Unravelling the Mystery of Fitness Trackers and Sleep

Over the past few years or so, the health and wellness industry has been having a massive surge in popularity. And from that very first release of the Fitbit tracker way back in 2009, to integrated fitness and sleep monitors built right into our watches today, the technology involved has certainly come a long way too. The more modern devices are now equipped with a wide range of sensors. And these sensors offer insights into several aspects of our day-to-day lives. From how physically active we are right down to how well we sleep. Or so they say.

As a species, us humans are constantly curious about the mysterious world of sleep. These trackers are a great way to gain a peep at some insight.And by helpingus to peel back that curtain, the sleep tracker aspect is a key selling point.

The question still looms however, as to whether these sleep-tracking features are actually accurate? And, do those accompanying sleep scores really mean anything? Let’s find out…

Accuracy of Sleep Tracking

These fitness trackers and other wearable devices use a combination of accelerometers, gyroscopes, and heart rate monitors to gather data, and infer sleep patterns. These sensos can definitely provide valuable information, however it’s worth noting that their accuracy is not perfect. The placement of the device, sleep variations unique to the wearer, and of course the quality of the sensors can have a huge effect on the reliability of the data provided by these devices.

Research has indicated that fitness trackers usually offer fairly reasonable accuracy when it comes to detecting sleep duration ( 1), but could struggle to distinguish between the different sleep stages we go through during the night. These sleep stages, like ‘light sleep’ and ‘REM sleep’, are critically important when trying to understand sleep quality. The devices can only estimate these stages, using movement and fluctuations in heart rate, which might not be as accurate as equipment used in sleep labs, for example.

Understanding Sleep Scores in Depth

We tend to like access to information quickly, and for it to be easy to understand and process; this is why fitness trackers are designed to distil vastly complex sets of data into a single, and easy to understand number. These “sleep scores” offer users a quick snapshot of their overall sleep quality, after considering multiple factors. Let’s look a bit deeper into some of the key aspects that typically add to the calculation of these scores:

1. Sleep duration

Definition: Sleep duration is the total amount of time spent sleeping, including all sleep stages.

Role in Sleep Scores: As a general rule, longer sleep durations contribute positively to sleep scores. However, excessively long sleep may also result in lower scores, as it may suggest inefficiencies in sleep cycles or underlying health issues.

2. Sleep consistency

Definition: This refers to the regularity and pattern of your sleep, like bedtime and wake-up time.

Role in Sleep Scores: Trying to maintain a consistent sleep schedule goes hand in hand with better sleep quality. Fitness trackers tend to reward users with higher scores due to them sticking to a regular sleep routine.

3. Sleep stages

Definition: There are different stages to sleep, like light, deep, and REM sleep. Each stage serves a specific purpose in the sleep cycle.

Role in Sleep Scores: Fitness trackers try to estimate the time spent in each sleep stage, by sensing movement and variations in our heart rate. Spacing out these sleep stages in certain ways, can contribute positively to the sleep score, reflecting a healthier sleep cycle.

4. Sleep interruptions

Definition: Fairly self-explanatory, it is just the amount of times we wake or are disrupted throughout the night.

Role in Sleep Scores: Uninterrupted sleep is usually seen as more beneficial, fitness trackers could well give higher scores to those who experience fewer interruptions, which emphasises the importance of uninterrupted rest.

5. Heart Rate Variability (HRV)

Definition: HRV measures the variation in time between each heartbeat, this helps to give us insights into the autonomic nervous system's activity.

Role in Sleep Scores: Some fitness trackers incorporate HRV into sleep scores; higher variability tends to be linked with better cardiovascular health, and potentially better sleep quality as a result.

It's important to note that the algorithms used by different fitness trackers vary, and the exact amount of weight placed on each aspect is likely to vary between different providers. It’s also worth noting that the interpretation of this data and sleep scores in general is fairly subjective. We should probably look at these scores as general guidelines, as opposed to absolute measures of our sleep health.

Interpreting Sleep Scores

1. Trends over time: It’s easier said than done, but try not to get fixated on individual scores, try t0 focus on trends over time instead. Are your scores improving or getting worse? Looking at general patterns can definitely be of more value than looking at specific data points.
2. Context matters: External factors that might impact your sleep on a specific night, like stress, illness, or changes in routine can have a huge effect on our ability to sleep well. A lower score on a particular night is probably understandable when looked at in context.
3. Individual variability: Try to recognise that sleep needs and patterns change from person to person. Comparing your sleep scores with someone else’s might not actually be of any use, as what works for one person may not work for another.
4. Seek professional advice: If you regularly experience sleep issues or if you’re worried about your sleep health in general, then the best thing to do is consult with a healthcare professional. Fitness trackers are valuable tools, but they should complement, not replace expert advice.

