| Function | Typical Circadian Rhythm |
|---|
| Peak mental alertness and memory | Two daily peaks: around 9:00 a.m. and 9:00 p.m. |
| Lowest body temperature | About 97°F around 4:00 a.m. |
| Highest body temperature | About 99°F around 4:00 p.m. |
| Peak hearing, visual, taste, and smell sensitivity | Two daily peaks: around 3:00 a.m. and 6:00 p.m. |
| Lowest sensitivity to pain | Around 4:00 p.m. |
| Peak sensitivity to pain | Around 4:00 a.m. |
| Peak degree of sleepiness | Two daily peaks: around 3:00 a.m. and 3:00 p.m. |
| Peak melatonin hormone in blood | Between 1:00 a.m. and 3:00 a.m. |
| Sources: Information from Campbell (1997); Czeisler & Dijk (2001); Refinetti (2000); M. Young (2000). |