s been fun to watch my resting heart rate decline. It’s up in the low 70s when I’m out of shape, drops into the 60s pretty quickly after I start getting some regular aerobic exercise, then gradually declines into the low 50s.

Yesterday, though, my resting heart rate was 49. Since my resting heart rate tends to get stuck in the low 50s, that was fun to see. It’s also a pretty good indication that I’m recovered from Monday’s long run.

Just two weeks to the winter solstice, so just four weeks until the days are again as long as they are now. Then things start getting better. That provides a ray of hope as I stick with the treadmill running.