Workplace safety requires a systematic approach that includes an understanding of risk factors and identification of hazards. Worker fatigue has been identified as a risk factor for both acute and cumulative injuries. Research has shown that physically demanding work, characterized by forceful exertions, prolonged duration, repetitiveness, and their interactions, places high stresses on the body, which in the absence of rest can result in fatigue (Kumar 2001). Fatigue and incomplete recovery can lead to decreased capacity that can result in an increased risk of injury and a decline in work efficiency (Kumar 2001, de Looze, Bosch, and van Dieën 2009, Visser and van Dieën 2006). In addition, fatigue contributes to accidents, injuries and death (Williamson et al. 2011). For example, up to 20% of transportation accidents may be attributed to fatigue. Over $300 million in lost productivity time in US workplaces can be tied to fatigue. Significantly reducing the incidence of fatigue-induced workplace injuries and lost productivity depends on the accurate and timely detection of fatigue.

Although the term fatigue is commonly used, it has come to refer to many concepts in occupational safety and health. In order to manage and mitigate fatigue and the associated risks, it is essential to understand the different types and components. Fatigue is generally accepted as resulting in the impairment of capacity or performance as a result of work. However fatigue is multidimensional, either acute or chronic, whole body or muscle level, physical or mental, central or peripheral. In addition, it includes a decline in objective performance as well as perceptions of fatigue. Of added importance are the roles of sleep and circadian function. Each of these aspects of fatigue do not occur in isolation, but interact to modify worker capacity and injury risk. Both mental and physical fatigue can result in poor decision making, which may result in an acute injury (Williamson et al. 2011). The risk of injury is dependent on both the injury mechanism and the characteristics of the work being performed. Parameters of importance in the development of fatigue, and subsequent risk, include the length of time-on-task between breaks, work pace, and the timing of rest breaks (Williamson et al. 2011).

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