This paper explores fatigue and its related effects on humans during work as well as normal daily activities of common people. Fatigue is certainly a challenge in today’s world since systems are near perfect and hardware/software issues are minimal compared to few years back. Today, the most frequent safety threat stems from the reality of occasional suboptimal human performance (Avers, K., & Johnson, W. 2011).  In todays 24/7 world, fatigue is associated with sleep loss, shift work, and long duty cycles. This review will summarize fatigue, its effects and countermeasures based on recent research and mitigation efforts. 

Human Fatigue

A Review

Fatigue is an important factor to consider in all industries and military fields in today’s 24/7 advanced lifestyle. Fatigue is generally associated with sleep loss and shift work. Fatigue can result in a person being inattentive, careless and inefficient (Caldwell, J. 1997). According to Air Force Research Laboratory (AFRL) and United States Air Force School of Aerospace Medicine (USAFSAM), fatigue is a threat to productivity and safety in variety of settings. Whether we are flying an aircraft, maintaining an aircraft or simply driving from home to work, fatigue can cause serious mishaps. It is estimated that fatigue-related problems cost America more than $18 billion a year in terms of lost productivity, and it is clear that fatigue-related drowsiness on the highways annually contributes to over 1500 fatalities, 100,000 crashes and 76,000 injuries (Military aviation fatigue countermeasures workshop, 2004). 

Fatigue is commonly referred to as sleepiness or a general tired feeling resulting from extended wakefulness, insufficient sleep, or circadian disruption (Dinges, 1995). However, fatigue is a multi-dimensional construct (Dodge, 1982) and this definition lacks the performance consequences associated with Fatigue (Avers, K & Johnson, W., 2011). So, fatigue is definitely more than being tired, sleepy or falling asleep. Fatigue is defined as a complex state that has physical, psychological, physiological, and emotional implications that can impact the safe performance of routine and non-routine work activities (Carskdon & Roth, 1991). 

There is evidence especially when it comes to aviation industry that proves fatigue has led to fatal mishaps in civilian and military aviation. Fatigue has been identified as contributing factor in 9.6% of all Air Force Class A mishaps over the past 30 years. Fatigue is also identified as causal in many civilian and commercial aviation caused by pilots, crew, and maintenance technicians. The U.S. National Transportation Safety Board (NTSB) has identified fatigue as a contributor factor in more than 300 fatalities in airline accidents (Nesthus & Avers, 2009; Rosekind, 2011). These incidents occurred at night or during mid-night shift, after consecutive extended duty days, sleep restriction or during time zone and shift changes. In 1993, crash of a DC-8 in Guantanamo Bay, Cuba is attributed to fatigue. Both Korean Air Flight 801 crashed killing 228 people and in 2002, American Airlines Flight 1420 was involved in a fatal crash had Fatigue as Causal factor. 

Fatigued driver is not a new news either. Fatigue and sleepiness at the wheel are well-know risk factors for traffic accidents (Connor et al., 2002), many drivers combine sleep deprivation and driving (Mitler et al., 1997). (Arnold et al., 1997) suggests that professional drivers engage in this dangerous behavior because of economic rewards and vacationers/casual drivers are impacted by socio-cultural factors. Medical workers (physicians, nurses, technicians) are also at risk of facing similar challenges in their work places (Lamberg, 2002). They have to stay awake for long hours and work under stressful situations. This can lead to sleep deprivation, fatigue and eventually a risk of professional errors becomes a stark reality (Gaba & Howard, 2002). However, this is not just a work safety issue but also a much broader traffic safety issue. Traffic accidents from work to home is one of the major causes of injury and deaths among workers (Personick & Mushinski, 1997). These incidents related to conflicts between physiological needs and social or professional activities make it important for us to understand the human limits of fatigue and sleep deprivation (Rajaratnam & Arendt, 2001). 

The key to understanding the detrimental effects of fatigue lie in differentiating between sleepiness and fatigue. People, generally are confused between fatigue and sleep. Even if their causes (heavy workload versus sleep deprivation) and counter-measures (rest versus sleep) are very different, people do not necessarily discriminate the effects and remedies to the two conditions. For example: sleep-deprived drivers will stop more frequently but will not necessarily sleep. Sleepiness is a difficulty in remaining awake while carrying out activities. If a person is awake for extended time and experiences a sleep restriction, he/she will experience increase sleep pressure and generate cumulative sleepiness. Sleepiness is related to circadian and homeostatic influences of our biological clock, which generates and maintains chrono-biological rhythms. These rhythms are responsible for controlling sleep and wakefulness and are also known as circadian rhythms. These rhythms are normal, inherent, unavoidable, 24-hr rhythms in human cognitive and physical performance and they oscillate between a high point late in the day to a low point in the pre-dawn hours with a peak-to-trough amplitude of about 5 to 10% of their average value (Woodrow, A. & Webb, J. 2011). In simple words, during daytime. Human rhythms generate a drop of vigilance in the mid-afternoon and a very alert period towards the end of the afternoon (Lavie, 1986). 

