The first phase of REM sleep typically occurs after you’ve had an initial stage of deep sleep. This stage has also been shown to support your immune system. Adults may see a normal decrease in deep sleep as we get older, though sleep patterns vary among people.ĭeep sleep promotes physical recovery and aspects of memory and learning. Breathing becomes slower and muscles relax while heart rate usually becomes more regular.

During deep sleep, it becomes harder to be awakened since your body becomes less responsive to outside stimuli. When you wake up feeling refreshed in the morning, you’re likely to have experienced solid periods of deep sleep during the previous night. Deep Sleepĭeep sleep typically occurs in the first few hours of sleep. Light sleep promotes mental and physical recovery. Breathing and heart rate typically decrease slightly during this stage. You may be somewhat alert and can be easily awoken. During the early part of light sleep, you may drift between being awake and asleep. This stage typically begins within minutes of falling asleep.

Light sleep serves as the entry point into sleep each night as your body unwinds and slows down. The names of the stages are what we’ve chosen to use in your Fitbit sleep log.

When you sync your device in the morning, we use your movement and heart rate patterns to estimate your sleep cycles from the previous night.įitbit’s sleep researchers and the National Sleep Foundation describe the following sleep stages. While you’re sleeping, your 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. Additional data-such as the length of time your movements are indicative of sleep behavior (such as rolling over, etc.)-help confirm that you’re asleep. When you haven’t moved for about an hour, your tracker or watch assumes that you’re asleep. While this method is the gold standard for measuring sleep stages ( source), your device can estimate your sleep stages in a more comfortable, convenient way.įitbit estimates your sleep stages using a combination of your movement and heart-rate patterns. Sleep stages are traditionally measured in a lab using an electroencephalogram to detect brain activity along with other systems to monitor eye and muscle activity.

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