ZOE Science & Nutrition - HRV vs. VO2 max vs. ECG: Which wearable metric ACTUALLY matters? | Prof. Malcolm Findlay

Starting point is 00:00:00 Welcome to Zoe Science and Nutrition, where world-leading scientists explain how their research can improve your health. The use of wearable devices that promise to transform our health is booming. But do they work? These watches and rings provide measurements and feedback to help you understand your health and take steps to improve it. measurements include sleep quality, step count and others but the metric getting a lot of attention right now is heart rate variability or HRV and there's no wonder HRV is said to be a good indicator of your stress levels

Starting point is 00:00:44 of your heart health and your overall well-being but is it really all that useful to track HRV is there anything else that would be better off tracking instead and how accurate are these wearable devices anyway. Joining us with answers is Professor Malcolm Finley, a board-certified cardiologist and electrophysiologist and an honorary professor of cardiovascular medicine and devices. A leader in the field of measuring heart health, he's well-positioned to give us the truth.

Starting point is 00:01:20 You'll leave today's episode, understanding whether a wearable device could help you, how to get the most out of it if you have one, and what are the best best. things to track to improve your health. Malcolm, thank you so much for joining me today. Thank you so much. Thanks for hearing me. It's a pleasure. Now, we have a tradition here at Zoe where we always start with a quick fire round of questions from our listeners.

Starting point is 00:01:44 And you can answer with a yes or a no or if you have to have one sentence answer. Okay. Can HRV tell you something about the health of your heart? Yes. Can wearable health tech help you look after you? your heart? I think so. Could focusing on the wrong numbers put your heart at risk? I think if you focus on the wrong numbers, you can do the wrong things and get the wrong idea. So I guess yes. Can two people with the same heart rate have completely different

Starting point is 00:02:14 HRVs? Oh yeah, absolutely. If you want to live longer, is HIV the number to focus on? If you want to live longer, there are lots of things to focus on and HIV is just one of the many things that you might use to guide you, but actually I think there are more sensible things you could use to guide you on focusing on HRV. And what's the most common myth that you hear about heart health? Okay, so the most common myth is that one thing, for example, concentrating on doing exercise, can negate concentrating on some really important medical issues such as high cholesterol. And so just looking after yourself in a general way doesn't negate the need for some proper medical intervention.

Starting point is 00:02:59 Well, I'm excited to get into all of that, Malcolm. And actually, for today's show, I woke up this morning. I thought, I'm going to actually wear two different types of watch, both of which tell my heart rate. It's thought it'd be quite fun to do that as we go through this. And they also tell me my heart rate variability, this HRV thing that you mentioned, which I know is hugely popular at the moment. What is HRV?

Starting point is 00:03:23 Yeah, 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 for 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. So the measures quite a mathematically complex measure that was first bought out in the 1970s, I think, as a way of guiding medical treatment and

Starting point is 00:04:02 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. Am 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

Starting point is 00:04:47 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, the 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. And so the HRV being higher, as measured by a watch, really indicates that 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? Because does that mean it's zero? It's almost zero. Okay. And that's because they've had the nerves to their new heart

Starting point is 00:05:31 essentially severed. And over time, there have been cases where people have developed a heart variability back in their new transplanted heart, probably because they've regrown some nerve innovation to their heart. So in an extreme scenario where you remove those nerves inputs, you get almost zero heart rate variability. And so zero is zero, is sort of bad, you would expect variability. Does everyone have basically the same level of this heart rate variability? Is everyone the same? The answer is no. Like any human parameter, things vary a great deal. So a sort of average number would be around 50, but it can be anywhere from the low 30s to the, you know, high 70s on the typical wearables. And that absolute number

