Focus on Fatigue

Focus on Fatigue, Issue 33: Life is all about rhythm

By July 1, 2015 No Comments

Welcome to Focus on Fatigue,

The three o’clock slump is a term that most people are familiar with. It’s that hour or so in the mid-afternoon where we’d like nothing better than to lie down and have a nap. This urge is such a common part of the human experience that in some areas of the world the opportunity for people to take a short nap, or siesta, is part of the very fabric of the local culture.

This month we’ll look at the reason for these dips in energy and how they affect not just our afternoons, but our entire lives.

The FRMS Team

InterDynamics - Navigating Complexity. Delivering Clarity.

InterDynamics Pty Ltd
320 Adelaide Street Brisbane Qld 4000
Tel +61 7 32298300

Views expressed in articles and links provided are those of the individual authors, and do not necessarily represent the views of InterDynamics (except where directly attributed).

Feature Article

Life is all about Rhythm (the Circadian Rhythm that is!)

From a purely logical standpoint it would make sense if all humans woke up with maximum energy and then experienced a steady decrease in energy as the hours of wakefulness increased. We would grow sleepier and sleepier as time went on, until finally we were unable to stay awake. In reality, however, our sleepiness and our energy levels are regulated by two main processes:

  1. Sleep/wake homeostasis; and
  2. Circadian rhythm.

It starts with a little homeostasis…

When we’ve been awake too long it’s our sleep/wake homeostasis that tells us it’s time to sleep. It also helps us stay asleep until we’ve fully recovered from our period of wakefulness. If our sleep/wake homeostasis was the only thing in charge of our sleep then we would, indeed, experience a direct correlation between increase in hours awake and increase in sleepiness. The rising and setting of the sun would make no difference, and we would be able to reliably predict when we would be most alert no matter the time of day.

If only life was that simple!

…and then we add some rhythm

In reality, we have an internal clock (known as the Circadian Biological Clock) which knows exactly what time of the day or night it is. This clock has a very strong opinion about whether or not we should be awake or asleep. It is responsible for the rises and dips of wakefulness and sleepiness we experience throughout the day, known as our Circadian Rhythm.

As adults our sleep drive is usually strongest between two and four o’clock in the morning, and between one and three o’clock in the afternoon. This can be different for different people, depending on if you’re a “morning person” or an “evening person”. If we are well-rested the urge to sleep at these times won’t be as intense as it will be if we are sleep deprived.

Our circadian biological clock is regulated to a large degree by a part of the brain called the Suprachiasmatic Nucleus (SCN). This is a group of cells in the hypothalamus that respond to light and dark signals. In the morning the sun comes up and the light travels to the SCN and sets off a whole host of reactions that tell us it’s time to wake up. This includes adjusting our hormones and raising our body temperature. In the evening, when the sun goes down, our body reacts again. Except this time it’s telling us that it’s time to be sleepy.

If you want to stay awake during the day and sleep at night this is the perfect process. However, if you need to get your sleep during the day in order to work the night shift, it’s going to cause problems.

What sort of problems?

Niu and colleagues (2011) found that the consequences of disruption to the circadian rhythm include disruption of sleep, decreased vigilance, a general feeling of malaise, and decreased mental efficiency. They also found that shift workers who sleep during the day secreted more of a hormone called cortisol, which diminishes the healing power of sleep. Finally, these shift workers slept one to four hours less, on average, than night sleepers.

Another study (Ferguson, Kennaway, et. al.), conducted in 2012, looked at the sleep habits of 29 operators at a live-in mining operation who worked a seven-day, seven-night shift pattern. These researchers wanted to know if the circadian rhythms of these miners would adjust to the different sleep times. They found no real evidence of an adjustment to the workers’ circadian rhythms. Although, in this study, there were no changes in the amount of sleep they got, there was a significant decrease in their reaction times across that day-shift, night-shift period. This suggestions that the idea that our bodies will ‘just get used to it’ is not necessarily the case.

It has been concluded that: “Disturbed circadian rhythm in humans has been associated with a variety of mental and physical disorders and may negatively impact on work safety, performance, and productivity.” (Niu, et. al, 2011, p. 68)

What can we do about it?

Shift work causes us to live out of sync with our circadian rhythm, which can result in serious disruption to our sleep patterns. There are some behaviours shift workers can use in their attempts to minimise this disruption, such as:

  • Light exposure – Exposure to bright light will increase alertness while avoidance of light is recommended in the lead up to sleep
  • Strategic napping – Short naps can be beneficial in increasing alertness during a night shift and if they occur in the earlier part of the shift they are less likely to interfere with longer daytime sleep
  • Lifestyle choices – Regular exercise and a healthy diet increases the chances of achieving quality sleep


  • Akerstedt, T. and Wright, K. P. (2009) Sleep loss and fatigue in shift work and shift work disorder. Sleep Medicine Clinics, 4(2), 257-271.
  • Ferguson, S. A., Kennaway, D. J., Baker, A., Lamond, N. and Dawson, D. (2012) Sleep and circadian rhythms in mining operators: Limited evidence of adaptation to night shifts. Applied Ergonomics, 43(4), 695-701.
  • Kolla, B. P. and Auger, R. R. (2011) Jet lag and shift work sleep disorders: How to help reset the internal clock. Cleveland Clinic Journal of Medicine, 78(10), 675-684.
  • National Sleep Foundation. Sleep drive and your body clock. National Sleep Foundation. Accessed on: 9 August 2013.
  • Niu, S.-F., Chung, M.-H., Chen, C.-H., Hegney, D., O’Brien, A. and Chou, K.-R. (2011) The effect of shift rotation on employee cortisol profile, sleep quality, fatigue, and attention level: A systematic review. Journal of Nursing Research, 19(1), 68-81).

