ECG vs HRV vs VO2 max: Which smartwatch metric actually matters? with Dr. Malcolm Findlay

Is your smartwatch just a fun gadget, or a serious medical device? 

In this episode, Jonathan Wolf is joined by Dr. Malcolm Finlay, a leading consultant cardiologist, to explore the powerful health data available on your wrist.

They decode the most misunderstood metric, Heart Rate Variability (HRV), and reveal how your wearable can provide clinical-grade insights into your heart's health.

Dr. Finlay explains the counter-intuitive science behind HRV — why more ‘wobble’ in your heartbeat is a sign of good health — and breaks down the two opposing nervous systems that control it.

He shares the latest on how these devices can accurately detect serious conditions like atrial fibrillation and why he, as a cardiologist, trusts the ECG function on a consumer smartwatch to make diagnoses.

He also debunks common myths about heart rate zones, revealing the level of exercise intensity that truly benefits your long-term health.

The episode concludes with an empowering look at how this technology is shifting control into our own hands. Can a simple alert from your watch really help prevent a catastrophic event like a stroke? Discover which metrics matter most and how to use them to guide your wellness journey.

Make smarter food choices. Become a member at zoe.com

Try our new plant-based wholefood supplement - Daily 30+ *Naturally high in copper which contributes to normal energy-yielding metabolism and the normal function of the immune system.

Our new app gives you the power to see beyond the marketing

Make smarter, science-backed food choices in seconds. Scan. Score. Reveal the truth.

Download

Transcript

Jonathan: Malcolm, thank you so much for joining me today. 

Malcolm: Thank you so much. Thanks for having me. 

Jonathan: 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. You can answer with a yes or a no, or if you have to, a one-sentence answer. 

Malcolm: Okay.

Jonathan: Can HRV tell you something about the health of your heart? 

Malcolm: Yes. 

Jonathan: Can wearable health tech help you look after your heart? 

Malcolm: I think so. 

Jonathan: Could focusing on the wrong numbers put your heart at risk? 

Malcolm: I think if you focus on the wrong numbers, you can do the wrong things and get the wrong idea. So I guess, yes. 

Jonathan: Can two people with the same heart rate have completely different HRVs?

Malcolm: Oh yeah, absolutely. 

Jonathan: If you want to live longer, is HRV the number to focus on? 

Malcolm: If you want to live longer, there are lots of things to focus on, and HRV 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 rather than focusing on HRV.

Jonathan: And what's the most common myth that you hear about heart health? 

Malcolm: Okay, so the most common myth is that one thing, for example, concentrating on doing exercise can negate concentrating on some really important medical issue, such as high cholesterol. 

And so just looking after yourself in a general way doesn't negate the need for some proper medical intervention.

Jonathan: Well, I'm excited to get into all of that, Malcolm. Actually, for today's show, [when] I woke up this morning, I thought I'm going to actually wear two different types of watches, both of which tell my heart rate. I thought it'd be quite fun to do that as we go through this. 

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? 

Malcolm: Yeah. Heart rate variability is something you can measure from the heart rate. 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 with 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 measure is quite a mathematically complex measure that was first brought out in the 1970s, I think is 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. 

Jonathan: Am I healthiest if there is no variability in my heart rate and it's completely steady? 

Malcolm: It's the other way around. Absolutely the other way around. 

So the general idea of being healthy would be someone who has both control inputs into their heart, both the sort of fight and flight response. The sympathetic, that's the adrenaline drive, but also the relaxation drive, the parasympathetic, that works against that. 

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.

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? 

Jonathan: So does that mean it's zero?

Malcolm: It's almost zero. 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 innervation to their heart.

So in an extreme scenario where you remove those nerve inputs, you get almost zero heart rate variability. 

Jonathan: So if zero is sort of bad, you would expect variability. Does everyone have basically the same level of this heart rate variability? 

Malcolm: 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 thirties to the high seventies on the typical wearables. 

And that absolute number 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, heart rate variability goes down as you get older. Pretty high in the teens, and then it's a downward trajectory ever after that. 

Jonathan: 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.

Malcolm: The measures you're getting are 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 an actual medical problem with the heart rather than it being a measure of health. 

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.

We don't buy the hype — and neither should you

Our new app reveals what the food labels won't, using data from the world's largest nutrition study run by ZOE.

Download

Jonathan: 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 are these very subtle changes going up and down. 

Malcolm: Exactly right. 

Jonathan: And you then said, however, if I'm seeing a bigger change, you mentioned this word atrial fibrillation, I should be worried. 

Could you talk about that for a minute? 

