Sleep cycles through four stages: N1 (light onset, 1-5 min), N2 (light sleep, 10-25 min), N3 (deep/slow-wave sleep) and REM (rapid eye movement). Deep sleep (N3) is when physical recovery, muscle repair and growth hormone release peak. REM is when memory consolidation and emotional processing occur. Athletes deprived of deep sleep show reduced muscle recovery and performance. A typical 90-minute sleep cycle progresses N1 → N2 → N3 → N2 → REM; most adults complete 4-6 cycles per night.
Key points
- N1, N2, N3 (deep), REM stages
- N3 deep sleep = physical recovery, GH release
- REM = memory consolidation
- 4-6 cycles of ~90 min per night