NIOSH Training for Nurses on Shift Work and Long Work Hours

Circadian Rhythms That Promote Wakefulness

Figure 2.5 is a simple version of the rise and fall of circadian rhythms that promote wakefulness across the 24-hour day. A peak in wakefulness occurs in the evening a few hours before usual bedtime for a person on a normal, daytime activity schedule. This can be experienced as enhanced alertness in the early evening, even after being awake for long periods. The evening peak in alertness makes it difficult to go to bed earlier; sleep researchers call this time the “wake maintenance zone.” The circadian pacemaker gets us ready for sleep by reducing the wakefulness process before the expected bedtime, which promotes sleepiness and sleep onset.