Physiology of Fatigue

Shift workers, especially those on the night shift, and those driving during night-time hours are particularly vulnerable to fatigue. Because of the body’s circadian rhythm, time of day has a profound impact on fatigue.

Shift work

• People are physiologically programmed to sleep at night and be awake and active during the day. This can lead to a decrease the quantity and quality of sleep causing fatigue.

  (Akerstedt et al., 2008; Czeisler, 2015; Lerman et al., 2012; Matheson et al., 2014; Rosa & Colligan, 1997; Smith & Eastman, 2012)

• Employees on rotating shifts are less likely to adapt to the night shift which leads to sleepiness and fatigue. If a rotating shift is necessary, forward rotating shift is best.

  (Dall’Ora et. al, 2016)

• Night-shift workers’ do not get as much sleep during their time off as daytime or evening workers. Over several consecutive night shifts, fatigue can build up and result in poor performance on the job.

  (Baulk et al., 2009; Caruso, 2014; Folkard & Lombardi, 2006; Folkard & Tucker, 2003; Mitler et al., 1997; Park et al., 2000; Rosa & Colligan, 1997; Vallières et al., 2014; Van Dongen et al., 2003)

Night time driving

• Drowsy driving crashes typically occur during nighttime and early morning hours.

  (Akerstadt et al., 2001; Connor et al.,2002; Folkard et al., 1997; Keall et al, 2005; Lenne et al., 1997)

Time awake

• The physiological need for sleep goes up with time awake and goes down with time asleep.

  (Colten & Altevogt, 2006; Dinges et al., 2005)

Shift work

• Shift workers have a higher prevalence of short sleep duration compared to daytime workers.

  (Yong, Jia & Calvert, 2016)

Long hours or overtime

• Working long shifts can cause fatigue and affect performance due to the body’s increased need to sleep.

  (Akerstedt & Wright, 2009; Caruso, 2014; Caruso et al., 2004; Dall’Ora, 2016; Dembe et al., 2005; Philibert, 2005; Pilcher & Huffcutt, 1996)

Humans require adequate sleep (7-9 hours for adults) in order to function. Sleep debt, a cause of fatigue, happens when a person loses a sufficient amount of sleep or stays awake for an increasing period of time.

• Sleep deprivation can accumulate, and large sleep debt may result in chronic fatigue.

  (Edell-Gustafsson et al., 2002; Fletcher et al., 2003; Natale et al., 2003; Purnell et al., 2002)

Sleep Problems

• Sleep disorders, chronic diseases and medications can decrease sleep quantity and quality, increasing fatigue.

  (Smolensky et al. 2011)

• Research shows roughly 60% of shift workers complain about sleep loss and sleeping problems.

  (Edell- Gustafsson et al., 2002; Fletcher et al., 2003; Muecke, 2005; Natale et al., 2003; Purnell et al., 2002)

• Sleep deprivation in combination with working at night may further exacerbate the adverse effects of fatigue.

  (Akerstedt, 2003; Cohen et al., 2010; Santhi et al., 2007; Wright et al., 2013)

• Approximately 23% of working Americans suffer from insomnia.

  (Kessler et. al, 2011)

Individuals will experience fatigue the longer they conduct a specific task. This fatigue can manifest as sleepiness, muscle tiredness or mental tiredness.

• A person’s ability to remain focused on simple and repetitive tasks is limited. Examples are long-haul driving, working on an assembly line, baggage screening, scanning, inspections, quality control, etc.

  (Langner & Eickhoff, 2014; Matthews & Desmond, 2002)

• The "time-on-task effect " is the gradual increase in the amount of effort required to maintain the same level of performance on a task over time. In other words, the longer we are required to perform a tedious task, the more our attention, speed, and accuracy decline.

  (Grier et al., 2003; Szalma et al., 2004; Van Dongen et al., 2017; Warm et al., 2008)

• Time-on-task fatigue becomes worse as a result of extended wakefulness, night work, or both.

  (Basner et al., 2008; Doran et al., 2001; Gunzelmann et al., 2010; Lim & Dinges, 2008; Wesensten et al., 2004; Wickens et al., 2015)

• Research shows optimal duration for safe highway driving is under 90 minutes before sleepiness and time-on-task related decreases in performance can occur.

  (Ting et.al, 2008)

Some individuals are more prone to fatigue than others. Personal factors such as age or medical conditions can play a role.

• Some studies show that people over 40 years old have a harder time adjusting to night shifts due to circadian rhythm.

  (Harma et al., 2002; Learhart 2000; Fletcher et al. 2003; Muecke et. al, 2005; Poissonnet & Veron 2000, Reid & Dawson 2001)

• Sleeping disorders, including insomnia and sleep apnea, are associated with reduced safety and productivity in the workplace and increased risk of traffic incidents.