Starting point is 00:06:15 doesn't really give you a huge indication on that person's health. And I think that's something we can talk about is how HRV, the exact number, doesn't help us a great deal, but the changes can really monitor whether or not someone's leading a more healthy lifestyle. The other thing, just to mention, heartwave variability goes down as you get older, pretty high in the teens, and then it's a downward trajectory ever after that. I'm already fascinated that what's normal is for it not to be steady, because I think in my mind's eye, you just want your heart beating regularly. The measures you're getting a measured in milliseconds, like that 50 number is a time variable. So let's not think that the heart is jumping around all over the place. That can be a sign of there being a actual medical

Starting point is 00:07:02 problem with the heart rather than it being a measure of health. And I think that in patients with an irregular heartbeat, atrial fibrillation, which is one of the things I see many of my patients with, heart rate variability actually is not a valid measure because in that case, the control systems of the heart have been overrun by abnormal heart rhythms. It's really a measure that's useful only in people who have the normal heart rate, the sinus rate. I think what you're saying is for a normal healthy person who's measuring their heart rate variability, actually their heart rate is very steady and there's this like very subtle changes going up and down. Exactly right. And you then said, however, if I'm seeing a bigger change,

Starting point is 00:07:41 you mentioned this word atrial fibrillation, I should be worried. Could you talk about that for a minute? Yeah, sure. So just to sort of back up, atrial fibrillation is a specific type of heart rhythm abnormality. the most common. About fifth of all people will experience it some time in their life. And actually it can be pretty serious, particularly if it's there the whole time. Not only it's serious, but it can be treatable. And all the wearables will alert people if they have possible atrial fibrillation or if it's detected atrial fibrillation. And basically, that's been a huge driver for the uptake of the ECG in wearable devices. Now, in that arrhythmia, the top

Starting point is 00:08:17 chain with the heart, rather than being triggered by the sinus node, which is the heart's own pacemaker, there's a electrical chaos going on in the top chamber of the heart, which completely overwhelms any control mechanism for the heart rate from that sinus node. And so the ending heart rate is completely irregular, and it's completely driven by these chaotic activities in the top chamber of the heart. And I think until someone like me, who puts it right and gets back into the normal rhythm, heart rate variability doesn't really come to play in the way we're talking about it today. It's a disease and it really needs specialist input. If I come back to the HRV, you mention that there's these different signals that are driving

Starting point is 00:09:01 what's going on. Could you help me to understand a bit more like what's controlling it and what's happening and why? The one we're familiar with is the way the heart rate increases when we do exercise, right? So that would be the fight-and-flight response. I mentioned that earlier, the sympathetic activity driving an increase in heart rate. But tugging against that is this idea that you have the nervous system that helps the body relax. So when one sleeps, that really pulls down the heart rate. And it used to be thought that either you are on one, either the sympathetic or the parasympathetic system were active. And, you know, if you're doing exercise, it would be sympathetic, and if you're relaxing, parasympathetic. But actually, in truth, both are working

Starting point is 00:09:43 at the same time, all the time, to slightly lower the heart rate or slightly increase the heart rate. And the exact ways they're working on the cells in the heart very, very slightly. And so the cells will be kind of the timing of those pacemaker cells will wobble from beat to beat. It won't be a precise clockwork. And that's the wobble that we're measuring in HRV. A bit like putting my thought on the accelerate. And a breath. And a breath. But actually, in a car, you're fairly driving test. You're driving the accelerator and brake at the same time. The human body and actually many complex control systems

Starting point is 00:10:18 have both an accelerator and a brake operating at the same time. I work out regularly because I'm told it's really good for my health. And since I started to have these watches, I actually notice my heart rate now and sort of see how it changes. And one of the things that I've been most struck by is that my heart rate changes fast. It goes up fast, but it also sort of comes down fast. Which I was quite surprised by

Starting point is 00:10:40 I sort of always assumed it was quite a slow and steady change But it seems like it can change in like a matter of I mean if you're going to be chased by a saber-tooth tiger You don't want to be waiting five minutes for your heart rate to get up Before you can run away So these are deep biological mechanisms Which have a huge survival advantage So if you need to do exercise

