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Friends, let’s talk about one of the most confusing terms you’ll see on your fitness tracker—specifically your Apple Watch. Next to REM sleep, which you’ve probably heard of, and “deep” sleep, which feels self explanatory, there’s “core” sleep. And if you google what core sleep means, you’ll get a definition that is entirely opposite from how Apple uses the term. So let’s break it down.
The root of the confusion lies in the fact that the term “core sleep” has been used in the scientific literature to mean a few different things. Importantly, it’s not a recognized sleep stage. Apple, on the other hand, decided to rename the sleep stages its watch can detect, and called one of them “core sleep”—but it bears no relation to any of the previous common uses of the term.
It’s Time to Learn What ‘Core Sleep’ Actually Is
