Fitbit is a wearable device used to track physical activity and sleep. Ever wonder, how Fitbit tracks 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 behavioral 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, the 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, 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 in a laboratory or clinical setting.
This method comprises multiple tests including EEG and ECG that are conducted at the same time. The tests measure 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.