  (Horstmann et al., 2000; Howard et. al, 2004; Kucharczyk et. al, 2012; Mulgrew et al., 2008; Terán-Santos et al., 1999; Uehli et. al, 2014)

• Other sleep disorders affecting sleep quality (e.g., narcolepsy, restless legs syndrome) and chronic health conditions (e.g., asthma, chronic obstructive pulmonary disease, allergic and non-allergic rhinitis, rheumatoid arthritis, osteoarthritis, chronic fatigue syndrome) may further exacerbate the level of performance impairment associated with fatigue.

  (Droogleever et al., 2012; Fossey et al., 2004; Ohayon & Roth, 2002; Power et al., 2008; Pretto & McDonald, 2008; Schneider et al., 2004; Smolensky et al., 2007; Smolensky et al, 2011; Thorpy & Krieger, 2014)

• Other personal factors that may contribute to fatigue include; gender, socioeconomic factors, physical and mental health, endurance, genetic predisposition, need for sleep, diet and nutrition, physical activity level, body mass index, personality traits, substance use, medication use, family and marital status, job status, fatigue awareness.

Some jobs are more prone to fatigue due to task-related factors, environmental factors and organizational factors.

Task-related Factors

• The type of task an employee does can affect his or her level of fatigue including; the physical and mental demands of the task as well as an employee’s level of experience with the task.

Environmental Factors

• Characteristics of the work environment may contribute to the occurrence of fatigue. Some factors known to increase the risk of fatigue among workers are noise and poor indoor air quality. On the other hand, exposure to bright light has been shown to increase alertness and reduce fatigue.

  (Bengtsson et al., 2004; Bernstein et al., 2008; Buelow, 2001; Foret et al., 1998; Hawes et al., 2012; Jahncke & Halin, 2012; Kjellberg et al., 1996; Kjellberg et al., 1998; Kristiansen et al., 2014; Mills et al., 2007; Melamed & Bruhis, 1996; Nishihara et al., 2014; Reijula & Sundman-Digert, 2004; Saremi et al, 2008; Smolders & de Kort, 2014; Tanabe & Nishihara, 2004; Wyon, 2004)

Organizational Factors

• Organizational factors like safety culture, employee engagement, leadership commitment and supervisor support can help prevent fatigue-related incidents. Other factors that can affect employee fatigue are; company size, type of industry, absence of a fatigue risk management system, work scheduling policies, and employee compensation (payment by task, hour or overtime).

Fatigue caused by time of day, sleep debt and time on task have several detrimental effects:

• An individual will experience a decrease in their ability to perform basic cognitive functions resulting in a decline in a number of vital activities such as attention, vigilance and memory.
• Decreases in cognitive performance lead to a decline in job and safety performance. An individual will become less productive thus increasing their risk of a negative safety incident.
• A chronically fatigued individual will become more at-risk to health problems like cancer and heart disease. Research has demonstrated that fatigued individuals are an economic strain to themselves, employers and society due to decrease productivity, increased risk of negative safety outcomes, and increased illness.

• Extensive research has shown that fatigue, as a result of shift work and sleep deprivation, leads to decreases in cognitive performance, short-term memory, concentration, performance speed, reaction time, executive function, psychomotor activity, attention, vigilance, alertness, accuracy, mathematical calculation and judgment.

  (Akerstedt et al., 2001; Balkin et al., 2000; Balkin et al., 2004; Belenky et al., 2003; Dall’Ora et al., 2016; Dinges et al., 1997; Dorrian et al., 2005; Drummond et al., 2000; Drummond et al., 1999; Drummond and Brown, 2001; Fairclough and Graham, 1999; Griffiths et al., 2014; Niu, 2011; Philip et al., 2003; Philip et al., 1997; Roehrs et. al, 2003; Stenuit and Kerkhofs, 2008; Williamson et al., 2011)

• Three of the most well-documented detriments of fatigue are decreases in attention, vigilance, and memory performance.

  (Akerstedt et al., 2001; Amendola et. al, 2011; Arnedt et al., 2005; Balkin et al., 2000; Dinges et al., 1997; Dingley, 1996; Dorrian et al., 2005; Drummond and Brown, 2001; Gillberg et al., 1994; Niu et. al, 2011; Philip et al., 1997; Roehrs et. al, 2003; Rosekind et. al, 2010; Rouch, Wild, Ansiau, & Marquie, 2005; Seki & Yamazaki, 2006; Valdez et al., 2005; Wyatt et al., 1999)

• Research shows night shift workers experience disruptions in cortisol and melatonin, affecting their sleep quality and increasing their fatigue.

  (Kudielka, Buchtal, Uhde, & Wust, 2007; Niu, 2011)

• Losing small amounts of sleep over time can be detrimental. A person who sleeps 6 hours a night for 2 weeks performs similarly to someone who loses one full night of sleep.

  (Van Dongen et al., 2003)

Work performance, including productivity, decreases as employees become fatigued. Fatigue-related decreases in work performance have been observed in those on shift work, rotating shifts, night shift, early start times, working overtime or long hours, and employees with sleeping problems.

• Work performance, including productivity, decreases as employees become fatigued.