Malcolm: Yeah, sure. So, just to sort of backup, atrial fibrillation is a specific type of heart rhythm abnormality. It's the most common; about a fifth of all people will experience it sometime in their life. And actually, it can be pretty serious, particularly if it's there the whole time.

Not only is it 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. Basically, that's been a huge driver for the uptake of the ECG in wearable devices. 

Now, in that arrhythmia, the top chamber of the heart, rather than being triggered by the sinus node, which is the heart's own pacemaker, there is 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. 

So the ending heart rate is completely irregular, and it's completely driven by these chaotic activities in the top chamber of the heart. 

I think until someone like me who puts it right and gets back into the normal rhythm, heart rate variability doesn't really come into play in the way we're talking about it today.

It's a disease, and it really needs specialist input. 

Jonathan: If I come back to the HRV, you mentioned that there are these different signals driving what's going on. 

Could you help me understand a bit more, like what's controlling it and what's happening and why? 

Malcolm: 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 is 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. 

It used to be thought that either you are on one, either the sympathetic or the parasympathetic system, were active. If you're doing exercise, it would be sympathetic. If you're relaxing, parasympathetic.

But actually in truth, both are working at the same time, all the time to slightly lower the heart rate or slightly increase the heart rate. 

The exact ways they're working on the cells in the heart vary 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. 

Jonathan: A bit like putting my foot on the accelerator…

Malcolm: And the brake, but actually in a car, you'd fail your driving test if you're driving the accelerator and the brake at the same time. 

The human body, and actually many complex control systems, have both an accelerator and a brake operating at the same time.

Jonathan: 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 see how it changes. 

One of the things that I've been most struck by is that my heart rate changes fast. It goes up fast, but also sort of comes down fast, which I was quite surprised by. I always assumed it was quite a slow and steady change, but it seems like it can change in like a matter of a few seconds. 

Malcolm: Yeah, 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, your heart rate needs to be able to go up straight away. 

Jonathan: And so when you talk about the nervous system, does that mean that there's signals from my brain going straight through nerves or…

Malcolm: 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. 

I think we're getting more and more used to the idea that every organ is connected to the brain, and every organ has an influence on every other organ in the body. I mean, we're one body. 

Now, the heart, when maybe I was in medical school, the overall thinking was this was a pump and it would just dial up and dial down. But actually, there's this huge number of nerves innervating 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.

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, relax. The timings of which, the thing I was particularly interested in 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.

Jonathan: Sort of warming up. 

Malcolm: Exactly right.

Jonathan: 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. 

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 that we always hear about? 

Malcolm: Exactly right. So the adrenaline hormone can be measured in the blood, but almost more important is the direct nerve innervation to the heart's own pacemaker cells. 

Jonathan: And so I've got sort of both those things going on.

Malcolm: Exactly, exactly. 

Jonathan: So it's not just the nerves; there are hormones as well. 

Malcolm: So those nerves actually supply the glands that then secrete the hormones. So these things work as a single system. 

Jonathan: Can I change my heart rate without the hormones? Is there also a direct link or is it…?

Malcolm: Yeah, a direct link.

Jonathan: And this is why it can be so fast. 

Malcolm: 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.

The crunch your gut’s* been craving.

Support gut health* and energy* and enhance the flavor and crunch of your meals.

Try Daily30+

Jonathan: That's fascinating. So you can literally adjust people's nerves to try and get these things back into… 

Malcolm: 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 have come from that as well. 

Jonathan: 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? 

Malcolm: Yeah, so HRV, as we're seeing on wearables, give a snapshot of how these nervous drives are affecting the heart.

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, 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 the infection. The sympathetic system, so that's the fight or 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, or have had heart failure, or who 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.

You'd expect to see an increase in heart rate variability. So that number would generally increase over time.

Jonathan: Now you've mentioned a little bit of psychological stress, and I know you've actually done some research into the connection between the heart and the brain. 

Can you tell me a bit more about how, as opposed to maybe an infection, how does stress play into this? Does it increase my HRV?

Malcolm: 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, 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 that when people are in their worst states, their HRV is decreased. 

I've got to say, these researchers tend to be from before the wearable era. So these are patients being measured with, you know, heart monitors over 24 hours and so on. But I think the data's 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. 

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. 

Jonathan: 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've touched 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?

Malcolm: Okay, let me just say the ECG is one 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.

The 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. 

Jonathan: You would make an actual diagnosis based on the ECG that could come out of my Apple watch.

Malcolm: 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. 

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. 

Jonathan: 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? 

Malcolm: 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.

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 changed between the two arms, indicating the electrical transmission of the impulses through the heart.

That has gone from being these enormous contraptions, which you can see in the Science Museum of London if you're interested, to being something that you can get for less than a hundred quid to wear on your wrist. 

