Our lives are becoming more quantifiable all the time. As digital sensors increase in accuracy, drop in price and become easier to install, from the quality of your driving to the number of flights of stairs you climb each day, there’s a sensor (and an app) to help. And in the midst of this data-logging revolution is the science of sleep tracking.
Long before you could buy a wristband to count the number of zzz’s you bank each night, researchers have been investigating exactly what happens while we’re snoozing: it’s an essential part of our biological routine and yet there’s still a lot that we don’t know about how sleep works and how it affects our bodies. We can’t live without it, that much has been established, as anyone who’s gone one (or two) nights without sleep can testify; but there’s still a lot to learn about how the different areas of memory, creative thought, mood and other brain functions tie into sleep, and what exactly goes on in the brain while we’re snoozing.
There’s even some debate about whether monophasic sleep – one solid chunk of sleep a night – is even the best approach for us to function at our best. One school of thought suggests polyphasic sleep (sleep in several segments spread throughout the day), which concentrates on re-training your body to only attain the deeper part of the sleep cycle (REM), could be more beneficial for your energy levels if only working hours, family duties and social commitments allowed it. It’s been theorised that some societies, when reliant on candlelight, made it the norm to sleep early in the evening, then wake up for a few hours of candlelit activity before going back to sleep. It’s all still something of an unknown, though; the only fact we know for sure is that sleep, however you do it, is a vital part of being a functioning human.
These days there’s a plethora of cheap gadgets and gizmos designed to help you track the depth, length, and quality of your sleep without having to visit a university laboratory. Most fitness trackers will do the job, using the accelerometer inside the device to measure how much tossing and turning you’re doing and working out the quality of your sleep accordingly. Joining these basic trackers now are devices that are becoming more and more advanced: intelligent lights that mimic the slow rise of the Sun, mattress covers to adjust the temperature of your bed through the night, room sensors that can take noise and air quality readings to identify potential reasons why you aren’t getting much shut-eye, and so on. Anyone serious about monitoring their sleep patterns has a whole host of different gadgets to choose from.
The question is: do they actually work? With professional sleep scientists often stumped by the data gleaned from the lab, what are the benefits – if any – of falling asleep with a fitness tracker clamped to your wrist or nestled under your pillow?
Sleep-tracking gadgets and apps
Pick up a tracker or a smartwatch from the likes of Jawbone, Fitbit, Misfit, Withings or Pebble and chances are it’s going to have some form of sleep-tracking technology integrated into it. The accelerometer is the sensor most often used for this (the same one that works out how many steps you’re taking each day), though some also have a gyroscope to measure orientation and rotation, i.e. your movement.
Unfortunately for those wanting to learn the nuts and bolts of how these different trackers work, the manufacturers keep most of their cards close to their chest. Revealing how their proprietary algorithms work would be a little like revealing which spices are on KFC’s fried chicken or letting the cameras in on a Manchester United training session – no one wants to give anyone else any clues. Still, there’s plenty of information out there to piece together.
“During sleep mode, when your body is completely at rest and unmoving, your Fitbit tracker records that you are asleep,” explains Fitbit’s sleep-tracking FAQ. “A restless state of sleep indicates that your body transitioned [sic] from a very restful position with little movement to movement, such as turning over in bed. This doesn’t necessarily mean that you were fully awake or cognisant of your movements, but it may indicate that you were not getting the most restful sleep possible at that time.”
More of a rough guide, then, rather than a definitive record of sleep: if you’re lying in bed watching Netflix, for example, your Fitbit tracker is going to think you’ve dropped off. Trackers from other manufacturers work in more or less the same way. Jawbone’s UP3 adds more sensors to the mix. “The UP3 tracker uses bioimpedance sensors to automatically track your sleep and measure heart rate, respiration rate, body temperature, galvanic skin response as well as an accelerometer to detect four distinct stages of sleep: wake, REM, light and deep,” said a Jawbone spokesperson in response to our enquiries.
As well as movement, heart-rate is used to judge whether or not the wearer is sleeping and the quality of sleep they’re getting (assuming of course that the heart-rate sensor is accurate). Two temperature sensors are also used to log the temperature of the surrounding room and the temperature of the wearer’s skin. “While there is no true substitute for polysomnography [a professional sleep study] to obtain a complete medical evaluation of sleep, a strong correlation exists between the body’s movement patterns and its stages of sleep,” explains Misfit’s support documentation. “Utilising the same three-dimensional accelerometry- based technology that [the Misfit tracker] Shine uses to monitor your physical activity during the day, Shine tracks and analyses your body’s movements at night.”
The Beddit mattress sensor is also largely focused on how much moving around you’re doing when asleep. Proprietary algorithms then identify the most restful periods and label them as deep sleep, which brings us to the apps that come with each tracker: the quality of the data analysis in these apps can be just as important as the raw information coming from the devices. Jawbone’s app, for example, will present you with suggested goals and improvements based on previous data, for both sleep and physical activity. These can help users get to bed earlier, achieve a consistent bedtime, or catch up on missed sleep.