Starting point is 00:11:03 Your heart rate needs to be able to go up straight away And so when you talk about nervous system like does that mean that there's like sort of signals from my brain going straight through through nerves or the whole body's connected right so the brain what we think with is connected to the spinal cord which also supplies the hormone organs which will give out hormones for daily function and where I think we're getting more more used to the idea that every organ is connected to to the brain and every organ has an influence on every other organ in the body I mean it's where one body And now the heart, you know, when maybe I was in medical school, the overall thinking was this was a pump and it would just dial up and dial down.

Starting point is 00:11:44 But actually, there's this huge number of nerves innovating the heart. These are not directly from your thinking centers, but the thinking centers, the brain, do then pass signals down to influence the nerves actually supplying those heart muscles. And actually, in my PhD, several years ago, we were doing some experiments measuring the exact electrical activity in people. 's hearts whilst we were doing just thinking problems, active relaxation, or even something called anger recall, so we got people to imagine they were in a very stressful situation and then I'd act the sort of fool to get them very angry. But at the end of that, we were discovering that just having these thinking tasks, psychometric tasks, can directly affect the way the heart cells activate and relax, and the timings of which, the thing I was particularly interesting

Starting point is 00:12:35 there was how that could predispose to abnormal heart rhythms. I guess the key learning factor is that the influence of the brain to the heart is extremely deep. So we have these influences which are not just, you know, the heart being a pump, but the whole body connects. So when you are even just thinking about doing exercise, the heart will start to adapt to get ready to do that exercise. To sort of warming up. Exactly right. So if I understand it, Right. You're saying there's this sympathetic nervous system, which is the fight or flight, that's going to push my sort of heart rate up. And I've got this opposing system, the parasympathetic nervous system, which is sort of trying to get me to relax and is pushing it down. And these are both on all the time. And you're saying they're very subtly changing, maybe even by what I'm thinking that maybe there might be a saber tooth tiger or I'm thinking maybe I'm a bit tired or whatever those things are. And that's sort of adjusting my heart rate all the time. are you saying that there's both direct nerves but also there's these hormones

Starting point is 00:13:39 that we're here about. Exactly right. So the adrenaline hormone can be measured in the blood but almost more important is the direct nerve innovation to the heart's own pacemaker cells. And so I've got sort of both those things going on. Exactly. So it's not just the nerves.

Starting point is 00:13:54 There are hormones as well. So those nerves actually supply the glands that then secrete the hormones. So these things work as a single system. Can I change my heart rate without the hormones? Like, is there also direct link or is it? Yeah, no, there's a direct link.

Starting point is 00:14:08 And this is why it can be so fast? Exactly right. So actually in some medical testing we'll do on people's heart rates, we can stimulate nerves, which will increase and decrease people's heart rate. So we actually directly stimulate the tiny nerves supplying parts of the heart, which then we see the differences in their heart rate. That's fascinating. So you can literally adjust people's nerves to try and get these things back into.

Starting point is 00:14:32 Yeah, that's something we do to sort of work out where the best areas are, to do treatments, but, you know, there are potentially future treatments that are to come from that as well. So could we talk a bit about in today's world what is influencing sort of my HRV? Because I'm probably not going to see a saber-tooth tiger. What are the different factors that are likely to be influencing the HRV that, you know, I might end up measured with one of these devices? Yeah, so HRV, as we're seeing on our wearables, give a snapshot of how these nervous drives, are affecting the heart.

