Fitbit is a wearable device used to track physical activity and sleep. Ever wonder, how does Fitbit track sleep stages?
Sleep is regulated by two biological processes: circadian rhythms and homeostasis. Circadian rhythms regulate the timing of sleeping and waking up. Homeostasis regulates our need for sleep.
Generally, at least seven hours of sleep is considered a healthy sleep average, to ensure normal cognitive and behavioural functions. This includes memory recall, maintaining alertness and concentration for longer periods as well as reducing stress, anxiety and depression. Sleep helps in restoring mental and physical health by allowing the body to rest. According to studies, sleep helps remove toxins or waste by-products from the brain that accumulate throughout the day.
What are the sleep stages?
There are two sleep stages, commonly referred to as rapid eye movement (REM) and non-rapid eye movement (NREM). According to the American Academy of Sleep Medicine (AASM), a sleep cycle is divided into four stages with three of the stages involving NREM sleep and REM sleep making up the fourth stage. During sleep, a person usually undergoes on average between four and six sleep cycles each night. Each cycle begins with the NREM sleep and alternates between REM and NREM sleep stages.
In the first stage of NREM sleep, a person transitions from being awake to asleep. During this stage, the brain activity begins slowing down and the muscles start to relax.
The second stage, referred to as light sleep, begins after the person has fallen asleep and the eyes stop moving. During this stage, the muscles are relaxed, heart rate slows down and the temperature drops. It is usually easier to wake up during this stage.
The third stage, also known as deep sleep, involves the body repairing and rebuilding its tissues as well as strengthening the immune system. It is difficult to wake up during this stage. Those waking up from deep sleep generally experience disorientation or sluggishness.
REM sleep is the stage in which dreaming occurs. This stage begins around ninety minutes after falling asleep. In this stage, the eyes move rapidly and in random directions while the eyelids remain closed and the body does not move. During REM sleep, the brain activity is found to be similar to that of being awake.
How are sleep stages measured?
Polysomnography (PSG) is considered the standard method used to measure sleep stages. It is performed by a medical professional at a laboratory or clinical setting. This method comprises multiple tests including EEG and ECG that are conducted at the same time. The tests measure the brain activity, muscle activity, eye movements, heart rate and breathing.
Wearable devices can also be used to track sleep. They are generally designed as accessories (wristbands, smartwatches, clips or armbands) worn by the individual. These devices can generally be obtained without a prescription. Commonly used wearable devices such as Fitbit, initially designed as fitness trackers, can measure various bio-signals such as movement and heart rate. The data from these trackers can generally be used to help assess a person’s sleep patterns and quality.
How does Fitbit track sleep stages?
Fitbit devices are considered to be amongst the most commonly used wearable activity or fitness trackers around the world. These devices are generally worn around the wrist. There are several different models available designed as either wristbands or smartwatches.
The devices are embedded with an accelerometer sensor, which detects the body movements. The motion data helps determine the number of steps completed daily, distance covered, the amount of calories burned as well as the time spent on various physical activities such as exercise and sleep. Some models are built with a sensor used to record the heart rate.
Fitbit trackers can detect and track sleep. However, models such as the Fitbit Charge (designed as a wristband) and Fitbit Blaze (designed as a smartwatch) can also measure sleep stages as well as the heart rate during sleep and after waking up. The trackers can measure the sleep stages using a scoring algorithm that integrates body movement and heart rate variability (HRV), the change in time between each heartbeat. Heart rate variability fluctuates during transitions between the sleep stages.
The Fitbit tracker comes with an app, which can be downloaded to your mobile device such as a smartphone. The device generates a log that includes the sleep time and sleep stages data. Sleep time is the total number of hours you have slept each night. This information can be found in the Fitbit app and can help you identify and assess your sleep patterns.
In addition to your sleep log, you can also use the app to set your sleep goal. It is generally recommended to get at least around seven hours sleep to ensure proper physical and mental health.
Health activity trackers can be useful in providing information about your sleep patterns and quality. They can give you a general idea about your sleep health and help improve your sleep habits. However, these devices are not considered a substitute for medical diagnosis or treatment. Wearable devices are usually required to be validated against standard medical therapies such as polysomnography before they can be used for clinical purposes.
According to several studies, further research is needed to determine the accuracy of wearable sleep trackers such as Fitbit as well as their use in clinical settings. Talk to your doctor regarding any concerns about your sleep health. You can share the information recorded by the Fitbit device with your doctor.
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What should I know about Fitbit sleep stages? Retrieved from https://help.fitbit.com/articles/en_US/Help_article/2163.htm
How do I track my sleep with my Fitbit device? Retrieved from https://help.fitbit.com/articles/en_US/Help_article/1314.htm