Most replayed moment: What your wearable is really telling you | Dr Malcolm Finlay

Tracking health data

0:00Hello, and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health.

0:10From smartwatches to fitness trackers, more of us than ever are monitoring our health in real time. With just a glance at our wrist, we can check our step count, sleep quality, heart rate, and more recently, something called HRV. But what do these numbers actually mean? And more importantly, how can we use them to improve our lives? I'm joined by Dr. Malcolm Finley to break down the data behind the devices. He explains how to turn confusing metrics into meaningful action, helping you adjust your training, manage stress, and make smarter decisions for your health.

Understanding heart rate variability

0:45What is HRV? Heart rate variability is something you can measure from the heart rate. Like the technical side of things is it measures the subtle changes in the beat-to-beat time differences of each heartbeat. When we talk about heart rate variability with watches and so on, it's not really the big changes that the heart rate will change when doing exercise or when you get excited about something or going to sleep at night. It's more like the subtle wobbles in the heart rate from beat to beat and looking at the course of that over several minutes or even over the whole day.

1:17So the measure's quite a mathematically complex measure that was first brought out in the 1970s, I think, as a way of guiding medical treatment and risk prediction. I think in hardcore medicine, it didn't fulfill its promise in that people were trying to look for heart rate variability as a good predictor for future disease or future problems. But actually, it's kind of a weak one compared to some other very serious medical testing that we have, for example, CT scans or MRI scans. But as a wearable device, I think wearables have picked up on this measure because you can take that and it gives another insight about your overall physical general health and general health metrics.

1:59Am I healthiest if there is no variability in my heart rate and it's completely steady? It's the other way around. Absolutely the other way around. So the general idea of being healthy would be someone who have both control inputs into their heart, both the sort of fight and flight response, the sympathetic, that's the adrenaline sort of drive, but also the relaxation drive, the parasympathetic that works against that. And having both inputs from the nervous system to the heart subtly changes how that beat to beat variability happens in the heart, and that is the HRV.

2:33And so the HRV being higher, as measured by a watch, really indicates you've got those inputs really strongly affecting the heart. Let's take an extreme example. People with a heart transplant, you measure their HRV, it's completely flat. Why is it completely flat? So does that mean it's zero? It's almost zero. Okay. And that's because they've had the nerves to their new heart essentially severed. And over time, there have been cases where people have developed a heart rate variability back in their new transplanted heart, probably because they've regrown some nerve innovation to their heart.

3:08So in an extreme scenario where you remove those nervous inputs, you get almost zero heart rate variability. Having sort of helped us to understand what these measures are, I'd love to start to talk a bit about actionable advice. Maybe we could start with this question about like the metrics that we should be tracking, and maybe let's start with HRV. How should I be thinking about that? Yeah. So first of all, I think HRV is a useful measure. It's got some scientific basis, and it can give an indication of one's health status, particularly the changes in an individual.

3:43So if I measure and compare myself to myself yesterday, my numbers last week, then I get an idea. It's no good me comparing mine to yours, because our baseline starting point may be different. Malcolm, I was literally going to ask that, because you mentioned 55, and mine, having seen this over the last couple of months, is about 33. So now I'm really worried that I'm really unhealthy compared to you. Really, don't be worried. That's your own number and the changes in one's own number that are going to be the key things to track on an individual basis. How far does it need to change to care? Because that's the other thing I notice is mine fluctuates around a very little bit.

4:18So like if it goes from 37 to 33, is that a real difference? As a one-off, that's probably not a real change. Let's say things are changing in a negative way. You'll probably be noticing other things having changed and be able to pinpoint, oh, actually, I've been in bed for the last two weeks with a flu, or I've had a minor operation, or it's been a particularly stressful part of my life. And that HRV will kind of be a reflection of those other things happening.

4:49It's pretty rare. In fact, I find it hard to think of times where people have spotted an HRV change, and only the HRV change has preceded us being able to say there's something else that needs doing. Those measurements tend to be something that follow feeling unwell or something else changing. I think it's a little different if one's looking at it from a wellness point of view, whereby you may want to say, okay, actually, I've made a change in my life.

5:19Is this actually having an effect on my overall body's wellness? It's something to give themselves a second encouragement, as a nice feedback to say, okay, I'm on the right path here. But, you know, it will get to a level, and it will fluctuate around that level. I think it's never going to just keep on increasing up to 50, 60, 100. So it might fluctuate between low 30s up to the low 40s, and keep fluctuating. If that's where you are, that's fine for you.

5:50I think those are quite big variations, but it's a long-term shift from the, say, you're in the low 30s to low 40s, then you shift to the mid-30s to the mid-40s. There are weeks of the timeframes where one can really be sure that any measurement is consistently changing. You know, most of the time when people have come to me specifically asking about HRV, it's been pretty easy to pinpoint, oh, hold on a sec, you've just changed your job. Now you're having to get up at 6am, but you're still going to bed at midnight, you know, whereas before you're getting up at 8.

6:24And these things can make a big impact, and people have to, you know, accept impacts of changing their life and adjust things accordingly to fulfill their health status.