Starting point is 00:15:07 This measure can vary quite a great amount between different people, but for ourselves, day-to-day, it should be fairly similar. In many instances, the trends in that will be an indicator of one's overall sort of health status. So, for example,

Starting point is 00:15:22 if you have people who become unwell, get an infection, you would expect to see the heart rate variability decrease as the body is spending more time fighting in the infection, the sympathetic system, so that's the vital flight response, will be slightly elevated, and that heart rate variability tends to decrease. Likewise, the same thing's been seen, and people have had a heart attack,

Starting point is 00:15:45 art failure, or have quite severe diabetes. On the flip side, if people are, let's say, changing their lifestyles, improving what they do on a daily basis, getting a good night's sleep, for example, then we end up finding the heart rate variability will follow those trends, and you'd expect to see an increase in heart rate variability. So that number would generally increase over time. Now, you've mentioned a little bit sort of psychological stress, and I know you've actually done some research into the connection

Starting point is 00:16:17 between sort of the heart and the brain. Can you tell a bit more about how, as opposed to like maybe an infection, how does stress play into this? Does it increase my HIV? Yeah, so stress, again, would drive that fight-or-flight response in the way we generally think about mental stress. And so we'd expect things to decrease the HRV. Now, to be honest, the hardcore research into these things is not super well done.

Starting point is 00:16:39 But there's a wealth of evidence from patients with, for example, severe psychiatric disorders, clinical depression, as well as patients with severe autism, showing when people are in their worst states, their HIV is decreased. I've got to say, these researchers tend to be from before the wearable era. So these are patients being measured with your heart monitors over 24 hours and so on. But I think the data is a good one that we know that patients who are under severe mental stress will decrease the heart rate variability. It's not really that useful clinically to change treatments. It's really a follow-on. It's like an output measure. So if you've got someone who's needing mental health support, you may find as things get better and things improve, their heart rate variability increases.

Starting point is 00:17:32 But it's not great at telling us, oh, this person's heart rate variability is really low. They need mental health support or they need this doing to them. What you do to improve things, let's say, tends to come before the heart rate variability becomes useful. Before we move on, I'm conscious that both these watches, in fact, measure a lot of other. things to do with the heart beyond HRV. And I think we touch on them briefly. So heart rate is one that I definitely see. One of them says it can do an ECG, which is another thing I'm a bit unclear about what it is, except I've seen it on all those dramas on TV. What are those other things to do with the heart that you can get out of these devices? Okay, let me just say that ECG is one

Starting point is 00:18:12 of my favorite things in the world, right? So this is the direct measurement of the electrical activity of the heart. It's kind of incredible that just this tiny watch can give the real direct indication of those little electrical impulses within the heart, and that can be translated onto the screen on the watch or whichever all the wearables are available. These quality of the ECG are really clinical quality. You know, I make diagnoses based on the ECGs that I see from these wearable devices, and they are accurate devices. You would make a actual diagnosis based on the ECG that could come out of my Apple Watch.

Starting point is 00:18:51 Absolutely right. That is a direct measure of the heart's electrical activity. Every so often we have to be careful. But the majority of the time, I can make a really good diagnosis from the ECG, from a wearable technology. And that has really changed the world when we're looking at diagnosing irregular heart rhythms, diagnosing people with super slow heart rhythms, for example, and determining whether people need direct treatments. For those of us like me who still don't really understand what an ECG is, could you explain for a minute what it is? Yeah. So the ECG stands for electrocardiogram and this is the direct electrical measure. It's a tracing of the electrical activity of the heart and typically in the very first ones performed it was between the left arm and the right arm in buckets of salt water connected to a mercury galvanometer which flickered as the electrical balance change between the two arms, indicating the electrical transmission of the impulses through the heart. And that has gone from being these enormous contraptions, which you can see in the Science Museum, London, if you're interested, to being something that you can get for less than 100 quid to wear on your wrist. And the neat thing is that tracing is not just an interpreted number. That's the actual recording of those electrical flickers of the heart. And so knowing these

Starting point is 00:20:16 and knowing the normal timings between people, it becomes quite straightforward in one sense to then work out exactly what's going on underlying the patient or in the person who's having their ECG measured. What's the value of that? How does that tell me something about my health that's important? Yeah, if we just rewind 10 years, 10 years ago,

