Fitbit Charge Hr: Tracking Your Sleep, Including Rem

Fitbit devices with heart-rate tracking (excluding the Fitbit Charge HR and Surge models) can track sleep stages, including REM sleep. Fitbit devices use an accelerometer to track muscle movement and infer when the wearer is sleeping. If the wearer doesn't move for about an hour, the device assumes they are asleep. The accelerometer also measures the length and direction of every movement, including eye movement, to determine whether the wearer is in light sleep or awake. Fitbit's heart rate tracker measures heart rate variability (HRV) to estimate the different sleep stages. While sleeping, the device tracks beat-to-beat changes in the wearer's heart rate, which fluctuate as they transition between light sleep, deep sleep, and REM sleep. In the morning, users can sync their Fitbit device with the Fitbit app to view their sleep data, including time spent in each sleep stage and a sleep score. It's important to note that Fitbit's sleep tracking is not a substitute for medical diagnosis and should not be used as an alternative to tracking systems used by doctors.

How does Fitbit know when you're sleeping?

Fitbit devices with heart-rate tracking (except Fitbit Charge HR and Fitbit Surge) can be used to track sleep. Wrist-based Fitbit devices and Google Pixel Watch series automatically detect your sleep when you wear your device to bed. It is recommended to wear the device in a snug wristband while sleeping and not as a clip or pendant accessory.

Fitbit devices can detect when you are sleeping by tracking your movement and heart-rate patterns. When you haven't moved for about an hour, your tracker or smartwatch assumes that you're asleep. Additional data, such as the length of time of movements that are indicative of sleep behaviour (such as rolling over), can also help confirm that you're asleep.

While you sleep, your Fitbit device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV). These numbers fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, Fitbit uses movement and heart rate patterns to estimate sleep cycles from the previous night.

Fitbit's sleep feature estimates sleep stages using a combination of movement and heart-rate patterns. The overall sleep score is a sum of individual scores for sleep duration, sleep quality, and restoration, for a total score of up to 100.

How does Fitbit track sleep duration?

Fitbit devices automatically detect your sleep when you wear your device to bed. They record that you're asleep when your body is completely at rest and you haven't moved for about an hour. Fitbit devices that track heart rate (except Charge HR and Surge) also track sleep stages. They can estimate your sleep stages by using your movement and heart rate patterns.

While you sleep, your Fitbit device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, it uses your movement and heart rate patterns to estimate your sleep cycles from the previous night.

Fitbit estimates your sleep stages with 69% accuracy in any given 30-second time window. There is no systematic bias to how much light sleep, deep sleep, or sleeplessness Fitbit estimates. This means that if you use the app for many nights, you'll get a good sense of how often you tend to be awake, lightly asleep, or deeply asleep on a typical night.

Fitbit's sleep researchers and the National Sleep Foundation describe the following sleep stages:

• Light sleep: This stage serves as your entry point into sleep each night as your body unwinds and slows down. This stage typically begins within minutes of falling asleep. During the early part of light sleep, you may drift between being awake and asleep, remaining somewhat alert and can be easily awoken. Your breathing and heart rate usually decrease slightly during this stage.
• Deep sleep: This stage typically occurs in the first few hours of sleep. When you wake up feeling refreshed in the morning, you likely experienced solid periods of deep sleep the night before. During deep sleep, you become harder to be awakened since your body becomes less responsive to outside stimuli. Your breathing slows down, your muscles relax, and your heart rate usually becomes more regular.
• REM sleep: The stage associated with vivid dreams, REM sleep periods are typically longer as the night goes on. During this final stage of sleep, your brain becomes more active. Dreams mainly occur during REM sleep, and your eyes move quickly in different directions. Your heart rate increases, and your breathing becomes more irregular. In principle, muscles below the neck remain inactive to prevent you from acting out your dreams.

How do you view your sleep data on Fitbit?

To view your sleep data on Fitbit, you must first ensure that your Fitbit device is set up to track your sleep. This should be the default setting, but you can double-check by opening the settings menu on your device and making sure that heart rate monitoring is enabled. It's also important that you wear your Fitbit correctly when sleeping – it should be fastened snugly around your wrist so that the sensors are in contact with your skin.

Once you've awoken, you can view your sleep data by syncing your Fitbit device with your phone. You can then open the Fitbit app and view the sleep tile on the Today tab to see your sleep information. If you can't find the sleep tile, go to Settings at the bottom of the Fitbit Today screen and make sure it's turned on. You can swipe left on the sleep tile to find your sleep history for the past week.

If you have a Fitbit Premium account, you can access more detailed information in the Health Metrics dashboard. This includes long-term trends in your nightly breathing rate, heart rate variability, skin temperature, and oxygen saturation, as well as a comparison to averages for other people in your age group and gender.

To view your sleep stages, tap the Sleep Duration tile and then press and hold the Sleep Timeline graph. Move your finger left or right to check your sleep stages, and tap the Benchmark or 30-Day Average tabs for additional data.

What are the different sleep stages on Fitbit?

Sleep researchers divide sleep into five stages: stages 1, 2, 3, and REM. However, to keep things simple, Fitbit groups similar sleep stages together. In the app, your sleep will fall into three stages: light, deep, and REM.

Light Sleep

Light sleep serves as your entry point into sleep each night as your body unwinds and slows down. This stage typically begins within minutes of falling asleep. During the early part of light sleep, you may drift between being awake and asleep, remaining somewhat alert and can be easily awoken. Your breathing and heart rate usually decrease slightly during this stage.

Light sleep promotes mental and physical recovery. It takes up more than half of the night and is important because it's when your body processes memories and emotions and your metabolism regulates itself.

Deep Sleep

Deep sleep typically occurs in the first few hours of sleep. When you wake up feeling refreshed in the morning, you likely experienced solid periods of deep sleep the night before.

During deep sleep, you become less responsive to outside stimuli.

How does Fitbit's sleep tracking compare to clinical methods?

Fitbit's sleep tracking technology is based on movement and heart rate patterns. When a user hasn't moved for about an hour, the device assumes they are asleep. It also tracks the beat-to-beat changes in the user's heart rate, known as heart rate variability (HRV), which fluctuates as the user transitions between light sleep, deep sleep, and REM sleep. In the morning, the user can sync their device to view their sleep cycles from the previous night.

Polysomnography (PSG) is considered the gold standard for diagnosing sleep disorders and conducting sleep research. PSG involves simultaneous electroencephalographic (EEG), electromyographic, electrooculographic, and electrocardiographic assessments. PSG is typically conducted in a sleep laboratory, which can be uncomfortable and expensive.

Fitbit's sleep tracking technology has been compared to PSG in several studies. These studies found that Fitbit devices tended to overestimate total sleep time and sleep efficiency and underestimate wake after sleep onset, with no significant difference in sleep onset latency. Fitbit devices were found to correctly identify sleep epochs with accuracy values between 0.81 and 0.91, sensitivity values between 0.87 and 0.99, and specificity values between 0.10 and 0.52. Recent-generation Fitbit models that use heart rate variability and body movement to assess sleep stages performed better than early-generation models that only use body movement.

While Fitbit's sleep tracking technology can provide valuable insights into sleep patterns and quality, it is important to note that it is not a substitute for PSG or other clinical methods of sleep assessment.

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