Definition

Time in the circadian body clock cycle when fatigue and sleepiness are greatest and people are least able to do mental or physical work. The WOCL occurs around the time of the daily low point in core body temperature - usually around 0200-0600 when a person is fully adapted to the local time zone. However, there is
individual variability in the exact timing of the WOCL.

Source: ICAO Fatigue Management Guide for ATS Provders

Description

The circadian body clock is one of two key processes that regulate sleep timing and quality (the other is the sleep homeostatic process, i.e. the body's need for deep sleep that builds up during waking and discharges during sleep). The circadian body clock has connections to sleep-promoting and wake-promoting centres in the brain, which it modulates to control the sleep/wake cycle.