Starting point is 00:20:38 if somebody came to me, said, I feel like my heart goes irregular from time to time, we could say, okay, let's do a tracing of the heart, in the office, we'll do an ECG on the machine and actually they're not having arrhythmia at that moment. So they're not having the symptoms. But to get the diagnosis, we really need what's the term is symptom arrhythmia correlation. So we have to do the tracing when people are feeling the symptoms. And if you're wearing it the whole time in your wrist, you can now do that. Anyone with a wearable can do that. And that means that if one develops a abnormal irregular heart rhythm,

Starting point is 00:21:13 which, for example, atrial fibrillation, as we mentioned earlier, that can give an increased risk of stroke if it's not treated correctly. So now the watch can detect atrial fibrillation. People go to their GP, oh, I had these funny feelings. My watch says I have atrial fibrillation. GP can give a very simple blood thinner, which really removes that risk of stroke, not completely, but almost completely. People have different risk factors, so not everyone with atrial fibrillation is at risk of stroke, but certainly people over the age of 65 who develop atrial fibrillation, while that's really high on the radar or people with other health problems, that becomes a major risk. And so these wearables are not just something which is useful for people on a day-to-day

Starting point is 00:21:56 basis to monitor their health and improve their day-to-day health status, but can also prevent serious disease and really catastrophic problems. Now, it also measures my heart rate, which is different from the heart rate variability, right? Absolutely right, yeah. So the heart rate is how fast the heart is going, and we expect that to increase with exercise and decrease with rest.

Starting point is 00:22:18 And that's something which does have important health status implications, right? So if your heart rate drops low at night, well, that's a good thing. That's implying that you're sleeping very well, that you're having good rest, for example. Likewise, if people are increasing their heart rate significantly during exercise,

Starting point is 00:22:38 that's a measure that they're pushing their body. They will be getting benefit from the exercise they're doing. So these things are important, but they're measuring something different from HRV. One has to be kind of careful that big changes, sudden changes, may imply an artifact rather than being a true measure of one's heart health. A great example of that is if people measure an HRV on a day-to-day basis and it's always running about, let's say, just 55. and then one day they're particularly stressed and they measure it down at 20.

Starting point is 00:23:11 Well, that's far more likely just to be that because you're stressed you haven't attached your watch properly than a single measure being a measure of a change in your health status. It's really the consistent longer term, subtle changes which are a more direct implication of one's health status. Within those constraints, would you view these devices as basically quite accurate for these other measures? or are they like a long way behind sort of what you might use when somebody came in to you in the clinic? I think they fill this beautiful gap

Starting point is 00:23:43 between guesswork and clinical examination and measuring your pulse in the neck and so on when we're doing exercise. They fill this gap between that and essentially pretty hardcore medical investigations which are time-consuming, expensive. Wouldn't it be better if we had a way that people could just have that measurement straight away

Starting point is 00:24:04 and these wearables fill that gap. So I'm a huge fan of the wearables and a huge fan of people using that to take control of their own wellness and their own health. Now, you can spend a lot of money on these devices and there's a very big range of how much they cost between sort of the cheapest to the most expensive.

Starting point is 00:24:23 The key thing is one which measures the ECG, I think is important. The ones which just do a pulse rate, well, that has its own use, the older fit bits and so on. but they're not able to go to that next level of actually making that firm diagnosis. I actually don't think there's that big a difference between ones which are £1,000 and ones which are £40. In fact, just an experiment, I went on to a website that I didn't recognise and bought the cheapest one that I could find.

Starting point is 00:24:53 And, you know, other than the instructions being hard to understand and the user interface being pretty crummy, the actual results that gave me, the actual ECG trace that I was able to get from this, you know, $40 piece of plastic, we're actually pretty good. So they would be fine in the clinic. So you don't have to spend big bucks to get something which will do the job. Final question before we move on to like, okay, what's the actionable advice to people? Is there any science about the relationship between the food that we eat and these sorts of measures like HRV and the rest? Yeah, so there is one key factor, which is alcohol consumption's really been shown to be adverse on so many health metrics.