Sleep scores definitely provide us with an easy way to assess our sleep quality, however, we should try to use them with a balanced understanding. Consider and acknowledge just how multifaceted sleep really is. Looking at scores subjectively can lead to a more accurate understanding of our sleep health too. Prioritise the overall picture of your well-being, and try to use sleep scores as a supportive tool in your journey towards better sleep.

Tips for Improving Sleep with Fitness Trackers

Consistent wear

• Wrist placement: While wearing a fitness tracker, it’s important to make sure you wear it in a way where it won’t move around too much while sleeping. Try wearing it on your non-dominant wrist, as our dominant hand is likely to be more active throughout the night.
• Strap tightness: Making sure to wear the device snugly but not too tight is essential. A loose-fitting tracker is likely to move during sleep, which leads to less accurate readings, wearing the strap too tight however, could be uncomfortable, change the ease of blood flow, and impact the overall accuracy of heart rate monitoring.
• Consistent habits: Wearing a fitness tracker consistently is key, if you don’t wear it throughout the day, then make sure you get into the habit of putting it on before bedtime and removing it when you wake up. Consistency in wearing the device improves accuracy and the long-term assessment of your sleep patterns and trends. 

Regular calibration

• Device updates: Make sure to regularly check for updates from your provider. With most fitness trackers, there are semi-regular updates, which sometimes contain improvements to the algorithms used to gather data, this leads to an even more accurate representation of your sleep habits.
• Comparative assessments: Compare the data recorded by your fitness tracker with your own experiences of how you thought you slept. If you notice significant discrepancies, then try to recalibrate the device making sure to do so using the instructions provided by the manufacturer. This could involve adjusting specific settings or, in some cases, resetting the device to its factory settings.
• User feedback: Many fitness trackers ask for users to provide feedback, and while this often feels intrusive and irritating, it can be extremely important, as it offers the provider the chance to improve aspects of the tracker. This could lead to a better overall user experience, as well as potentially improving the accuracy of the data.

Combine data

• Subjective assessments: Take note of how you feel when you wake up, and what your personal subjective sleep experiences are, and compare them to the objective data provided by the fitness tracker, it should be fairly clear if discrepancies begin to appear.
• External factors: There are countless external factors that could effect the way you sleep, stress depression, diet, light, and of course sounds can make a huge difference. Fitness trackers aren’t likely to acknowledge any of these, so when assessing the data provided, don’t forget to factor that in.
•  Customisation: Some fitness trackers the user to input details about their day, such as caffeine intake, exercise, diet, or stress levels. Use these features to enrich the data captured by the device, with relevant contextual information.

Lifestyle adjustments

• Identify patterns: Keep an eye out for the trends and patterns in your sleep data to identify areas where there is room for improvement. For example, if you regularly experience poor sleep on nights where you have been to the gym, you may need to adjust your exercise routine or timing.
• Sleep hygiene: Make the most out of the insights gleaned from your fitness tracker, so you can evaluate and enhance your sleep hygiene practices. This could involve creating a relaxing bedtime routine, sticking to a consistent sleep schedule, or improving your sleep space by minimising light and noise, or getting a more suitable mattress for your needs.
• Goal setting: Use the data from your fitness tracker to set realistic sleep goals. That could be increasing the time you’re asleep, the consistency of your sleep, or trying to reduce disturbances; having realistic and achievable objectives can motivate you to make positive lifestyle changes. Super helpful!
• Consult professionals: Don’t forget, if things aren’t improving, you feel like you need additional support, or your health is being affected, then it is important that you seek professional advice from your GP. You need to prioritise your well-being.

By paying attention to these details and incorporating them into your daily routine, you can maximise the benefits of your fitness tracker and use the data to make informed decisions about your sleep habits and overall well-being.

Sleep Trackers: Our Conclusion

It’s safe to say that fitness trackers are a convenient companion, and can be a massively helpful way to gain insights into our sleep patterns, yet their accuracy definitely has its limitations. Sleep scores can provide a general and objective overview of sleep quality, but don’t take this information as gospel, the data should be interpreted with caution and a healthy dose of subjectivity. Remember, for people with serious sleep concerns, seeking professional advice is paramount.

As technology evolves and improves, more and more advanced sensors and algorithms are bound to enhance the accuracy of sleep tracking, but we should still stay vigilant, and look at these scores as supplementary information to give us an improved picture, rather than absolute measures of sleep health. They’re pretty nifty pieces of kit!