“We’re seeing it work,” Jawbone’s spokesperson told us. “For example, for a set of ‘Today I Will’s’ that challenged people to go to bed by a certain time, we see
that users who opt into bedtime TIW’s got 23 minutes more sleep based on a 40,000 person user test. That means they’re 72 per cent more likely to go to bed early enough to hit their sleep goal.”
The expert opinion
For those whose job it is to study sleep, devices way beyond the level of a Jawbone or a Fitbit tracker are required. The sleep laboratories dotted around the country are packed with sensitive equipment and cameras to study not just physical movement but also breathing speed, heart rate, blood oxygen levels and the electrical pulses that signify brain activity. They can’t quite see your dreams yet, but they’re getting close. These labs are used to deepen our understanding of the way sleep works and also to treat people with sleep-related problems. Insomnia is one obvious issue that needs treatment, but sleep apnea (where breathing temporarily stops), narcolepsy (feeling overwhelmingly tired) and hypersomnia (an inability to stay wake) are other common problems that can be studied in these labs.
We asked Professor Maarten De Vos of the Sleep and Circadian Neurosciences Institute (SCNi) at the University of Oxford to shed some light on how these professional sleep labs work, and whether a humble fitness tracker or mattress sensor could ever get close to logging the same level of detail. “We normally try to measure as many different variables as possible that can be informative in understanding sleep and circadian rhythms,” he told us. “These two concepts are intrinsically linked. If we sleep regularly, our circadian rhythm is stabilised. If you go at very irregular times to bed, it will be harder to fall asleep, leading to poorer sleep quality.”
For longer-term studies, the team at the SCNi use actigraphy devices (not dissimilar to a fitness tracker worn on the wrist), electroencephalography technology to monitor different sleep stages via brain activity and a variety of other equipment to get as much information as possible about the quality of someone’s sleep.
“You can think that you slept well or not, but how true this is can only be measured with external devices,” explained De Vos. “Because we have only very subjective ideas about our sleep, it is important to start measuring sleep parameters on a more systematic and objective basis and see how different sleep parameters are influenced by external factors and how these parameters influence normal physiology.”
It’s a complicated setup, and all of the data pulled from this range of hardware
has to be processed and analysed by the scientists working at the Institute, again using in-house algorithms designed specifically for the purpose. We asked De Vos whether consumer fitness trackers were any use at all in tracking sleep. “It is unfortunate… that [these trackers] all have proprietary algorithms to derive feedback,” he said. “Most of the time, these algorithms seem to be quite speculative, providing sometimes good estimates and sometimes completely wrong estimates.
“On the good side, the fact they provide feedback makes us aware that sleep is important, might enable us to find individual patterns that link to good or bad sleep, and allow you to make targets,” he added. So while your Fitbit may not be much use for a professional sleep study, if it gets you to increase the number of hours you’re asleep each night, then it’s proved its worth.
If you’re serious about wanting to improve the quality of your sleep, De Vos advises creating a regular day pattern covering not just sleep but also consistent meal times and light exposure. He also recommends avoiding the use of smartphones and tablets just before bed, because of the adverse effect the blue light they emit has on sleep quality, though there is software like F.lux available for both PCs and mobile devices to change this light to a more naturally occurring hue.
Testing the tech
So how do these gadgets work in practice? We took a Jawbone UP3, Fitbit Charge HR and a Misfit Beddit to bed and tested them with both an overnight sleep and a mid-afternoon snooze to compare them against each other. The Jawbone tracker was spot on with sleeping and waking times, and its app gave more detail than the others in terms of sleep: the three levels shown were REM, light, and deep. The Fitbit tracker also correctly identified when we fell asleep and woke up, though there was less detail here – the app only marks “restless” and “asleep” periods, which didn’t really match up with Jawbone’s data.
Beddit gives you a sleep score and a more detailed graph showing how deep your sleep is at regular intervals. It’s the most comprehensive of the apps and did the best job at recognising when we were actually sleeping properly and when we were just hitting the snooze button every ten minutes. If you really want some detailed feedback on your sleep patterns, we’d recommend getting hold of a mattress monitor, as the other advantage is you don’t have to wear anything while you’re in bed. Trackers from the likes of Jawbone and Fitbit seem to be more basic in their read-outs, although they can provide you with info on when you drop off to sleep and when you wake up again.
And for many, that’s going to be enough: having a record of the number of hours you sleep at night, and when you nod off, is a good first step towards a better understanding of your sleep patterns and a healthier sleep lifestyle. If you then want to go further, products like Beddit or the Sense device, which monitors room conditions, are worthy upgrades. But the hardware technology is only one part of the equation; you also need to be prepared to spend time analysing the data you’ve collected and making positive changes. Still, the good news is that if you are serious about sorting out your sleeping, there are plenty of products that can genuinely help.