Focus on Fatigue

Focus on Fatigue, Issue 29: The many faces of fatigue

By February 1, 2015 No Comments

Welcome to Focus on Fatigue.

It’s hard to believe it’s already February. Sometimes it can feel like life is rushing by and meeting all our various responsibilities – at work, at home and in the community – can be difficult. Fatigue can creep up on us when we are too busy to pay it much heed.

But when we talk about fatigue, what is it exactly that we’re talking about? This month we will explore the different types of fatigue and the ways in which they can affect our lives.

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 Article

The Many Faces of Fatigue

What is fatigue?

Fatigue has been described as ‘primarily a subjective experience that includes physiological performance decrements and psychological impairments such as decreased morale, judgment and mood.’ (Hossain, 2005)

So, we work hard and then we feel tired, or fatigued. When we are fatigued we are unable to work as hard or as well.

Physical fatigue versus mental fatigue

There are two main types of fatigue: physical fatigue and mental fatigue. In simple terms, these can be described as follows:

  • Physical fatigue – the longer we use our bodies to work hard the more tired we get and the harder it becomes to keep our bodies working at the same level.
  • Mental fatigue – the longer we use our minds to work hard the more tired we get and the harder it becomes to keep our minds working at the same level.

Physical fatigue and mental fatigue are caused by different types of exertion and have different effects on the body, right down to a biochemical level. However, they can and do influence each other in profound ways. For example, a mentally fatigued person will often get tired faster when doing a physical workout, than a person who is not mentally fatigued.

What about sleepiness?

Often, when we talk about fatigue, what we are actually referring to is sleepiness.

The terms ‘fatigue’ and ‘sleepiness’ have proven very difficult to define, and they are often used interchangeably. Indeed, even researchers will often make little or no attempt to differentiate between sleepiness and fatigue.

Fatigue that is related to sleepiness is affected by issues such as:

  • The length of time a person has been awake – the longer we stay awake, the more fatigued we will be
  • Circadian rhythm status – our circadian rhythm is a natural cycle that tells our bodies when to be awake and when to be asleep, it can be disrupted by changes to our sleeping pattern and the time of day we are sleeping (we will explore this important topic in greater detail in a more on this important topic in a future newsletter)
  • How likely we are to fall asleep – our drive to sleep will get stronger the longer we are awake until, finally, it becomes virtually impossible to resist sleep. This can be especially problematic if we fall asleep at an inappropriate time (eg. a driver falling asleep behind the wheel)

What’s the difference?

One of the biggest differences between exertion-related fatigue and sleepiness-related fatigue is that exertion-related fatigue (that is, physical and mental fatigue) can both be cured by rest. Once we have rested we can continue working.

However, there is only one cure for sleepiness-related fatigue. That is, of course, sleep! It is possible to increase our alertness through the use of strategies such as consuming water, coffee or healthy snacks, doing some light exercise or going for a walk. However, the need to sleep will catch up with us all eventually.

What does this mean for shift workers?

There is one particular situation where sleepiness and fatigue are likely to coincide on a regular basis: shift work! Shift workers are constantly striving to achieve adequate amounts of sleep and rest so that they are able to perform at their best both physically and mentally.

Here at InterDynamics, we follow the researchers lead and use the term ‘fatigue’ to refer to all of three types: physical fatigue, mental fatigue and sleepiness. However, there is a stronger focus on fatigue involving sleepiness.

In the months to come, as we examine more areas of fatigue, it will be important to keep in mind the different types of fatigue that can be experienced in the workplace, and how each can affect the lives of shift workers.


  • Gawron, V. J., French, J., and Funke, D. (2001) An overview of fatigue. In: Hankcock, P. A. (Ed.) and Desmond, P. A. (Ed.) Stress, workload, and fatigue: Human factors in transportation, p. 581-595. Lawrence Erlbaum Associates Publishers: Mahwah, NJ, US.
  • Hossain, J. L., Ahmad, P., Reinish, L. W.Kayumov, L., Hossain, N. K. and Shapiro, C. M. (2005) Subjective fatigue and subjective sleepiness: Two independent consequences of sleep disorders? Journal of Sleep Research, 14, 245-253.
  • Marcora, S. M., Staiano, W. and Manning, V. (2009) Mental fatigue impairs physical performance in humans. Journal of Applied Physiology, 106, 857-864.
  • Merkelbach, S. and Schulz, H. (2006) What have fatigue and sleepiness in common? Journal of Sleep Research, 15, 105-106.
  • Neu, D., Mairesse, O., Hoffmann, G., Valsamis, J., Verbanck, P., Linkowski, P. and Le Bon, O. (2010) Do ‘sleepy’ and ‘tired’ go together? Rasch analysis of the relationships between sleepiness, fatigue and nonrestorative sleep complaints in a nonclinical population sample. Methods in Neuroepidemiology, 35, 1-11.
  • Nozaki, S., Tanaka, M., Mizuno, K., Ataka, S., Mizuma, H., Tahara, T., Sugino, T., Shirai, T., Eguchi, A., Okuyama, K., Yoshida, K., Kajimoto, Y., Kuratsune, H., Kajimoto, O., and Watanabe, Y. (2009) Mental and physical fatigue-related biochemical alterations. Nutrition, 25(1), 51-57.
  • Shen, J., Botly, L. C. P., Chung, S. A., Gibbs, A. L., Sabanadzovic, S. and Shapiro, C. M. (2006) Fatigue and shift work. Journal of Sleep Research, 15, 1-5.