Starting point is 00:25:42 You know, low levels of alcohol consumption, people who claim vociferously that that's, you know, going to be bad for you. I'm not sure how solid that is. I think low levels, the social benefits are pretty huge, the social benefits for small amounts of alcohol consumption. But when one gets over, and I think the, UK government sort of recommendation of one, one and a half glasses of wine a day at the upper end, that's probably quite a good average for people to aim at where one can be confident that's not going to adversely affect one's health profile. So alcohol's number one. I think once we go beyond alcohol, one is really getting into the sort of secondary level effects of food. So if one has

Starting point is 00:26:27 a classically unhealthy diet that will have a whole heap of adverse health outcomes I guess which is likely then to be reflected in the heart rate variability but I don't think that it's fair to say that if you're just having a burger and chips that directly affects the way the heart rate controlled because you've had this over a long period of time I think this is yeah exactly right this is the long term habits the long term way people you know way people live their lives, which has those effects. And Malcolm, if I was to change my diet and really improve it, does that mean that over time I might actually see this HRV measure go up?

Starting point is 00:27:11 The answer is yes. Like, if you change your diet and particularly changing one's lifestyle, I think diet goes along a huge, it's not just the food on the plate. You know, it's associated with a whole bunch of other health activities. I think the food is going to be a huge part of that but I kind of suspect that's going to be reflected in the whole changing one's wellness and one's gut health and so on as well rather than it being just food directly affecting the heart rate variability.

Starting point is 00:27:40 Improve your diet, improve your lifestyle, you're less likely then to have to come and see me in a professional capacity. So I think having sort of helped us to understand what these measures are, I'd love to start to talk a bit about actionable advice. You've talked about the pros and cons of some of these different measurements, and I think, you know, my takeaway from HRV is that it might be a great measure of sort of an output of my health, but it's not necessarily something that sounds like I can change on a day-to-day basis. So 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 HIV is a useful measure. It's got some scientific basis, and it can,

Starting point is 00:28:24 can give an indication of one's health status, particularly the changes in an individual. So if I measure and compare myself to myself yesterday, my numbers last week, then I get an idea. There'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. Really, don't be worried. That's your own number and the changes in one's own number.

Starting point is 00:28:54 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. So 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.

Starting point is 00:29:24 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. It's pretty rare. In fact, I find it hard to think of times where people have spot 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 or something else changing. I think it's a little different if one's looking at it from a wellness point of view,

Starting point is 00:30:01 whereby you may want to say, okay, actually, I've made a change in my life, is this actually having an effect on my overall body's wellness? It's something to give themselves as a second encouragement, as a nice feedback to say, okay, I'm on the right path here.

Starting point is 00:30:20 But 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. I 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,

Starting point is 00:30:44 then you shift to the mid-30s to the mid-40s. Weeks are the timeframes where one can really be sure that any measurements 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 off at 8. And these things can make a big impact, and people have to, you know, accept impacts of

Starting point is 00:31:17 changing their life and adjust things accordingly to fulfill their health status. Do you have a friend who's obsessed by where a friend? devices. If you do, why not share this episode with them right now? I'm absolutely sure they'll thank you for it. All right. Well, I think we talked a lot about HRV. I'd love to talk about some of these other things. And I'd love to come back to your favorite thing in the world, ECG. Because you said that's amazing. I'm 50. As far as I know, you know, my heart is fine. How often should I run this ECG? What am I looking for? The ECG on the wearables, it's a great add-on, okay?

