Edit: specifically asking about wearables, like a Garmin watch that’s only tracking HR (and via that, HRV and breathing rate). Thanks!
In: 11
Sleep researchers have found four different stages of sleep that we go through. We call them N1, N2, N3 (sometimes split up into N3 and N4), and REM.
N1 is somewhere between awake and unconscious. N2 is the beginning of deep sleep. N3 is deep sleep. REM is a unique stage where there is increased brain activity while still unconscious.
Your brain is kind of like a computer. It works by neurons sending messages to each other as electric impulses (more complicated than that, but we’re just monitoring the electric signals with sleep trackers). The millions of electric impulses add up to form brainwaves. Even though these waves are very small, they can be picked up by electrodes on the skin of your head and amplified to read them by a computer.
Each stage of sleep has unique waveforms that we can use to identify what stage of sleep it is. As you fall in to stage N1, your brainwaves begin to slow down. As you enter stage N2 and become unconscious, your heart rate slows and your brain starts to make what are called “sleep spindles”, which are short bursts of faster brainwaves for a couple seconds before going back to slow brainwaves. At stage N3, your brainwaves become even slower.
Then you enter the REM stage, which is associated with increased brain activity, almost like you’re awake, even though you’re still unconscious. This is the dream state. It is easily detected by eye movement, where it gets its name: Rapid Eye Movement.
Each of these cycles from N1 to REM takes about 90 minutes or so. After REM, you go back to stage N2 sleep and start the cycle over. This repeats until you wake up.
Here’s some more info on the sleep cycle:
https://www.sleepfoundation.org/stages-of-sleep
Latest Answers