What the latest fitness trackers are good for
Latest fitness trackers count more than your steps — there’s sleep, fertility, noise exposure and blood oxygen. But do we need it all?
As the reviews of Apple’s latest smart watch were published last week, much was made of its new star feature — something that less than a year ago few of us could have imagined caring about: a blood oxygen sensor.
In conjunction with an app, the Apple Watch Series 6’s oxygen monitor measures the oxygen saturation (SpO2) in users’ blood. Low blood oxygen can be an effect of COVID-19 and doctors have used SpO2 levels to determine the severity of patients’ conditions.
It’s the latest addition to an ever-expanding list of health data we can track, from sleep to fertility, handwashing and noise exposure. But do we really need it all? Evidence suggests that health trackers don’t necessarily make people healthier.
University of Oxford electrical engineering professor Lionel Tarassenko, a leading researcher of medical monitoring, says users tend to fall into one of two camps. “Some people become overly anxious, especially if a wrong reading occurs or the app or device is inaccurate, while others just get annoyed at the repeated reminders that these devices deliver.”
Yet some are useful, particularly during the pandemic. “Companies are accelerating the research into these devices, and ultimately if people use them properly it could make parts of (Britain’s National Health Service) more efficient,” he says.
Experts cite blood pressure monitoring as the next holy grail of wearables; at present most that promise to measure it require an extra device, such as a cuff. In 2015 Fitbit co-founder and chief executive James Park mentioned it as a metric that people would want to know, although it is complicated by the fact blood pressure cuffs typically need to cut off circulation to get a reading.
Which health trackers should we use and which can we lose? We look at the latest data offerings to see which are worthwhile.
Blood oxygen
How much oxygen you have in your blood provides important medical information and, while not a test for COVID-19, is useful in keeping tabs on the condition if it has been diagnosed but you don’t have severe symptoms or are recovering. In hospitals it is usually measured by a fingertip pulse oximeter.
“Most people have levels above 95 per cent blood oxygenation, but if they drop below 94 per cent and you have COVID-19 symptoms you should start to worry,” Tarassenko says.
“As COVID is a respiratory disease you can be seriously ill with it but display no symptoms and not realise that your blood oxygen is dropping to dangerous levels.”
You can buy a pulse oximeter online for about $70 or you can invest substantially more in the Apple Watch Series 6, from $599. The hi-tech version works via a function that reflects light through your wrist for a result after a 15-second reading. It also takes periodic measurements for your general blood oxygen status.
Verdict: Tarassenko describes home blood oxygen monitoring as “a game changer” in terms of health tracking during the pandemic. Apple says its measurements are not intended for medical use but as an insight into “overall wellness”, and unlike some of the cheaper pulse oximeters the device is not (yet) medically certified.
Tarassenko says it may not work as well if you have tattoos on your wrist and it can be temperamental; you need to have the device correctly positioned and sit perfectly still for it to record a measurement.
Still, he says that it’s a “credible and technically sound” device — he and scientists at Stanford University in California have discussed the design with Apple — and if technology floats your boat it’s worth trying.
“A finger pulse oximeter is still worth buying if not,” Tarassenko says. “Although if you are in general good health, you don’t need to keep check on blood oxygen levels.”
Worth tracking? Yes
Sleep
The tracking of sleep patterns is among the most popular data measurements, buoyed by a sweeping sense of paranoia that we are chronically sleep-starved.
There are two main stages: non-rapid eye movement sleep (non-REM) and REM sleep, the stage in which we dream and when our psychological and emotional networks are restored.
A complete sleep cycle, including both of the main stages, lasts 90 minutes on average, and too little sleep has been linked in some studies to health problems from weight gain and anxiety to heart attacks, asthma and depression.
“There’s no doubt that sleep is important for our health,” says Neil Stanley, a sleep scientist and the author of How to Sleep Well.
Verdict: You may think paying attention to our nocturnal habits can be only a positive thing, but Stanley says sleep trackers have limits.
“Sleep is a vastly complex signal to analyse and companies that make trackers have massively overpromised what they can measure,” he says. “Companies do claim to measure sleep stages, but they do so using their own unpublished algorithms that have not been scrutinised by the scientific community. Scientists use complex wiring and measuring of brain waves, called polysomnography, to read sleep stages, but fitness tracker manufacturers claim to get results by just measuring the movement of someone’s wrist.
“They might achieve 60 per cent to 80 per cent accuracy sometimes, but their figures are just an educated guess, and when their data is looked at by independent researchers it really is quite poor.”
Some, such as the Whoop, beloved of US sports stars and high-powered chief executives, also calculate the numbers of disturbances during your sleep to determine how efficiently you slept.
In 2017 Kelly Glazer Baron, an assistant professor at Rush University in Chicago, suggested that sleep tracking could prompt sleep problems rather than solve them because people became preoccupied with their sleep data, a condition dubbed orthosomnia.
“Some people do take it too far, and that can be stressful,” Baron says.
