Sleep science in plain language
Deep sleep, REM, sleep cycles and the circadian clock explained without jargon, with what each one means for recovery and performance.
Guides
- REM vs Deep Sleep: What Each Stage Does and Why Athletes Need BothDeep sleep (N3) is slow-wave sleep concentrated in the first hours of the night and linked to growth hormone release and physical recovery. REM sleep is a brain-active, dream-rich stage concentrated toward morning and linked to emotional processing. You need both, so cutting either the start or the end of the night costs you something.7 min read, 8 sources
- Sleep Cycles Explained: How Long They Last and What Happens in Each OneA sleep cycle is one pass through light sleep (N1, N2), deep sleep (N3) and REM sleep. In a lab study of more than 6,000 cycles, the median cycle lasted 96 minutes, the first cycle was shorter, and length varied widely between people. Most adults complete four to six cycles a night.6 min read, 7 sources
- Circadian Rhythm Explained: Your Body Clock, Light, Sleep and the Best Time to TrainYour circadian rhythm is a roughly 24-hour internal clock, run by the suprachiasmatic nucleus in the brain, that times sleep, alertness, hormones and body temperature. Light reaching your eyes is its main reset signal. Morning daylight moves the clock earlier, bright evening light pushes it later, and a regular wake time keeps it stable.6 min read, 10 sources