Targeting exercise heart rates

6:33How much value is there in looking at the heart rates? How much should I care that in my life I'm trying to get my heart rate up to sort of certain levels during the day or during exercise? Yeah, so it can be useful, really, really useful to guide training and training fitness when people are trying to go for their athletic targets, when people are getting their fitness targets. I think it falls down a little bit if we use the same idea, well, that's necessary to make the healthiest you possible, right?

7:10So the key benefits probably come from doing not the extreme exercise, not extreme training. It's going to be getting outside of the resting zone, right? So when you start to significantly increase the heart rate, it's not just the heart that's benefiting, but the whole body, the whole blood vessels, the muscles, the strength, the bones, you know, everything about the body, longevity improves with exercise. When you talk about getting your heart rate up, how do I think about,

7:40what that means? So let's say I now have this device that says to me, you know, when I'm resting, my heart rate is 60 or something. 60 or 70, yeah. What does that mean when you're saying you want to get your heart rate up? A standard, most people will find they're doing some brisk exercise, some, you'll get into the realms of getting heart rates above 110, 120. That is definitely changing from a normal resting type activity to a formal exercise kind of zone.

8:12And in terms of heart health, are you saying that it's sort of getting to that level is the thing that you are most telling your patients it wants to do rather than trying to get it to 150 or 160 for some short period of time? Yeah, I think that when you're getting to 150, 160, that is really starting to be exercise training. I'm not convinced that we've got great data that that improves the cardiac health more than a more subtle exercise. So if people are starting to go on an exercise program and they're finding it hard to stress themselves and they're saying, well, I'm not getting heart rates of 160, 170.

8:47Don't feel disappointed by that. If you're managing to boost your heart rate above 110, 120 beats a minute, that's doing good. That's going the right way for people's health. How much time in the week should I be trying to get my heart rate above that 110, 120? Yeah, so different people have different lives and things are tricky, right? I think it's clear that the more time, the better within reason. The standard sort of bit of advice would be, see if you can do about half an hour a day.

9:20I think that's probably too much. I think there's good evidence that even if you're doing half an hour a week or two hours a week, for example, to half an hour every couple of days, that is going to be hugely beneficial compared to not doing anything. So more is better, but the most important thing is to be doing some. And once you're doing some, you'll notice the benefits remarkably quickly and being able to keep that as part of your schedule.

Sleep consistency and VO2 max

9:48What about sleep consistency? So I've noticed that actually on both these devices that are on my wrist. And as I understand, it's sort of the measure of how much the time you go to bed or wake up varies. So it's not just how many hours you sleep for, but, you know, I'm guilty of this, like maybe during the week I might go to bed at one time, and then maybe at the weekend I'm going to bed, you know, three hours later. Does this matter? Yeah, the body's own day and night cycle rhythms don't really change on a individual day basis.

10:20And that's why you get these jet lags. If you're traveling a huge amount, you will be going to sleep at hugely different times. And that's really disruptive for not just the time you sleep, but the quality of sleep. And you can end up having the direct feeling of jet lag. Now, the kind of interesting thing is that that quality of sleep does relate to the heart rate variability. So getting good quality sleep is like the input, and the heart rate variability is like the output. So if you improve your sleep consistency, you'd hope and probably even expect to see your heart rate variability increase as you spend longer in these restful periods and have benefits from that.

11:05Is sleep consistency just getting eight hours sleep, or is it more than that? You know, although this may be, again, hugely varying between individuals, eight hours is not going to be the right thing for everyone. Many people will feel great on six and a half hours sleep. But it's really making time so one isn't chiseling away at sleep at both ends, and one isn't having things which will stop one getting a deep night's sleep, getting enough REM sleep, for example.

11:35And finally, VO2 max. What is it, and does it matter? Okay, so VO2 max is a measure of the real exercise capacity of the body. It's a great metric, right? It's a great metric for athletes and for training, and has been useful in certain amounts of clinical health and clinical studies. It's been a useful research measure, hard to actually pin things on. And what one gets from the watches and what one gets from the wearable world, the importance of VO2 max outside of being a measure of exercise training is a bit indeterminate.

12:12I think it can be super important in the clinical environment, but even in the clinical world, I think it's been only in the last five to ten years, this is really coming into the fore as a useful thing that we can make actionable decisions on. And as far as the accuracy and the usefulness on the wearables, I think the jury's still out on that, other than as a measure of real exercise training. So if one's using that as a training metric, great. I mean, there's a science behind it. But if one's using that as a, like, how's my general health doing metric, I'm not so sure how we can interpret that at the moment.

12:51And final question, should I be comparing myself against others with these metrics, or is this only about, like, my own variation? I mean, one of the most important bits of advice I've ever been given was, don't care what other people think, right? I guess this is about you, right? This is about making oneself better, playing the cards you've already got, right? You're not going to be the same as your mate in the cafe or the pub. Things will be different. So these health metrics shouldn't be a competition between you and the person next door.

13:26This is about you making yourself better for your own health and your own longevity and your own feeling of well-being.

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