Worth tracking? No
Handwashing
We touch our faces about 23 times an hour on average. Ten of these touches are to the eyes, nose or mouth, the main pathways that can lead to bacterial or viral infection, which is why handwashing is one of the main defences against coronavirus.
Samsung and Apple have introduced features that remind you when to wash your hands, with alerts to do so the recommended six to 10 times a day and timers to push you towards the 20-second handwash recommended by the World Health Organisation.
The Apple version has a sensor that detects running water, while Samsung’s requires a swipe at the sink to set the timer.
Verdict: University of Reading associate professor in cellular microbiology Simon Clarke says the prompts are “a good idea”, but not foolproof.
“Handwashing can’t be standardised,” he says. “Someone who lives on their own and works from home doesn’t need to wash their hands as much as someone in a public-facing job, so there’s huge variation.”
There is likely to be a tipping point.
“This kind of reminder could generate obsessive behaviour or just prove annoying for some people,” Tarassenko says.
“We know we need to wash our hands, but being reminded of that every four hours could drive us crazy.”
Worth tracking? Possibly
Arrhythmia
According to the British Heart Foundation, about a million people in Britain are living with atrial fibrillation, the most common heart rhythm abnormality and a strong risk factor for stroke.
Irregular heart rhythms encourage blood clots to form, raising the risk of blood and oxygen flow being blocked to the brain.
It can be difficult to detect, and episodes can be sporadic and asymptomatic; as many as 25 per cent of people who have an AF-related stroke find out they have AF only after the event. At hospitals, electrical activity in the heart is measured by an electrocardiogram, but personal trackers claim to help you to keep tabs by measuring for irregularities.
Fitbit, with Massachusetts General Hospital and Harvard Medical School, and Apple, with Stanford University’s medical school, are working with cardiologists on studies that use their technology to identify heart rhythm irregularities. Because wrist-worn devices have a long battery life they can be worn for several days at a time, providing long-term heart rhythm assessment even when users are asleep.
Verdict: BHF senior cardiac nurse Julie Ward says: “For most people the absolute best way is to take your heart rate manually with finger on pulse.”
She adds: “Not all digital devices are sensitive enough to pick up arrhythmias and abnormal heart rhythms, particularly intermittent disturbances” and inaccurate readings can cause a spike in anxiety.
For people diagnosed with AF or other arrhythmia, some trackers may be useful.
“They are used to check when medication may be required, or if the medication being given for a particular arrhythmia is working,” she says.
“Or to monitor how frequently the arrhythmia is happening and whether the rate is fast or slow.”
Even then the jury is out. A study this year of heart patients published in the Journal of Medical Internet Research found the use of trackers was “more problematic than beneficial” because patients became overly anxious about results they misinterpreted as red flags.
Worth tracking? Possibly
Fertility
The market for fertility-tracking apps is huge. Some are plain menstrual cycle trackers, others claim they can predict a user’s “fertile window” based on the “calendar method”, or the theory that ovulation happens on day 14 of a woman’s menstrual cycle.
With more comprehensive apps you can input details about your weight and body temperature, which rises during ovulation, and other factors that might influence fertility.
“It’s an emerging area and a lot of the apps need tweaking,” Institute for Women’s Health, University College London, reproductive science professor Joyce Harper says.
Verdict: For a study published last month, Harper looked at 200 fertility-tracking apps on Apple’s App Store.
After removing those that were inappropriate because they were out of date or didn’t claim to predict a “fertility window”, she was left with 90.
More than half of these applied the “calendar method” of predicting fertility, which Harper has found in earlier studies to be flawed because only 13 per cent of women have cycles that last the “standard” 28 days.
“We found that a lot of free apps use more biomarkers than apps you are asked to pay for, so don’t assume you are getting a more reliable result because you’ve spent money on it.” In a yet to be published study she found many women became anxious that something was wrong if their period didn’t fall on the date the app said it should.
“To identify a woman’s fertile period, it is important that an app tracks other measures, such as basal body temperature, as cycle dates alone are not informative,” she says. “In general these apps are a good idea.”
Worth tracking? Yes
Noise exposure
According to government regulator the Health and Safety Executive, 17,000 people in Britain suffer from deafness, ringing in the ears or other conditions caused by excessive noise at work, and many more of us are at risk of hearing problems because of noise in our daily environment.
“Exposure to loud noise is one of the biggest causes of hearing loss. You don’t always notice the effects of noise-induced hearing loss until years after you were first exposed,” clinical audiologist Jesal Vishnuram says.
“Personal audio devices are the worst offenders.”
Verdict: Trackers that measure decibel levels and exposure to everyday noise can be useful. “The Apple watch has an app developed with the University of Michigan that is particularly good because of where it is worn on the wrist,” Vishnuram says.
“Hearing apps on smartphones tend to be less accurate, plus people throw their phones in a bag, which doesn’t help with noise detection, but they are still better than nothing.”
Worth tracking? Yes
The Times