The neat thing is that tracing is not just an interpreted number. That's the actual recording of those electrical flickers of the heart.

So knowing these and knowing the kind of normal timings between people, it becomes quite straightforward in one sense to then work out exactly what's going on underlying in the patient or in the person who's having their ECG measured. 

Jonathan: What's the value of that? How does that tell me something about my health that's important?

Malcolm: Yeah. If we just rewind 10 years. 10 years ago, if somebody came to me and 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, the term is symptom correlation. So we have to do the tracing when people are feeling the symptoms. 

Our new app gives you the power to see beyond the marketing

Make smarter, science-backed food choices in seconds. Scan. Score. Reveal the truth.

Download

If you're wearing it the whole time on your wrist, you can now do that. Anyone with a wearable can do that. And that means that if one develops an abnormal irregular heart rhythm, 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. 

So these wearables are not just something which is useful for people on a day-to-day basis to monitor their health and improve their day-to-day health status, but can also prevent serious disease and really catastrophic problems.

Jonathan: Now it also measures my heart rate, which is different from the heart rate variability, right? 

Malcolm: Absolutely. So the heart rate is how fast the heart is going, and we expect that to increase and decrease and with increase of exercise and decrease with rest. 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 are sleeping very well, that you're having good rest, for example. 

Likewise, if people are increasing their heart rate significantly during exercise, 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. 

Well, that's far more likely just to be that because you're stressed, you haven't detached your watch properly than a single measure being a measure of the change in your health status. 

It's really the consistent, longer-term, the subtle changes, which are a more direct implication of one's health status.

Jonathan: 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? 

Malcolm: I think they fill this beautiful gap between guesswork and clinical examination and measuring your own 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, 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.

Jonathan: Now you can spend a lot of money on these devices, and there's a very big range of how much they cost, between the cheapest to the most expensive. 

Malcolm: The key thing is one which measures the ECG, I think is important. You know the ones which just do a pulse rate, well, that has its own use, the older Fitbits 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 were a thousand pounds and ones which are 40 pounds. In fact, just an experiment, I went onto a website that I didn't recognize and bought the cheapest one that I could find. 

Other than the instructions being hard to understand and the user interface being pretty crummy, the actual results it gave me, the actual ECG trace that I was able to get from this $40 piece of plastic were 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. 

Jonathan: Final question before we move on to 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? 

Malcolm: Yeah, so there is one key factor, which is alcohol consumption's really being shown to be adverse in so many health metrics.

You know, low levels of alcohol consumption, people who claim vociferously that that's going to be bad for you. I'm not sure how solid that is. 

I think at 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 U.K. government 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 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 controls.

Jonathan: But if you've had this over a long period of time… 

Malcolm: I think this is the long-term habits, the long-term way people live their lives, which has those effects. 

Jonathan: 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. 

Malcolm: The answer is yes. If you change your diet and particularly changing one's lifestyle. I think diet goes a long… it's not just the food on the plate, you know, it's associates 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 in one's gut health and and so on as well as well, rather than it being just food directly affecting the heart rate variability.

Improve your diet, improve your lifestyle, you're less likely than to have to come and see me in a professional capacity. 

Jonathan: So I think having 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 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 I can change on a day-to-day basis. 

So maybe we could start with this question about the metrics that we should be tracking and maybe let's start with HRV. How should I be thinking about that? 

Malcolm: 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. 

So, 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.

Jonathan: 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. 

Malcolm: Don’t be worried. That's your own number and the changes in one's own number are going to be the key things to track on an individual basis.

Jonathan: How far does it need to change to care? Because that's the other thing I noticed is mine fluctuates around very little bit. So, if it goes from 37 to 33, is that a real difference? 

Malcolm: 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.

It'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, is 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, a hundred. So it might fluctuate between low thirties up to the low forties 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, say you're in the low thirties, low forties, then you shift to the mid thirties to the mid forties.

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 6:00 AM but you're still going to bed at midnight, you know, whereas before you were getting up at eight. 

And these things can make a big impact and people have to accept the impacts of change in their life and adjust things accordingly to fulfill their health status. 

Jonathan: Alright, 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, my heart is fine. How often should I run this ECG? What am I looking for? 

Malcolm: The ECG on the wearables, it's a great add-on. Okay. So most people, most of the time won't need an ECG. Your heart's amazing, it just is so reliable.

So an occasional ECG, 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.

But if people have symptoms of palpitations, or they notice their heart skipping 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're experiencing those symptoms. 

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 detects something, which is abnormal that can prompt you to then do the more advanced measure, the ECG, just there and then without having to come visit the doctor, without having to go through your family doctor.