  (Caruso et al., 2015; Dall’Ora et al., 2016; Drake et al., 2001; Kucharczyk et al., 2012; Pilcher et al., 1996; Rosekind et al., 2010)

• Worker productivity decreases between 6% to 2.5% depending on level of tired or sleepiness. (Rosekind et. al, 2010)
• Declining work performance from fatigue has been observed in those on shift work, night shift, rotating shift, working overtime or long hours, sustained time on task and employees with sleeping problems.

  (Barker and Nussbaum, 2011; Caruso et al., 2016; Dall’Ora et. al, 2016; Griffiths et al., 2014; Landrigan et. al, 2004; Lockley et. al, 2004; Muecke et. al, 2005; Niu et. al, 2013; Olds and Clarke, 2010; Scott et. al, 2006; Rosekind et al., 2010)

Workplace safety performance decreases as employees become fatigued. Individuals working night shift, rotating shifts or long hours are at a higher risk for safety incidents.

(Ashford, 1998; Folkard and Tucker, 2003; Folkard and Lombardi, 2006; Niu et. al, 2001; Swaen et al., 2003; Wagstaff et. al, 2011; Williamson et al., 2011)

Sleeping Disorders

• Poor sleep is a strong predictor of negative workplace safety incidents. Individuals with sleeping disorders, such as insomnia or obstructive sleep apnea are more likely to be involved in a negative workplace safety incident.

  (Åkerstedt et al., 2002; Allen et al., 2007; Carter et al., 2003; Chau et a., 2008; Hetherington et al., 2006; Kecklund et al. 1999; Kucharczyk et. al, 2012; Lindberg et al., 2001; Melamed and Oksenberg, 2002; Philip & Akerstedt, 2006; Rosekind et. al, 2010; Ulfberg et al., 2000; Uehli et al., 2014; Wadsworth et al., 2006)

• Approximately 13% of work injuries could be attributed to sleep problems.

  (Uehli et. al, 2014)

Time of Day

• Numerous studies have shown a higher safety risk among night shift compared to day shift.

  (Ashford, 1998; Folkard, 1997; Folkard and Tucker, 2003; Folkard et. al, 2006; Swaen et al., 2003; Wagstaff et. al, 2011; Williamson et al., 2011)

• A nearly 30% increased risk of negative safety incidents happen during night shifts compared to morning shifts.

  (Folkard et al., 2006)

• Night shifter workers are 3 times more likely to be injured in a workplace incident compared to day shift workers.

  (Swaen et al., 2003)

• Several studies suggest rotating shifts may have a greater safety risk than non-rotating shifts due to synchronization.

  (Wagstaff et. al, 2011)

Long Hours

• Research shows safety risk increases with shift duration and number of hours worked per week.

  (Barger et al., 2005; Dall'Ora, 2016; Folkard et al, 2004; Folkard and Lombardi, 2006; Olds and Clarke, 2010; Wagstaff et. al, 2011)

• One study demonstrated a two-fold increase in safety risk in a 12-hour shift compared to an 8- hour shift.

  (Wagstaff et. al, 2011)

Traffic crashes

• Studies show fatigue is a contributing factor to traffic crashes.

  (Akerstedt et al., 2008; Barger et al., 2005; Connor et al., 2002; Craft, 2007; Cummings et al., 2001; Dobbie, 2002; Flatley et al., 2004; Hartenbaum et al., 2006; Horne and Reyner, 1995; Howard et al., 2004; Klauer et al., 2006; Lenne et al., 1997; Lyznicki et al., 1998; Nabi et al., 2006; Philip et al., 2001; Philip & Akerstedt, 2006; de Pinho et al., 2006; Stutts et al., 2003; Williamson et al., 2011)

• It is estimated that 19% of vehicle crashes are attributed to drowsy driving.

  (Connor et al., 2002)

• One study showed the odds of being in a crash or near crash were nearly 3 times higher when the driver was drowsy.

  (Klauer et al., 2006)

• Individuals suffering from sleeping disorders, such as sleep apnea, are at a high risk of traffic crashes.

  (George et al., 1999; Howard et al., 2004)

Fatigued individuals and shift workers are at a higher risk of health problems including, but not limited to, depression, cardiovascular disease, obesity and diabetes.

• Shift workers, those who work long hours and those who are sleep deprived, are at higher risk of vehicle crashes, obesity, psychological disorders such as anxiety and depression, musculoskeletal disorders, reproductive problems, diminished immune response and numerous chronic diseases including hypertension, cardiovascular disease, gastrointestinal disease, cancer, diabetes.

  (Caruoso et. al, 2016; Perkins et. al, 2001; Frazier et. al, 2003; Rosekind et. al, 2010; Rajaratnam et. al, 2011)

Research shows fatigue causes decreased productivity, reduced safety performance and poor health which can lead to increased costs to employers and society.

• Fatigue-related decreases in productivity costs employers between $3,156 and $1,293 per employee annually.

  (Rosekind et. al, 2010)

• Insomnia costs the U.S. economy more than $100 billion per year.

  (Wickwire et al., 2016)

• Employees with untreated sleeping disorders, such as insomnia, incur significantly greater direct and indirect health care costs.

  (Simon et. al, 1997)