Fatigue Management

Awake Stage 1 Stage 2 Stage 3 Stage 4 REM (dreaming)
Figure 1. Brain Waves During Sleep
As can be seen in the traces of electrical wave activity in the human brain in
Figure 1, the progression from Stage 1 to the Deep Sleep Stages is
characterised by slower and larger wave activity. The smallest waves are
called Alpha waves (present when a person is relaxed and awake with eyes
closed), while the slow, large waves of Stage 4 sleep are called Delta waves.
Stage 1 is a transition state between wakefulness and sleep and is of short
duration (about 2-5 per cent of total sleep time). An adult normally spends
about 50 per cent of sleep in Stage 2, about 20-25 per cent in the deep sleep of
Stages 3 and 4, also called Slow Wave Sleep, and about 20-25 per cent in Rapid
Eye Movement (REM) sleep, where dreaming occurs. Typically, a sleep cycle
through all the stages lasts between 90 and 110 minutes, starting with Stage 2
(light sleep), proceeding through Stages 3 and 4 (deep sleep) and ending with
REM sleep (dreams). Further cycles then occur until waking. It is usually
progressively more difficult to awaken people as they pass from Stage 1 to the
deep sleep stages. Each person seems to have a unique pattern of transition
and duration through the stages.
The Importance of Deep Sleep. There is evidence that Stage 3 and 4 sleep,
the most common in the first few hours of sleep, serve the function of physical
and mental restoration. The amount of Stage 3 and 4 sleep can increase after
strenuous physical activity. Thus, you would expect fighting soldiers to spend
a little more than the normal proportion of sleep in deep sleep. Disturbances to
sleep, such as a loud noise, tend to interrupt the deeper sleep stages and take
the person back to lighter sleep stages. Soldiers sleeping in a noisy battlefield
are likely to get less deep sleep than they need to obtain maximum physical
and mental restoration.
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