Apple Watch Explains ‘Core Sleep’: What It Really Means

Fast Summary:

• Core sleep, as used in Apple Watches, refers to light sleep stages N1-N2.
• Apple opted for the term “core” rather of “light” to emphasize its importance; light sleep can constitute more than 50% of a typical night’s rest.
• Sleep stages recognized by scientists include:

– N1 (very light sleep): ~5% of total night’s rest.
– N2 (light or core sleep): ~45%, often associated with memory consolidation and basic physiological processes.
– N3 (deep sleep): ~25%, vital for body repair and immune system strengthening.
– REM: ~25%,associated with dreaming and brain activity resembling wakefulness.

• Wearables like apple Watches estimate sleep stages using movement data rather than advanced methods like EEG. This may lead to slight inaccuracies in stage differentiation.

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