Circadian management

Circadian management includes various ways to optimise one's circadian rhythm with respect to one's sleep schedule. The stability as well as the alignment of your circadian rhythm is critical to maintaining the quality of your sleep. However, depending on the timings of your sleeps and your scheduling restraints, you may or may not be able to sleep at optimal hours. To this end, it is possible to mitigate the effects of suboptimal sleep timings through shifting the circadian rhythm itself.

Circadian structure

Typical circadian timings of physiological processes

The circadian rhythm regulates a range of physiological processes that controls sleep-wake cycles. These rhythms are synchronized to local solar time (rather than clock time) when they are stabilised. In some regions, local clock time can differ substantially from the solar time, and additional consideration is required to correctly plan circadian management measures.

Those living in red regions should subtract hours from their clock time to get the solar time, and those living in green regions should add hours. The number of hours is to add can be seen according to the colour legend below.

Typical circadian markers

Local Solar Time	Marker	Note
21:00-00:00	SWS peak
01:00-03:00	Lowest alertness	Sleep is most favoured in this time
04:00-06:00	Min. body tempeturature	This may or may not be the time with the strongest subjective feeling of coldness
06:00-09:00	REM peak
09:00-11:00	Highest alertness
11:00-17:00	Daytime nap zone	This corresponds to the circadian dip in the early afternoon.
17:00-19:00	Max. body temperature

Methods

A variety of methods can be used to optimise one's circadian rhythm. For schedules that are close to optimal ones, relatively little intervention is needed, whereas for drastically shifted schedules, strict observance of below practices wil be required.

Circadian phase response curves to light and melatonin, with 0 defined to be the nadir of the circadian core temperature rhythm.
Source: Zhu, L., & Zee, P. C. (2012). Circadian rhythm sleep disorders. Neurologic clinics, 30(4), 1167–1191. https://doi.org/10.1016/j.ncl.2012.08.011

Light exposure prior to the temperature nadir results in a delay of circadian rhythms, whereas light exposure after the temperature nadir causes phase advances. Note that there is a dead zone in the middle of the day where bright light exposure has no effect on the timing of circadian rhythms. In contrast, melatonin administered in the beginning of the night advances the circadian rhythm, while melatonin in the morning delays the circadian rhythm. ]]

Dark period

Main article: Dark period

Dark period is a fixed daily period in which little or no melatonin-suppressing light should be allowed to enter the eyes. This is done because melatonin is essential to the stability of one's circadian rhythm. Blue, and to a lesser extent green light greatly suppresses and delays melatonin production. Left uncontrolled, this would significantly destabilise sleep and compromise its quality.

Using red- or orange-coloured laser goggles is the most common way to achieve this. For each schedule type, there is a set of recommended dark period timings, detailed in the napchart in schedule pages. It is also strongly recommended to avoid food intake and exercise in this period to align with the body's tendency to rest at night.

Those doing shifted schedules and those living near the poles may find the need to maintain dark period during daylight hours. This requires additional caution, as daylight is too strong to overcome with goggles alone. It is advised to stay indoors and use blackout curtains for this purpose.