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The Thinking Cap


Shift Worker Fatigue - Disturbing your Circadian Rhythm

Article prepared: 20 March 2013

Interest in the effects of shift work on employees has increased as it has become a common feature across many work fields including the health and resource sectors. Shift work affects health and performance by disrupting circadian rhythms and causing numerous alterations in human behaviour and physiology. Disturbing our natural circadian rhythms can have serious implications for both the brain and body. The levels of fatigue experienced by shift workers can be attributed to this disturbance.

The Circadian Rhythm

Our circadian rhythm is effectively an internal clock that drives our levels of alertness throughout the day, and interestingly, is wound by Earth’s rotation. The 24-hour cycle, tied to one turn of the planet on its axis, creates an internal biological clock mimicked by timepieces invented to measure the day (Cromie, 1999). These circadian rhythms are important in determining our sleep patterns. The body’s master clock that controls our circadian rhythms consists of a group of nerve cells in the brain called the suprachiasmatic nucleus, or SCN. The master clock controls the production of melatonin, a hormone that makes you sleepy. Since it is located just above the optic nerves, which relay information from the eyes to the brain, the SCN receives information about incoming light. When there is less light—at night for example—the SCN tells the brain to make more melatonin to make you drowsy. As light is the main signal influencing our circadian rhythms, it contributes to a release of hormones that control our internal clocks.

Disturbing Your Circadian Rhythm

When it comes to sleeping, our circadian rhythm determines that most of us tend to be asleep by midnight, wake near dawn, and stay awake throughout the day, which means that not all times of the day are favourable for sleeping. There are “forbidden zones” for sleep between 8am-12noon and 5pm-9pm where it can be more difficult to get to sleep (Wood, 2012). Furthermore, alertness and capability vary with the time of day, with two low points occurring between the zones of 3am and 5am, and again between 3pm and 5pm.

Given our natural tendencies to sleep at particular times and stay awake at other times, it is no surprise that shift work has a significant impact on workers circadian rhythms. Shift work causes the de-synchronisation of our work and sleep patterns with these different “zones”. Such de-synchrony leads to reduced alertness, increased experiences of fatigue, mood changes, gastric problems and disturbances in eating habits which can contribute to weight gain (M.Gibbs, 2005). Research indicates that the degree of fatigue that shift-workers encounter depends on the schedule that is being worked, but is generally most severe on night shifts and during shifts that start early in the morning (Turek, 2004). Research has also found that, compared with day shifts, evening and night shifts are associated with higher health and safety risks and reduced productivity. These findings are all during times when our circadian rhythms are telling our bodies to be asleep. When we are not doing this, we are not giving our body appropriate time to rest and restore itself – thus increasing our chances of experiencing high levels of fatigue.

Tips for Managing Fatigue in Shift Workers

The following are some tips for optimising roster or shift schedules to help manage the fatigue of workers:

  • Direct the rotation of shifts forward (morning/afternoon/night) as the body can adapt to going to bed later as opposed to earlier and there is more rest between shifts.
  • For shift changes, a faster rotation of 2-3 days may minimise sleep debt accrued from working long stretches of night shift and causes the least amount of body clock adjustment.
  • Roster design should take into account that individuals require at least 7-8 hours sleep per 24 hour period.
  • The finishing time of night shifts should be planned to avoid heavy traffic periods in order to minimise the likelihood of accidents (Minesafe, 2006).
  • Shift starts should be avoided between midnight and 6am to ensure adequate rest.
  • Determine shift length based on the mental and physical load of the job. For example, where work pressure is high, shorter shifts may be preferable over the standard eight our shift.

PSB Solutions’ Fatigue Management Programs

PSB Solutions provides Fatigue Management training that is informed by the latest research in psychology. PSB Solutions have Fatigue Management programs aimed at non-supervisory employee levels, as well as at supervisors and above.

If you would like to know more about how your employees’ fatigue can be better managed, or about PSB Solutions’ Fatigue Management services please call us on (08) 9489 3900 or email us – we’re here to help.


Cromie, W. J. (1999, July 15). Human Biological Clock Set Back an Hour. The Harvard Gazette.

M.Gibbs, S. H. (2005). Effect of shift schedule on offshore shiftworkers' circadian rhythm and health. Guildford: The University of Surrey.

Minesafe. (2006). Hours of Work and Fatigue.

Turek, F. W. (2004). Melatonin, sleep, and circadian rhythms: rationale for development of specific melatonin agents. Sleep Medicine, 523-532.

Wood, H. (2012). Fatigue and its Relationship to Roster Cycle Length. Australian Pipeline Industry Association. TMS Consulting.


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