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

SPEAKER_1 (0:01)

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 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.

What is HRV?

Malcolm Finlay (0:48)

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 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 measure is quite a mathematically complex measure that was first brought out in the 1970s I think as a way of guiding medical treatment and risk prediction. I think in hardcore medicine, it didn't fulfill its promise in that people were trying to look for heart rate variability as a good predictor for future disease or future problems. But actually, it's 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.

SPEAKER_1 (1:59)

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

Malcolm Finlay (2:04)

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 fight and flight response, the sympathetic, that's the adrenaline drive, but also the relaxation drive, the parasympathetic, the 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 you've got those inputs really strongly affecting the heart. Let's take an extreme example. People with a heart transplant, you measure the HRV, it's completely flat. Why is it completely flat?

SPEAKER_1 (2:49)

Because that means it's zero.

Malcolm Finlay (2:50)

It's almost zero. That's because they've had the nerves to their new heart essentially severed. 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 the heart. So in an extreme scenario where you remove those nerves inputs, you get almost zero heart rate variability.

SPEAKER_1 (3:15)

Having helped us to understand what these measures are, I'd love to start to talk a bit about actionable advice. Yes. 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 Finlay (3:31)

Yeah. 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.

SPEAKER_1 (3:54)

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.

Malcolm Finlay (4:02)

Really don't be worried.

SPEAKER_1 (4:03)

Okay.

Malcolm Finlay (4:03)

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.

SPEAKER_1 (4:11)

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