Jonathan: 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.

Malcolm: You can see a prompt: irregular rhythm detected, and then you can get a proper ECG performed from that same device. I think it's pretty amazing. 

Jonathan: I think that's extraordinary. 

Can we speak about heart rate now? Because we had Peter Atia on the podcast quite a 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 rate up to a sort of certain levels during the day or during exercise? 

Malcolm: 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? 

So the key benefits probably come from doing not the extreme exercise, not extreme 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, everything about the body, longevity improves with exercise. 

Jonathan: When you talk about getting your heart rate up, how do I think about what 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 70. What does that mean when you're saying you want to get your heart rate up? 

Add a scoop
of energy*

Delicious. Crunchy. Energizing.

Get Daily30+

Malcolm: As standard, most people will find they're doing some brisk exercise, 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. 

Jonathan: And in terms of heart health, are you saying that getting to that level is the thing that you are most telling your patients they once do rather than trying to get it to 150 or 160 for some short period of time?

Malcolm: 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 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, don'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. 

Jonathan: How much time in the week should I be trying to get my heart rate above that 110, 120? 

Malcolm: 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 bit of advice would be, so 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. 

Jonathan: What about sleep consistency? 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. Maybe during the week I might go to bed at one time, and then maybe at the weekend I'm going to bed three hours later. Does this matter? 

Malcolm: Yeah, I think one of the key things about sleep consistency and the time that we're sleeping is, you know, the body's own day and night cycle rhythms don't really change on an individual day basis. 

So some things change, but your old whole hormonal clock, this idea of a circadian rhythm will be more or less fixed. And 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. 

The kind of interesting thing is that the 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 the benefits from that.

Jonathan: Is sleep consistency just getting eight hours of sleep? Or is it more than that? 

Malcolm: Yeah, 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 of 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. 

Jonathan: Finally, VO2 max. What is it? And does it matter?

Malcolm: 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. 

I 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 10 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 of 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, How's my general health doing metric, I'm not so sure how we can interpret that at the moment. 

Jonathan: Final question, should I be comparing myself against others with these metrics or is this only about like my own variation?

Malcolm: 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 are 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.

Jonathan: Brilliant. Malcolm, I would love to do a little summary of what we've covered. 

So the thing that springs first to 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 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, 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, you know, could end up like being a life or death situation.

Malcolm: And 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 instigate treatment straight away. 

Jonathan: We talked a lot about heart rate variability, HRV, and my understanding from this is that you think that is a useful measure of understanding the state of my health. 

It's something that's like an output of the activities that I'm doing to improve my health, but also things that might be making me less healthy, like stress and having a virus; we'd actually be monitoring that more over weeks than on a sort of day-to-day basis.

That the changes are going to be quite subtle. So I took away that I'm at 33, you know, if that changes to 38, that's actually quite a big shift. It's not going to suddenly change to 50. 

Join the community

Be the first to know about ZOE’s breakthrough research, content from the world’s leading scientists, and more.

Malcolm: Yeah. If that's co consistent, that is going to be something which is useful and worth measuring. 

Jonathan: And the reason why it's interesting is because actually, all the time, my heart has been pulled in these two different directions. I've got this, I wrote this down: sympathetic nervous system, which is like fight or flight, so it's like pushing up my heart rate so I can run away from the save tooth tiger. But on the other hand, I've got this relaxing system, you said the parasympathetic nervous system that's 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 this responsiveness as a sign of being healthy. 

Malcolm: Exactly right. So that little wobble in the heart rate we're coming back to where we started, you know, when we started talking.

That subtle wobbles in the heart rate, which HRV measures, gives this insight to the whole body and whole heart health.

Jonathan: And nutrition definitely matters long term. Short term, you said alcohol can have a sort of direct negative impact on this heart rate variability. 

But you were not saying you could 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, if you are literally doing exercise training and trying to optimize that, then some of these different levels of heart rate can be valuable.

But actually, for most people thinking about maximizing their longevity in 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.

And then maybe finally I took away, there are other measures that you think are interesting. Sleep consistency is really important, and it's the sort of thing that's going to drive your HRV, you're saying 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. 

Malcolm: Yeah. Keep active. That's what the step count's showing you.

Jonathan: And Malcolm, I think you now need to rush off to carry out some heart surgery. Is that right? 

Malcolm: Yeah, I think that's probably time. Right. 

Jonathan: So that is definitely a ZOE first. We've had a few people had to deliver babies, but heart surgery, this is brand new. Thank you so much for taking the time. I think we had better wrap up.

That sounds pretty important. I really enjoyed it. Thank you so much. 

Malcolm: Thank you so much for having me. That's been great.