REM sleep

What it is

REM (rapid eye movement) sleep is distinct from non-REM sleep in three main ways: the rapid eye movements it’s named after, changes in breathing pattern, and brain activity that resembles being awake. It recurs several times a night as you cycle through sleep stages.

Why it matters for training decisions

REM is a normal, necessary part of a night’s sleep, but there’s no well-established REM target for athletic performance. If REM looks low, the most practical response is usually to protect total sleep time and regular timing, and to look at things that commonly disrupt sleep, such as late alcohol, rather than to chase the REM number itself.

How wearables measure it, and the limits

Wearables estimate REM from movement, heart rate and breathing patterns rather than brain activity. In an independent comparison of consumer trackers against lab polysomnography, sleep stage results were inconsistent across devices, and accuracy dropped on disrupted nights. Apple Watch reports REM as one of three sleep stages, alongside Core and Deep.

Use REM trends cautiously, and don’t read much into a single night’s change.

How P247 uses it

P247 reads REM sleep from Apple Health along with your other sleep stages. REM isn’t one of the inputs to P247’s recovery score.

This glossary is general information to help you understand your training data. It isn't medical advice, diagnosis or treatment. For injury, illness, medication, blood test results or any health concern, speak to a qualified health professional.

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