About fatigue

Fatigue is mental or physical exhaustion that stops a person from being able to function normally. However, fatigue is more than just feeling tired or drowsy - it is normal to become tired through physical or mental effort.

Causes of fatigue
Circadian rhythms
Fatigue and sleep
Causes of sleep loss

Causes of fatigue

Fatigue is caused by prolonged periods of physical and/or mental exertion without enough time to rest and recover. The level of fatigue varies, and depends on the following:

Workload;
Length of the shift;
Previous hours and days worked; and
Time of day or night worked.

Fatigue is associated with the following:

Spending long periods of time awake;
Obtaining an inadequate amount of sleep over an extended period; and
Obtaining an insufficient quality of sleep over an extended period.

Fatigue significantly affects a person's ability to function and the effects of fatigue include decreasing performance and productivity, and increasing the potential for incidents and injuries to occur.

Circadian rhythms

Circadian rhythms, or the internal body clock, are the body's natural rhythms that are repeated approximately every 24 hours.

Due to circadian rhythms, the human body is more awake during the day. The human body experiences a reduction in activity in the midnight to dawn period. This is a fundamental human characteristic and can not be changed.

Work schedules that require people to be awake and active at night, or to work for extended periods of time, disrupt circadian rhythms. These disruptions:

Affect the quality and quantity of sleep;
Affect task performance; and
May also contribute to a sense of personal dislocation and imbalance.

Accidents are more likely to occur at night, particularly during the period when the circadian cycle is at its lowest point (midnight to dawn) when a person would normally be sleeping.

Fatigue and sleep

Sleep is the only effective long-term counter-measure to fatigue. Maintaining sufficient levels of sleep will prevent fatigue.

The amount of sleep required by a person varies, with seven to eight hours of daily sleep considered the average for an adult. People who continually get less sleep than that necessary for them will accumulate a sleep debt.

For example, if a person who requires eight hours of sleep only has six hours of sleep, then this person is deprived of two hours of sleep. If this occurs over four consecutive nights, the person will have accumulated an eight hour sleep debt. Sleep debt leads to increased levels of fatigue.

Causes of sleep loss

A number of factors in the workplace and in a person's private life can cause sleep loss. Examples from the workplace include:

Extended working hours;
Irregular and unpredictable working hours;
Time of day when work is performed and sleep obtained;
Shift work;
Having more than one job; and
Stress.

Sleep loss may also be caused by health conditions such as obstructive sleep apnoea which is a condition which occurs while sleeping, where the muscles of the throat relax and block the airway above the voice box. This causes breathing to stop until the brain registers a lack of breathing and sends a small wake-up call, which briefly wakes the sleeper before they drift immediately back to sleep (usually the sleeper is not aware of having woken up). This process can repeat itself many times through the night, causing a person to feel fatigued during the day.

Many workers rely on caffeinated drinks, such as coffee to assist them to manage fatigue. However these will contribute to sleep loss if used within six hours before sleep. This effect may be increased if combined with medications containing ingredients such as pseudoephedrine hydrochloride.