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

From smartwatches to fitness trackers, more of us than ever are monitoring our health in real time. With just a glance at our wrist, we can check our step count, sleep quality, heart rate and, more recently, something called HRV. But what do these numbers actually mean? And more importantly, how can we use them to improve our lives? I’m joined by Dr Malcolm Finlay to break down the data behind the devices. He explains how to turn confusing metrics into meaningful action. helping you adjust your training, manage stress, and make smarter decisions for your health. 🌱 Try our science-backed and tasty wholefood supplement Daily30 🌿Let your gut microbes snack on the ZOE Gut Health Bar Get our brand-new app and Gut Health Test designed by world-leading gut health and nutrition scientists to build healthy eating habits 👉 Join ZOE Follow ZOE on Instagram. 📚Books by our ZOE Scientists The Food For Life Cookbook Every Body Should Know This by Dr Federica Amati The Appetite Reset by Dr Federica Amati Food For Life by Prof. Tim Spector Ferment by Prof. Tim Spector Good Mood Food (preorder) by Prof. Tim Spector Free resources from ZOE The Smart Snacking Guide: How to feed your gut, fuel your day, and snack without guilt The Hormone Harmony Guide: Tuning Your Body’s Internal Orchestra Eating for Better Brain Health: Your brain-gut blueprint How to eat in 2026 - Discover ZOE’s 8 nutrition principles for long-term health Live Healthier: Top 10 Tips From ZOE Science & Nutrition Gut Guide - For a Healthier Microbiome in Weeks Better Breakfast Guide Have feedback or a topic you'd like us to cover? Let us know here. Episode transcripts are available here.

• 0:01Speaker 00

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

• 0:10Speaker 00

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

• 0:46Speaker 00

  What is HRV?

• 0:48Speaker 01

  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 from 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, the whole day. So the measure's quite a mathematically complex measure that was first brought out in the 1970s, I think, as a way of guiding medical treatment and risk prediction. I think in

• 1:28Speaker 01

  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, that I think wearables have picked up on this measure, because you can take that and it gives another insight about your overall physical, general health and general health metrics.

• 1:59Speaker 00

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

• 2:04Speaker 01

  It's the other way around, absolutely the other way around. So the general idea of being healthy would be someone who have both control inputs into their heart, both the sort of fight and flight response, the sympathetic, that's the adrenaline sort of drive, but also the relaxation drive, the parasympathetic, that works against that. And having both inputs from the nervous system to the heart subtly changes how that beat to beat variability happens in the heart, and that is the HRV. 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?

• 2:49Speaker 00

  Because that means it's zero?

• 2:50Speaker 01

  It's almost zero.

• 2:52Speaker 00

  Okay.

• 2:52Speaker 01

  And that's because they've had the nerves to their new heart essentially severed. And over time, there have been cases where people have developed a heart rate variability back in their new transplanted heart, probably because they've regrown some nerve innovation to their heart. So in an extreme scenario, where you remove those nerves inputs, you get almost zero heart rate variability.

• 3:15Speaker 00

  Having sort of helped us to understand what these measures are, I'd love to start to talk a bit about actionable advice.

• 3:21Speaker 01

  Yes.

• 3:22Speaker 00

  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?

• 3:31Speaker 01

  Yeah. So first of all, I think HRV is a useful measure. It's got some scientific basis and it can give a, you know, 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.

• 3:54Speaker 00

  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.

• 4:02Speaker 01

  Really don't be worried.

• 4:03Speaker 00

  Okay.

• 4:03Speaker 01

  That's your own number and the changes in one's own number that are going to be the key things to track on an individual basis.

• 4:11Speaker 00

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

• 4:23Speaker 01

  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 changes preceded us being able to say there's something else that needs doing. Those measurements

• 5:03Speaker 01

  tend to be something that follow feeling unwell or something else, 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, body's, body's wellness? It's something to give themselves a second encouragement as a nice feedback to say, okay, I'm on the right path here. But, you know, it will get to a level and it will fluctuate around that level. I think it's never going to just keep on increasing up to 50, 60, 100. So it might fluctuate between low 30s up to the low 40s and keep fluctuating. If that's where you

• 5:48Speaker 01

  are, that's fine for you. I think those are quite, quite big variations. But it's a long-term shift from the, say you're in the low 30s, low 40s, 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 were getting up at eight. And these things can make a big impact and people have to, you know, accept impacts of change in their life and adjust things accordingly to fulfill their health status.

• 6:33Speaker 00

  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? What's your?

• 6:47Speaker 01

  Yeah. So it can be useful, really, really useful to guide training and training fitness when people are trying to go for their athletic targets, when people are getting their fitness targets. I think it falls down a little bit if we use the same idea, well, that's necessary to make the healthiest you possible. Right? 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. 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,

• 7:29Speaker 01

  the muscles, the strength, the bones, you know, everything about the body, longevity improves with exercise.

• 7:36Speaker 00

  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 something.

• 7:46Speaker 01

  60 or 70, yeah.

• 7:47Speaker 00

  What does that mean? When you're saying you want to get your heart rate up?

• 7:51Speaker 01

  Standard, most people will find they're doing some brisk exercise, some, you'll get into the realms of getting heart rates above 110, 120. That is definitely changing from a normal resting type activity to a formal exercise kind of zone.

• 8:12Speaker 00

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

• 8:22Speaker 01

  Yeah, I think that when you're getting to 150, 160, that is really starting to be exercise training. I'm not convinced that we've got great data that that improves the cardiac health more than a more subtle exercise. So if people are starting to go on an exercise program and they're finding it hard to stress themselves and they're saying, well, my, 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.

• 8:58Speaker 00

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

• 9:04Speaker 01

  Yeah. So different people have different lives and things are tricky. Right? I think it's clear that the more time, the better, within reason. The standard sort of bit of advice would be, see if you can 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, you know, 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.

• 9:48Speaker 00

  What about sleep consistency? So I've noticed that actually on both these devices that are on my wrist. And as I understand, it's sort of the measure of how much the time you go to bed or wake up varies. So it's not just how many hours you sleep for, but, you know, I'm guilty of this, like maybe during the week I might go to bed at one time and then maybe at the weekend I'm going to bed, you know, three hours later. Does this matter?

• 10:13Speaker 01

  Yeah, the body's own day and night cycle rhythms don't really change on a individual day basis. And that's why you get these jetlax. If you're travelling 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 jetlag. Now, the kind of interesting thing is that that quality of sleep does relate to the heart rate variability. So getting good quality sleep is like the input, and the heart rate variability is like the output. So if you improve your sleep consistency,

• 10:54Speaker 01

  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.

• 11:05Speaker 00

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

• 11:10Speaker 01

  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 sleep. But it's really making time so one isn't chiseling away at sleep at both ends, and one isn't having things which will stop one getting a deep night's sleep, getting enough REM sleep, for example.

• 11:36Speaker 00

  And finally, VO2 max. What is it and does it matter?

• 11:39Speaker 01

  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, 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

• 12:24Speaker 01

  thing that we can make actionable decisions on. As far as the accuracy and the usefulness on the wearables, I think jury's still out on that, other than as a measure of real exercise training. So if one's using that as a training metric, great. I mean, there's a science behind it. But if one's using that as a, like, how's my general health doing metric, I'm not so sure how we can interpret that at the moment.

• 12:51Speaker 00

  Final question. Should I be comparing myself against others with these metrics? Or is this only about like my own variation?

• 13:00Speaker 01

  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. 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 wellbeing.

• 13:34Speaker 00

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