= 生理時鐘 = 晝夜節律
Circadian rhythm is the conductor of your body’s orchestra/symphony.
The circadian rhythm is an internal biological clock that governs/modulates the sleep-wake cycle. It operates on a roughly 24-hour cycle, responding primarily to light and darkness in the environment.
- Generated from within, but synchronized (entrained) by external cues 1, especially light.
- Found in almost all living organisms, from plants to animals to humans.
- Can be shifted by travel (jet lag), shift work, or changes in routine, but prefers regularity.
- Not exactly 24 hours: The intrinsic period of the human clock averages about 24.2 hours — slightly longer than a day. Without external cues to reset it (a state called free-running), the clock drifts later each day. This is precisely why daily time cues matter so much.
- Loves consistency. It can adapt to almost any schedule — even a “night owl” one — provided the schedule is regular.
- Morning sunlight triggers a rise in cortisol, helping you feel alert and awake.
- Body temperature drops to its lowest point (temperature minimum) a few hours before waking, then rises through the day.
- Melatonin (the sleep hormone) increases in the evening as it gets dark, signaling the body to prepare for sleep.
- Adenosine builds up during wakefulness, creating sleep pressure, and is cleared during sleep.