InterDynamics News

Conferences and presentations

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

9th International Conference on Managing Fatigue, Freemantle Western Australia, 23-26 March 2015

The ‘Managing Fatigue’ conference series is now an established and respected forum for research updates and discussion in the fatigue management community. First convened in 1992 by Associate Professor Laurence Hartley the meeting was most recently held in Freemantle in 2011. Each conference has primarily focused on the effects of fatigue in the transportation sector and this has involved working in conjunction with organisations such as the ‘National Road Transport Commission’ (NRTC) and the ‘Australian Transport Safety Bureau’ (ATSB). Over the years the meeting focus has also evolved to encompass a wider arena including sectors such as Aviation, Maritime, Industrial, Resources and Health.

Conference Themes:  Transportation, Resources, and Health

Who Should Attend?:  Occupational Health and Safety Professionals,  Transportation Staff, Researchers, Road Safety Experts, Military Personnel, Aviation Experts, Freight and Heavy Vehicle Professionals, Defence, Science and Technology Organisations, Medical Professionals, and Road Authorities

FRMS Forum Conference, Luxembourg, 6th-7th May 2015

The 2015 Conference will take place in collaboration with the Ministry of Transport, CAA and the airlines & employee groups of Luxembourg at the Double Tree Hilton in Luxembourg on 6th and 7th May 2015.

The FRMS Forum are pleased to hold their next meeting in Luxembourg following the kind invitation from  a representative of all stakeholders in that country.

The agenda for this meeting will cover:

  • Developments within the regulatory environment with specific focus on those from Europe
  • Experiences from operators who are implementing FRMS
  • Workshops to achieve a consensus on some of the issues facing regualtors, operators and employee groups that are emerging as FRMS is adopted.

The content will be developed in the following months but please reserve the dates in your diary.

On the 5th May, a short training session on the basics of FRMS will be held for those new to FRMS to have a good basic understanding of the main principles for implementing FRMS within their organisations.

For more information please visit the FRMS Forum website.

In the News

This news article shows how one type of fatigue can have a detrimental effect on our experience of other types of fatigue.

Interdependence of different types of fatigue

Too much work proves tiring despite good sleep

Ed Susman, MedPage Today, “Too much work proves tiring despite good sleep” ( February 2013

Workers with a heavier cognitive workload experience fatigue and sleepiness regardless of how much rest they actually get, researchers reported.



Following is the abstract of one of the research articles used in the development of this month’s Feature Article. It discusses the idea that fatigue and sleepiness are distinct but related concepts.

Neu, D., Mairesse, O., Hoffmann, G., Valsamis, J., Verbanck, P., Linkowski, P. and Le Bon, O. (2010) Do ‘sleepy’ and ‘tired’ go together? Rasch analysis of the relationships between sleepiness, fatigue and nonrestorative sleep complaints in a nonclinical population sample. Methods in Neuroepidemiology, 35, 1-11.

Objective: The lack of distinction in the clinical use of terms like fatigue and sleepiness is an important issue. While both fatigue and sleepiness can potentially be associated with nonrestorative sleep (NRS) complaints, their relationships are still poorly described. We propose to use Rasch analysis-based methods to study the interrelations of fatigue, sleepiness and NRS.

Methods:150 subjects (mean age = 39.3 years, range = 18–65) from a community sample underwent a structured computer-assisted web interview. We assessed demographic data, sleep habits, and subjective fatigue with the Fatigue Severity Scale (FSS), global and situational sleepiness with the Epworth Sleepiness (ESS) and the Stanford Sleepiness Scales, respectively, and affective symptoms with the Hospital Anxiety and Depression Scale. Dimensionality, measurement invariance and common person equating were investigated to study the FSS, ESS and their relations to NRS.

Results: NRS was linked to shorter habitual sleep duration and to higher scores on psychometric scales. Both sleepiness and daytime fatigue were positively correlated to each other and to the intensity of affective symptoms. Rasch analyses showed both the ESS and FSS to measure unidimensional concepts of sleepiness and fatigue, respectively. In contrast to the FSS, the ESS only showed partial invariance to an NRS complaint. Common person equating suggests that, despite similar Rasch-derived agreeability scores, fatigue and sleepiness (as measured by the FSS and ESS) nevertheless designate distinct constructs.

Conclusion: NRS complaints can simultaneously present with higher daytime fatigue and sleepiness levels but the associative relationships between fatigue and sleepiness remain relatively unaffected by NRS. Although participants might not present adequate differentiation, fatigue and sleepiness seem to relate to different underlying concepts.

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