Most replayed moment: What your wearable is really telling you | Dr Malcolm Finlay
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What is heart rate variability (HRV) and how is it measured by wearables?
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. 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 Finley to break down the data behind the devices. He explains how to turn confusing metrics into meaningful action, helping you adjust your training, manage stress, and make smarter decisions for your health. What is H L D?
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 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 measures, quite a mathematically complex measure that was first brought out in the 1970s, I think, as a way of guiding medical treatment and risk prediction.
I think in hardcore medicine, it didn't fulfil its promise in that people trying to look for heart rate variability as a good predictor for future disease or future problems. 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 it's the other way around.
Why does a higher HRV indicate better health and nervous‑system balance?
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. 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 that means it's zero. It's almost zero. Okay. And that's because they've Had the nerves to their new heart essentially severed. And over time, there have been cases where people have developed a heart rate variability back in their new transplanted heart, probably because they've regrown some nerve innervation to their heart. So in an extreme scenario where you remove those nervous inputs, you get almost zero heart rate variability.
Having sort of helped us to understand what these measures are, I'd love to start to talk a bit about actionable advice. Maybe we could start with this question about like the metrics that we should be tracking. And maybe let's start with HRV. How should I be thinking about that?
How should I interpret my personal HRV numbers and track meaningful changes?
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.
Malcolm, I was literally gonna ask that, because you mentioned fifty-five, and mine having seen this over the last couple of months is about thirty-three.
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Chapters
8 chapters
1
What is heart rate variability (HRV) and how is it measured by wearables?
0:01–2:04
2
Why does a higher HRV indicate better health and nervous‑system balance?
2:04–3:31
3
How should I interpret my personal HRV numbers and track meaningful changes?
3:31–5:14
4
Can HRV help me spot stress, illness, or lifestyle shifts before I feel symptoms?
5:14–7:01
5
What heart‑rate zones should I aim for during exercise for optimal health?
7:01–8:59
6
How does sleep consistency affect HRV and overall recovery?
8:59–10:37
7
What is VO₂ max, why does it matter, and can wearables measure it accurately?
10:37–12:36
8
Should I compare my wearable metrics to others or focus only on my own trends?
12:36–13:33
Speakers
1 identifiedMore from ZOE Science & Nutrition
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