Starting point is 00:31:59 So most people, most of the time, won't need an ECG. Their hearts, you know, your heart's amazing. It just is so reliable. So an occasional ECG measured on your, if your watch has that functionality, take an ECG from time to time. That's going to be fine. It's kind of a fun thing to do. If people have symptoms of palpitations or they notice their heart skipping

Starting point is 00:32:20 or they've had a definite symptom of, hold on, I'm actually feeling way more tired or something's changed. Then it really gives a great hardcore indicator of what can be happening with their heart rhythm when they've experiencing those symptoms. And one of the neat things about the watches, of course, is you're wearing it the whole time. It will detect with the heart rhythm becomes abnormal just from the pulse function on the watch. And if that detect something which is abnormal, that can prompt you to then do the more advanced measure. the ECG just there and then

Starting point is 00:32:56 without having to come visit the doctor without having to go through your family doctor or... So one of the things I'm wearing is an Apple Watch and you're saying that might actually just notice that my heart rate is all over the place and it might actually trigger something? You can see a prom to regular rhythm detected and then you can get a proper ECG

Starting point is 00:33:13 perform from that same device. I think it's pretty amazing. I think that's extraordinary. Could we speak about heart rate now? Yeah. Because we had Peter Ateer on the podcast quite long time ago, and he spent much of the podcast talking about this idea of training at different levels of heart rate, these zones that you were talking about. How much value is there in looking at the heart rate? How much should I care that in my life I'm trying to get my heart

Starting point is 00:33:41 rate up to sort of certain levels during the day or during exercise? What's your... Yeah, so it can be useful, really, really useful to guide training and training fitness when people are trying to go for that 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? So 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. 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 what that means?

Starting point is 00:34:39 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. And in terms of heart health, are you saying that it's sort of getting to that level is the

Starting point is 00:35:14 thing that you are most telling your purchase 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

Starting point is 00:35:39 and they're finding it hard to stress themselves and they're saying, well, I'm not getting heart rates of 160, 170. Don't feel disappointed by that. If you're managing to boost your heart rate above 110, 120 beats minute, that's doing good. That's going the right way for people's health. How much time in the week should you be trying to get my heart rate above that 110, 120? Yeah. So different people have different lives and things are tricky, right?

Starting point is 00:36:08 I think it's clear that the more time, the better within reason. The standard of a bit of advice would be, see if you can get your do, about half an hour a day, I 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. What about sleep consistency? So I've noticed that actually on both these devices that are

Starting point is 00:36:51 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. 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

Starting point is 00:37:39 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 increases. You spend longer in these restful periods and have benefits from that. Is sleep consistency just getting eight hours sleep, or is it more than that? Yeah, although this may be, again, hugely varying between individuals, eight hours 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 chisling away at sleep at both ends

Starting point is 00:38:26 and one isn't having things which will stop one getting a deep night's sleep, getting enough REM sleep, for example. And 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 it has been useful in certain amounts of clinical 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. I think it can be super important in the clinical environment

Starting point is 00:39:15 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 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

Starting point is 00:39:37 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. 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?

Starting point is 00:40:05 I guess this is about you. 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. This is about you making yourself better for your own health and your own longevity and your own feeling of well-being.

Starting point is 00:40:32 Brilliant. Malcolm, I would love to do a little summary of what we've covered. So the thing that springs first of my mind is this thing where you said, ECG, my favorite medical thing in the world, these little devices on my wrist can actually measure the electrical impulses in my heart. And you're saying that if there is a problem, these are actually sufficiently accurate that you could use them for your own diagnoses and that you do do so. And so that's amazing. Now, if you don't have anything wrong with your heart, you shouldn't stress too much, but you can do it. But if you are having palpitations or anything like this,

Starting point is 00:41:06 actually, you can do this ECG and it could really capture that there's a real problem. And then you can go and see a cardiologist and they can actually really fix something which otherwise could end up in a life or death situation. You can imagine that brings that whole treatment forward by even months. People now can go to the doctor with a tracing which gives the diagnosis and then we can institute treatment straight away. We talked a lot about heart rate variability, HRV. And my understanding from this is like you think that is a useful measure of understanding

