If you plan to invest in a fitness tracker, think about the model’s essential features. One of these is sleep tracking. Sleep tracking can be a handy feature, especially for people who have trouble sleeping and professional athletes.
With that said, sleep tracking on its own is quite complicated, so it begs the question of how do fitness trackers track sleep. This article discusses sleep tracking, how the app works, and more.
What is Sleep Tracking?
Before we talk about how sleep tracking works, let’s describe what it actually is. First, of course, sleep tracking tracks your sleep, but it’s a little more complicated than that because there are various components to sleep tracking.
First, a decent sleep tracker should track how long you sleep; it will record when you fall asleep and wake up.
Second, a sleep tracker will measure the quality of your sleep by detecting when you toss and turn, as well as when your sleep gets interrupted.
Third, a good fitness tracker can also measure your sleep phases. As we will discuss below, there are various sleep phases that humans go through. A good fitness tracker can estimate how long you are in each of these phases.
Higher-end fitness trackers have other features and record environmental factors in a room. These include temperature and ambient light.
Some models may ask you to enter information about various activities in your life that can affect sleep. This can include things like diet, caffeine consumption, and stress levels.
A Typical Human Sleep Cycle
It’s important to know what comprises an actual sleep cycle. There are five main stages of a normal sleep cycle.
The first stage is a very light sleep that is easy to wake from, and it lasts just a few minutes. During the second stage, your brain waves start to slow down, which is relatively light sleep.
Stages three and four are much deeper, and waking up is much harder during these cycles. During sleep cycles stages three and four, your body repairs itself, grows and boosts immune functions.
The final stage of the sleep cycle is known as REM, or rapid eye movement. This is when you start to dream, and your brain becomes much more active.
This sleep cycle generally repeats itself every 90 and 110 minutes. Furthermore, the REM stage increases in length as you go through more sleep cycles.
Tracking Sleep with Actigraphy
Now that you know what sleep cycles look like, let’s look at how sleep tracking works. Basic fitness trackers or sleep trackers will use what is known as actigraphy to determine when you are asleep or awake.
Actigraphy uses a 3-axis accelerometer which is designed to measure your movements. This is done mainly through the use of a gyroscope.
Various parameters have been programmed into the unit. These algorithms make sense of your body’s movements during your sleep. In theory, using an accelerometer to measure your body’s activity is very simple. For instance, if you are very still and not moving, it will assume that you are asleep.
In addition, some sleep trackers incorporate other metrics into their measurements, such as breathing rate and heart rate, into the equation.
Simply put, when you are deep asleep, your breathing and your heart rate slow down. So this is another way in which sleep trackers can determine whether or not you are sleeping.
Actigraphy vs. PSG
Actigraphy is fine for use with basic sleep trackers. However, it is not the method of choice in terms of accuracy. For overall accuracy, the gold standard is known as PSG or polysomnography.
This involves using an EEG test, where various electrodes are attached to your head to measure your brain waves. This is far more accurate than actigraphy. Although that said, it’s not a realistic feature to have on a wearable sleep tracker.
Sleep Tracking Accuracy with Actigraphy
Good fitness/sleep trackers will be pretty accurate. However, as mentioned, it’s not the most accurate when tracking your sleep cycles.
The simple fact is that actigraphy tracks movement, and this is generally not enough to determine your sleep cycles or stages. On the other hand, PSG is used for professional purposes because it measures brain waves.
This is generally the only way to determine which stage of a sleep cycle you are in. That said, most basic sleep trackers are accurate enough to know when you are awake or asleep. They should also tell when you wake during the middle of your sleep.
However, some lower-end sleep trackers may not be overly accurate in this sense. Some may think that you are asleep just because you aren’t moving, such as if you are lying down and watching TV. In addition, many sleep trackers need you to turn on the sleep tracking function before you go to sleep.
The Benefits of Sleep Tracking
Sleep tracking is beneficial for people who have trouble sleeping and professional athletes.
Your body needs sleep to heal, and sleep trackers can help improve the quality of your sleep. They provide the information necessary about your sleep patterns and quality.
Therefore, you can then make adjustments as necessary to sleep better. Many sleep trackers will also provide advice on how to sleep better.