Health Update: Can your smartwatch really track your health accurately? – What Experts Say

Smartwatches are surging in popularity in Ireland.

A recent survey by Pure Telecom found that 61 per cent of adults in Ireland now use wearables to track their health and fitness data, becoming so essential to people’s fitness routines that 36 per cent will only work out if they are wearing their watch.

Dr Calibhe Doherty, Team Lead at the Cerberus project at University College Dublin, says one of the misconceptions is that people completely trust their smartwatches. Yet from his experience, people are also “very aware of the fact that there are limitations with smartwatches”.

So, how much should we count on these devices to monitor our health, and should we trust some metrics more than others?

How accurate are smart watches?

Dr Doherty told BreakingNews.ie the accuracy of wearables needs to be understood in a certain way.

“Wearable devices, for the most part, the latest generations, can give you a relatively accurate measure of your heart rate, of your cardiovascular fitness, and how much physical activity you’re doing.

“The error might be low, but the limits of agreement – the extent to which the error varies – is actually very great.

“So, on average, accuracy is good, but when you actually look at the individual data points, you see that there are times when it both over- and underestimates.”

Dr Doherty said that sometimes the accuracy is good, and sometimes it is bad – but when taken as an average accuracy for a single user of a specific period of time, this averages out to being “okay” accuracy, which “artificially inflates the apparent accuracy”.

“Often, researchers will take the second-by-second heart rate data and just say, well, how accurate is the device across the entire waveform across the 20 minutes of the test?

“That’s really problematic. You’re getting the average accuracy over the course of the test, which artificially inflates the apparent accuracy.”

So, what can I trust?

Dr Doherty said that users shouldn’t pay attention to specific values – for example, if your heart rate drops incredibly low or incredibly high for a limited period of time. Instead, he advises paying attention to trends over time.

“What you can do is over weeks and months and years, you can look at the trends of your heart rate in response to a given training session or exercise or a race or something like that. That’s where there is real value.”

“Never pay too much attention to the individual values because those individual values are inaccurate.

But you can look at the overall trends because ultimately what you’re seeing is the same level of inaccuracy plotted over time. So you don’t need to pay attention to the values; you just pay attention to the trends.

“A wearable device might tell you that you’re sleeping seven hours a night when you’re actually sleeping eight hours a night. It doesn’t matter whether it’s seven or eight.

“What matters is the fact that you’re sleeping X amount, and then something changes in your life, and you’re now sleeping more or less than that original X amount. You might have a newborn child or something like that, and suddenly you’ll notice that the line has gone down.”

Are some metrics better than others?

Most wrist-based smartwatches use photoplethysmography (PPG) sensors, which use light and a photodetector to measure changes in blood volume in skin tissue. This is used to measure heart rate, heart rate variability, and blood oxygen levels, among others.

Dr Doherty said that the more accurate metrics are those that are closer to the biosensing technology.

Some of the most inaccurate metrics would be energy expenditure (calories burned) and sleep quality. Heart rate, however, is generally more accurate.

“For energy expenditure, they could overestimate the amount of calories that you burned. They essentially double it during a session or underestimate by the same amount.”

“If we look at heart rate, or speed and distance, or step counts or other measures of physical activity, and then you look at energy expenditure and number of calories you burn, or sleep, the metrics that tend to be more accurately estimated tend to be the ones that are closer to the biosensing technology.

“So take heart rate. Heart rate is pretty much measured directly from the photoplethysmography sensor – the light on the back of your smartwatch. It’s measuring the changes in reflection of the green or the red light that is being shone through the skin on your wrist. And it is measuring waveforms. That’s all it’s doing.

“If you take something like energy expenditure, what’s going on there is you’ve got the core biometric signal, which is how many calories you’re burning. The sensing technology that’s being used to estimate energy expenditure includes heart rate, and accelerometry – how much your wrist is moving.

“It’s potentially measuring your body temperature and loads of other things. Here, the degree of separation between the sensing technology and the output energy expenditure is much, much wider.

“So there are all sources of errors, estimates and assumptions that the algorithm is making to estimate energy expenditure in this example that introduce bias and error.”

How healthy is it to track metrics?

Dr Doherty says that overall, the increase in use of smartwatches to track health and fitness is a positive thing.

“If we take sleeping as an example, wearable devices are not particularly accurate at measuring sleep. But what they do is they act as a mirror, they shine a light on your sleep behaviours.

“You might say, right, my sleep seems to be pretty poor, so I’m going to stop using my phone before bedtime.

“Whether the numbers that the device is spitting out are accurate or not isn’t the issue here. The issue is the behaviour change that is associated with simply paying more attention to this biometric outcome.”

However, Dr Doherty acknowledged that there are negatives too. Still using sleep as an example, he described  “orthosomnia” where “you get so caught up in the number or your sleep score, that you get into a negative feedback loop.

“You’re thinking about it all day. And then when you try to go to sleep earlier, you can’t sleep because you’re thinking about it.”

Dr Doherty also described a correlation between the heart rate variability metric and healthier behaviour.

Heart rate variability – the time between each heartbeat – is a measure of stress. Lower heart rate variability is considered less healthy than higher heart rate variability.

“One of the trends we’ve noticed is that people have noticed the extent to which alcohol will cause their heart rate variability to just bottom out.

“It can go really, really low, implying that alcohol is a stress on your system, it’s bad for you – which it is.

“We’ve noticed that people who wear wearable devices are far more conscious of that. There could be a situation where increased awareness of heart rate variability, the causes of decreasing heart rate variability, and understanding that alcohol causes a reduction in heart rate variability may lead to people not drinking as much.

“Now, is that a good thing? I think it is.”