InterDynamics News

Conferences and presentations

This section outlines recent and upcoming InterDynamics speaking engagements and/or conferences that we recommend and will be attending.

Rail Crew Management and Timekeeping Conference, Omaha, 27th-29th May 2015

The 2015 Rail Crew Management and Timekeeping Conference was hosted by Union Pacific. It was held in Omaha from the 27th to the 29th of May.

InterDynamics and Norfolk Southern Corp jointly presented a new software product to improve fatigue management when deploying train crews to unscheduled train tasks.

The software, developed by InterDynamics is call the Assigned Services Planning Tool (ASPT) with Calling Windows.

Typically North American railroads deploy crew to trains on a first in – first out basis. After crews have had the required minimum rest they are added to a list of available crews and when they reach the top of the list they are deployed to the next train. As trains generally do not run to any schedule this leads to crews being uncertain when they will work and how best to manage their sleep.

The ASPT analyses a significant sample of past train running data to determine “windows” of time with a high likelihood of a train being available for “calling” a crew. These “calling windows” are then paired, from a home terminal to an away-from-home terminal and back. The paired windows are then used to create a roster or Assigned Service schedule.

Norfolk Southern intends to use the tool to assist them to create Assigned Service schedules that provide higher degrees of certainty, both of work periods and of non-work periods.

In the News

Article: SLU Researcher Discovers a Way to Control Internal Clocks

by Thomas Burris, Health Canal (1 June 2015)

In research published in Nature Communications, Thomas Burris, Ph.D., chair of pharmacological and physiological science at Saint Louis University, reports intriguing findings about a small molecule that directs the activity of key “clock proteins,” offering the potential to manage circadian rhythm and treat problems that are associated with its dysfunction, like sleep and anxiety disorders.

Video: Circadian Rhythm and Your Brain’s Clock

by SciShow (9 January 2014)

Why do we sleep at night instead of during the day? In this episode of SciShow Hank talks about circadian rhythms, how they work, and how they regulate different processes in our bodies. (This video is 4:09mins long)

Video: How Your Circadian Rhythm Tunes Your Health

by Satchin Panda, TEDxYouth, San Diego 2013 (11 February 2014)

Learn how your biological clock or circadian rhythm tunes physiology, metabolism and brain function. Dr. Satchin Panda’s research shows thousands of genes in every cell turn on and off at specific times of the day. This gene orchestra dictates the optimum times for everything from athletic performance, shaving, taking medicine to cramming for an exam. (This video is 11:19mins long. If you would like to skip the basic information already given in the previous video then start at 7:00 for interesting information regarding a study of meal timing in mice and how it affected their body composition)

In the Research

Article: Sleep loss and circadian disruption in shift work: Health burden and management

Rajaratnam, S. M. W., Howard, M. E. and Grunstein, R. R. (2013) Sleep loss and circadian disruption in shift work: Health burden and management. Medical Journal of America, 199, S11-S15.


About 1.5 million Australians are shift workers. Shift work is associated with adverse health, safety and performance outcomes. Circadian rhythm misalignment, inadequate and poor-quality sleep, and sleep disorders such as sleep apnoea, insomnia and shift work disorder (excessive sleepiness and/or insomnia temporally associated with the work schedule) contribute to these associations.

Falling asleep at work at least once a week occurs in 32%–36% of shift workers. Risk of occupational accidents is at least 60% higher for non-day shift workers. Shift  workers also have higher rates of cardiometabolic diseases and mood disturbances.

Road and workplace accidents related to excessive sleepiness, to which shift work is a significant contributor, are estimated to cost $71–$93 billion per annum in the United States.

There is growing evidence that understanding the interindividual variability in sleep–wake responses to shift work will help detect and manage workers vulnerable to the health consequences of shift work.

A range of approaches can be used to enhance alertness in shift workers, including screening and treating sleep disorders, melatonin treatment to promote sleep during the daytime, and avoidance of inappropriate use of sedatives and wakefulness-promoters such as modafinil and caffeine. Short naps, which minimise sleep inertia, are generally effective.

Shifting the circadian pacemaker with appropriately timed melatonin and/or bright light may be used to facilitate adjustment to a shift work schedule in some situations, such as a long sequence of night work.

It is important to manage the health risk of shift workers by minimising vascular risk factors through dietary and other lifestyle approaches.

Leave a Reply