How Does Your Fitbit Track Your Sleep
A fitbit is a device worn to track movement such as walking, sleep or weight. There are several types of fitbits. Some fitbits are worn on the wrist like a watch. Another type of fitbit is worn over the ears like headphones.
The fitbit uses a 3-axis accelerometer to track patterns of movement. An accelerometer is an electromagnetic device that measures static forces and dynamic forces. An example of static force is gravity pulling your body toward earth. Dynamic force is due to movement or vibration. The accelerometer measures dynamic forces that cause the device to move or vibrate. A 3-axis accelerometer uses three separate accelerometers. Data from each accelerometer is sent to a central data collection site that uses software programed to interpret the patterns of movement.
According to Robotic Radio control Power electronic website, “There are many different ways to make an accelerometer! Some accelerometers use the piezoelectric effect - they contain microscopic crystal structures that get stressed by accelerative forces, which causes a voltage to be generated. Another way to do it is by sensing changes in capacitance. If you have two microstructures next to each other, they have a certain capacitance between them. If an accelerative force moves one of the structures, then the capacitance will change.”
A fitbit identifies the onset of sleep as lack of movement for about 1 hour. If the fitbit has a heart-rate tracker, the fitbit will use a combination of movement and heart rate to determine the stages of sleep. There are 4 clinical stages of sleep: N1, N2, N3 and REM (rapid eye movement)
N1 is a light drowsy stage of sleep that is not restorative. Healthy sleep consists of limited amounts of N1 sleep. A normal amount of N1 sleep is 10% or less of the total sleep time.
N2 is called stage 2 sleep. Many sleep researchers consider N2 to be the first true stage of sleep. In a sleep laboratory N2 sleep is identified by the slowing down of brain waves interspersed with occasional sharp quick waves or short burst of fast activity.
N3 is known as deep sleep or slow wave sleep. During N3 sleep breathing slows, body temperature decreases and blood pressure decreases. Deep sleep is characterized by large amounts of big brain waves occurring at a slow rate.
REM sleep: The body is very active during REM sleep and REM sleep is consider an active stage of sleep. Brain waves during REM sleep look very similar to brain waves occurring during wakefulness. During REM sleep the heart rate and breathing are irregular.
The stages of sleep are determined by movement and heartrate. The fitbit identifies the onset of sleep as the absence of movement for about one hour The fitbit measures heart rate by using an LED light. Blood passing by the LED light is measured and an algorithm determines if the movement and pulse are consistent with one of the 4 stages of sleep. Accuracy of fitbit recordings depends on wearing the fitbit on the recommended body part. For example if the device is made to be worn on the wrist, the device will record more accurately when worn on the wrist and not another body part such as an ankle.
The accuracy of how your Fitbit tracks your sleep is controversial. Sometimes the fitbit will report large amounts of a stage of sleep that is inconsistent with characteristics of sleep patterns at different ages. Tracking your sleep can be fun and useful if you don’t focus too much on the data. It might be more important to focus on are you getting adequate amounts of sleep rather than the stage of sleep. This is because how your Fitbit track your sleep stages could be inaccurate. For details about the stages of your sleep and sleep patterns, the polysomnogram remains the best way to measure this type of detail. The fitbit may work best for assisting you with identifying sleep onset, sleep duration and the end of the sleep period.
If you are considering purchasing a fitbit to record your sleep, you might be able to accomplish this is a free phone app. To find out if there’s a fitbit perfect for your needs, take the fitbit quiz: https://www.fitbit.com/compare