The fatigue related to disruption in circadian rhythms falls under two major categories. First, Fatigue or sleepiness associated with attempting to work at times that coincide with the circadian trough (drop in the rhythm). So, night shift workers will often experience this type of fatigue. Second, occurs when a person experiences a schedule change. For example: shift worker will experience this type of fatigue for several days/nights after rotating to a new schedule, also known as shift lag. And, travelers will experience this fatigue after traveling to a new time zone, also known as jet lag. This type of fatigue actually leads to loss of synchrony with external cues and the internal clock, which contributes to that feeling of malaise, when we are traveling. Based on these disruptions of our circadian rhythms, fatigue can build up normally and unavoidably within one waking period. This can be termed as acute fatigue and can resolved with a one good quality sleep period.  Acute fatigue can build up across several waking and duty periods when there is inadequate recovery, also known as cumulative fatigue. If cumulative fatigue episode is not resolved, chronic fatigue can set in after one to two week period. Chronic fatigue can have serious effects ranging from desire to sleep during duty, apathy, short-term memory impairment, concentration, body aches and malaise lasting more than 24 hrs. (Air Force Safety, 2011). 

We have to understand three main aspects of fatigue. Fatigue is ubiquitous (universal) which means it affects everybody at different levels. This can lead to misperception amongst people eventually leading to decision errors and safety related issues. Fatigue is pervasive, which means it affects everything we do, physically and cognitively. Fatigue is also insidious, which means its difficult for us to realize how fatigued we are or how badly we are performing? For example: we have all experienced attention lapses especially when we are driving long distances. It is also true that each person reacts to these three aspects of fatigue at different levels based on their age, health and endurance. And, understanding these aspects can make us aware of when to call time-out or take a break when conducting safety sensitive jobs – flying, driving, operating etc. 

Sleep loss and fatigue results in short-term and long-term ill effects of human body. Lack of sleep in the short term is associated with irritability, impatience, anxiety, and depression (Miller, C. 2001). In the long term, shift workers may experience stomach problems such as heart-burn and indigestion, menstrual irregularities, colds, flu, weight gain and cardiovascular problems than day workers (Miller, C. 2001). Shift workers are definitely at disadvantage here since human biology is not designed for nocturnal work. We cannot see well in the dark, our metabolism slows down overnight, pineal gland releases melatonin, which, in turn, makes us feel drowsy (Woodrow & Webb, 2011). So, the likelihood of us falling asleep, when comfortably lying down with closed eyes is higher compared to when we try sleeping during the day. Since, we are designed to work during the day and sleep at night, there is practically no “good” shift work schedule available. However, there are an infinite number of possible shift work schedules based on our understanding of associated risk and our appetite for risk taking. 

Sleep deprived people process information slowly and their reaction time slows down, resulting in mistakes and short-term memory issues. This can lower job productivity and can cause serious accidents. Folkard & Tucker, 2005 combined the results from numerous field studies to show the effects in term of safety and productivity. There data showed that risk of injuries and accidents was found to increase in an approximately linear fashion across the three shifts (18.3% on the afternoon shift; 30.4% on the night shift). Efficiency and accuracy measured between is 0700 – 1900 h is only above average and dramatically drops or is impaired during all other times especially during the early hours of the morning. Risk of workplace accidents and automobile incidents rises for tired shift workers, especially on the drive to and from work. 

A power nap is a best solution in these scenarios rather than taking the risk to drive. Studies show that listening to loud radio or opening car windows are temporary measures and should be taken as signal of fatigue and the need to pull over immediately (Taneja, N. 2007) Use of public transportation or companies providing carpool services is another viable option for shift workers. 

Finally, An organization whether commercial or government, should follow fatigue countermeasure guidelines and regulations to mitigate fatigue related issues at workplace. For example: scheduling good quality breaks, inserting naps, keeping duty periods short and scheduling no more than three night shifts in a row. Affording employees with uninterrupted 24 hr. rest after night shifts and scheduling days off in continuous periods of at least 3 days. An individual can follow general guidelines at a personal level such as by reducing stress, staying healthy with regular exercise and balanced diet, avoiding cigarettes and alcohol. Establishing a bed time routine, taking a warm bath before bedtime, avoiding noise and controlling light levels and temperature (approximately 70 F) in the bed room will also help an individual get a good quality 7 – 8 hr. of sleep. 

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