Correlation between the circadian sleep propensity rhythm and hormonal rhythms under ultra‐short sleep–wake cycle

Circadian sleep propensity rhythms exhibited two peaks and one trough during the assessment.

• The sleep propensity rhythm showed clear peaks in the afternoon and at night, with a trough indicating the nocturnal sleep gate.
• The timing of the nocturnal sleep gate and nocturnal peak was correlated with temperature and melatonin levels.
• The afternoon peak timing was significantly related to habitual wake times and melatonin levels.
• Circadian rhythms of sleep propensity may be influenced by both internal biological clocks and individual sleep habits.

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