Focus on Fatigue

Focus on Fatigue, Issue 32: Sleeping in stages

By June 1, 2015 No Comments

Welcome to Focus on Fatigue.

It’s June and winter has brought a decided chill to the air. Now is a great time to curl up in warm blankets and have a snooze. But how will we feel when we wake up? Will we feel refreshed and ready to start day? Will we be groggy and irritable? Will we have trouble resisting the urge to hit the snooze button, roll over and go back to sleep? Most importantly, can we do anything to improve our chances of waking up with ease?

This month we will be looking at the stages of sleep, including how they work and how they affect us.

The FRMS Team

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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 Articles

Sleeping in Stages

The stages of sleep were first described by Alfred Loomis and his colleagues in 1937. In this study, an electroencephalograph (EEG) was used to study the brain waves of 61 people while they slept. They discovered that people move through five distinct stages of sleep from the moment they fall asleep until the moment of waking. Since then, other researchers have sort to further understand and clarify these stages.

Today, researchers still measure brain waves when looking at the stages of sleep, but they also measure muscle tone and eye movement. These three measures together have given us a pretty good idea of how the stages of sleep work.

What are the stages of sleep?

In 2007, the American Association of Sleep Medicine (AASM) published the standards that are used for analysing the different stages of sleep. This publication reduced the number of stages to four, as described below:

  • N1 – A brief stage of light sleep in which the sleeper can easily be woken. This lasts about ten minutes
  • N2 – This is when your eyes stop moving and your muscles relax
  • N3 (previously divided into two stages) – This is deep sleep, or slow-wave sleep, in which the brain waves slow down. It is difficult to wake someone who is in deep sleep.
  • REM sleep – This is the place where dreams happen – literally. During this stage the brain paralyses many of the sleeper’s muscles to prevent the sleeper from acting out their dreams.

The movement through these stages is called a ‘sleep cycle’. When the cycle is complete the sleeper starts the cycle over. In an adult each cycle lasts about 90 to 110 minutes and repeats four to six times in a full night of sleep.

How do sleep cycles work?

When you first go to sleep you quickly descend through N1 and N2 until you reach N3, deep sleep. Then, after a while, you travel back up through N2 and N1 and enter REM sleep. This completes one cycle. You start a new sleep cycle when you begin to descend through the stages again.

As you continue through the night you spend less time in deep sleep and more time in REM sleep until finally you stop going into deep sleep altogether. This is around the time that you might start to wake up for brief periods before going back to sleep.

After about four to six cycles you will wake up naturally and not go back to sleep.

How can I work with my sleep cycles to wake up feeling refreshed?

Every time we are woken up by an outside influence, such as the buzzing of an alarm or the chirping of birds it interrupts our sleep cycle. Sometimes we are already in N1, a light sleep, and waking up feels natural. However, if we are in the deep sleep stage then waking up, and staying awake, really can be a struggle. This groggy feeling is called sleep inertia and we will talk about it more in a future newsletter.

While we can’t do too much about the chirping birds, we can try to time our alarms to coincide with our sleep cycles. Some experts recommend working out your ideal wake-up time by counting multiples of 90 minutes. For example, if you go to bed at 10:00pm, set your alarm for 5:30am (a total of 7½ hours of sleep). It may be necessary to play around with the timing to suit your individual sleep cycle length.

How are my sleep cycles affected if I don’t get enough sleep?

The important thing to remember here is that all sleep is not created equal! While each of the stages of sleep has benefits for the sleeper, the deep sleep and REM sleep stages are the most important. This is why short naps, while helpful in the short-term, will never eliminate the need for long periods of sleep. The body cannot get into deep sleep or REM sleep if it is not allowed to go through a full sleep cycle.

If you are sleep deprived then, when you do go to sleep, your body will automatically adjust your sleep cycles so that you can recover. If you haven’t had enough deep sleep then you will spend longer in deep sleep than you normally would. If you haven’t had enough REM sleep then this is where you will spend more time. If you’re deprived of both deep sleep and REM sleep then getting that extra deep sleep will be your body’s first priority.


  • Carskadon, M. A. and Dement, W. C. (2011) Normal human sleep: An overview. In: M. H. Kryger, T. Roth and W. C. Demend (Eds.), Principles and practice of sleep medicine, 5th Edition. Pp. 16-26). St. Louis: Elsevier Saunders.
  • Loomis, A. L., Harvey, E. N. and Hobart, G. A. (1937) Cerebral states during sleep, as studied by human brain potentials. Journal of Experimental Psychology, 21(2), 127-144.
  • American Association of Sleep Medicine (2007) The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. American Association of Sleep Medicine: Westchester, IL.
  • American Association of Sleep Medicine (2013) Sleep cycles. Sleep Education for School. Retrieved 13 June 2013 at

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: How to feel refreshed even after too little sleep – and why you MUST have an afternoon nap. Never wake up tired again

by Professor Richard Wiseman (24 March, 2014)

Insomnia is the modern malaise. But in a new book, Professor Richard Wiseman explains the simple techniques you can use to get the sleep you need. On Saturday, he revealed why some lucky individuals are ‘super-sleepers’. Today, he explains how you can become one, too . . .

Video: Sleep stages and circadian rhythms

by Carole Yue, The Khan Academy (27 February 2014)

Learn about the 4 main sleep stages and circadian rhythms. (This video is 7:56mins long)


The paper that started it all! Following is the Summary section of Alfred Loomis’ famous article that first attempted to described the stages of sleep.

Loomis, A. L., Harvey, E. N. and Hobart, G. A. (1937) Cerebral states during sleep, as studied by human brain potentials. Journal of Experiemental Psychology, 21(2), 127-144.

1. A new type of push-pull amplifier system, especially designed to record accurately the large slow potentials, is used to study the potential patterns of sleep.

2. Normal variability of different individuals are described together with the changes in potential pattern as a result of various influences.

3. Five state of sleep characterized by strikingly marked differences in potential can be recognized. They are A, alpha; B, low voltage; C, spindle; D, spindle and random; E, random; in order of appearance and in order of resistance to change by disturbances.

4. The ‘moment of sleep’ will depend on the criterion of ‘sleep.’ As sleep begins the record has the character of the A state.

5. Movements may occur without a change of state and a change of state without movement, but frequently movement is immediately followed by a change of state upward, occasionally downward, and occasionally a movement occurs just after a change of state.

6. During sleep there is a continual shift in states upward and downward sometimes associated with recognized stimuli, sometimes without any external stimulus but probably as a result of internal stimuli. Such changes are represented by graphs.

7. Stimuli shift the level upward sometimes skipping one or two states but not necessarily awakening the sleeper. Specific instances are described.

8. Dreams in two instances have occurred in the B state.

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