Starting point is 00:41:35 the state of my health. and it's something that's sort of like an output of the activities that I'm doing, like to improve my health, but also things that might be making me less healthy, like stress and having a virus, would actually be monitoring that more over weeks than on a sort of day-to-day basis and that the changes are going to be quite subtle. So I took away like I'm at 33, you know, if that changed to 38, that's actually quite a big shift. It's not going to suddenly change to 50. Yeah, if that's consistent, that is going to be something which is useful and worth measuring. And the reason why it's interesting is because actually all the time my heart has been pulled in these two different directions.

Starting point is 00:42:12 I've got this, I wrote this down, sympathetic nervous system, which is like fight or flight. So that's like pushing up my heart rate so I can run away from the saber tooth tiger. But on the other hand, I've got this relaxing system. You said the parasympathetic nervous system is sort of calming me down. And so the HRV is interesting because literally from one beat to another of my heart, these things are changing. and you want to have sort of somehow this responsiveness is a sign of, like, being healthy. Exactly right. So that little wobble in the heart rate, we're coming back to where we started, you know,

Starting point is 00:42:44 when we started talking, the subtle wobbles in the heart rate, which HIV measures gives this insight to the whole, whole body and whole heart health. And nutrition definitely matters long term. Short term, you said alcohol can have a sort of direct impact on this heart rate variability. But you were not saying you can. never have a glass of wine. You were saying something like, you know, don't have more than a glass of wine a day. That was sort of my takeaway. We talked about heart rate, which I thought was really interesting, where you were saying, you know, if you're literally doing exercise

Starting point is 00:43:15 training and trying to optimize that, then some of these, like, different levels of heart rate can be valuable. But actually, for most people thinking about maximizing their longevity and healthy years, the key is to get your heart rate sort of out of this resting zone. And you said that's probably like 110, 120. You want to get to that sort of number. And even if you're doing that for two hours across a week, that's going to be hugely beneficial. Yeah, absolutely right.

Starting point is 00:43:43 And then maybe finally I took away, you know, there are other measures that you think are interesting. Sleep consistency is really important. And it's a sort of thing that's going to drive your HRV. You're saying, like, if I can get that sleep consistency, it's supporting my health, I'm going to see it. And then although steps is like this old metric, Actually, you know, if you can hit 10,000 steps a day, this is going to do something really good for your health.

Starting point is 00:44:06 Keep active, right? That's what the step counts are showing you. And Malcolm, I think you now need to rush off to carry out some heart surgery. Is that right? Yeah, I think that's probably time, right? So that is definitely a Zoe first. We've had a few people who had to deliver babies, but heart surgery, this is brand new. Thank you so much for taking the time. I think we have better wrap up. That sounds pretty important. I really enjoyed it. Thank you so much. Thank you so much for having me. That's been great. I'll end this episode with something I think you'll like, a free Zoe gut health guide. If you're a regular listener, you know just how important it is to take care of your gut.

Starting point is 00:44:40 Your gut microbiome is the gateway to better health, better sleep, energy and mood. The list just goes on. But many of us aren't sure how to best support our gut. I wasn't sure before doing Zoe, which is why we've developed an easy-to-follow gut health guide. It's completely free and offers five simple, steps to improve your gut health. You'll get tips from Professor Tim Specter, Zoe's scientific co-founder and one of the world's most cited scientists, plus recipes and shopping lists straight to your inbox. We'll also send you ongoing gut health and nutrition insights, including how Zoe can

Starting point is 00:45:15 help. To get your free Zoe gut health guide, head on over to zoie.com slash gut guide. Thanks for tuning in and see you next time. You know what I'm going to be.

ZOE Science & Nutrition - HRV vs. VO2 max vs. ECG: Which wearable metric ACTUALLY matters? | Prof. Malcolm Findlay

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