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  Table of Contents 
Year : 2022  |  Volume : 26  |  Issue : 4  |  Page : 225-229

The effect of sleep quality and mental fatigue on the learning rate of shift workers with fast shift work rotation

Department of Occupational Health Engineering, Faculty of Health, Isfahan University of Medical Sciences, Isfahan, Iran

Date of Submission01-Nov-2020
Date of Decision04-Apr-2021
Date of Acceptance12-Jul-2021
Date of Web Publication24-Dec-2022

Correspondence Address:
Dr. Ismail Shokrolahi
Department of Occupational Health Engineering, Faculty of Health, Isfahan University of Medical Sciences, Isfahan
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijoem.ijoem_439_20

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Background: Modern industrial societies are always prone to errors and accidents due to complex devices, multitasking, and shift work jobs. Therefore, behavioral tests in learning and memory are necessary to evaluate employees' perceptions to examine the brain's information processing and the physiological and psychological aspects of memory disorders. Materials and Methods: In this study, the effect of fast shift rotation, sleep quality, and mental fatigue on individuals' learning and memory was investigated using a maze device. Participants were divided into two groups (regular daytime workers and shift workers). The quality of sleep was assessed using the Pittsburgh Sleep Quality Index (PSQI), and the rate of mental fatigue was evaluated using a checklist published by the Japan Industrial Safety and Health Association. Results: Learning time and the number of learning errors at the beginning and end of the morning shifts and night shifts had a significant relationship (P value <0.0001). However, there was no meaningful relationship between sleep quality and time and the number of learning errors in day workers and shift workers. Conclusion: The results indicated that although shift workers experience rapid shift rotation, they are still exposed to this circadian sleep change's side effects such as general physical fatigue, sensory-neurological fatigue, poor perceived sleep quality, daily dysfunction, difficulty in learning, and memory. They show a significant difference compared to people working on a regular workday.

Keywords: Fast shift work rotation, learning, mental fatigue, shift workers, sleep quality

How to cite this article:
Naeini SA, Habibi E, Shokrolahi I. The effect of sleep quality and mental fatigue on the learning rate of shift workers with fast shift work rotation. Indian J Occup Environ Med 2022;26:225-9

How to cite this URL:
Naeini SA, Habibi E, Shokrolahi I. The effect of sleep quality and mental fatigue on the learning rate of shift workers with fast shift work rotation. Indian J Occup Environ Med [serial online] 2022 [cited 2023 Apr 1];26:225-9. Available from:

  Introduction Top

Although sleep quality parameters are not precisely defined, more than 30 min of delay in falling asleep, waking up 30 min after the sleep onset, sleep efficiency less than 85%, or sleep duration less than six and a half hours are considered clear signs of poor sleep quality. They are also regarded as significant clinical symptoms when accompanied by having difficulty starting or maintaining sleep, waking up early, or chronic non-restorative sleep occurring three or more nights a week. If these symptoms last more than 1 month, it indicates chronic insomnia.[1] Shift workers are at risk of circadian rhythm disorders, known as a type of Shift Work Disorder. General clinical conditions for work shifts include working night shifts, starting work very early in the morning (4 to 7 in the morning), or working on a rotating shift schedule.[2] Shift work is also identified as a hazard in the workplace.[3],[4] Studies have also shown that there is consensus among experts about some index of Education and public health initiatives requires good sleep quality,[5] and other studies have indicated that less than 7 h of sleep is associated with dysfunction.[6]

On the other hand, in today's workplace environments, career tasks rely on cognitive function, that is, mental processes that play an essential role in information processing such as paying attention, decision making, and learning, which also have a significant role in jobs that require acquiring knowledge and continuous learning.[7],[8]

In a study, shift workers' learning was assessed by the Math-Addition Test and the Digit Symbol Substitution Task, and circadian incompatibility was identified as a detrimental factor in learning.[9]

Behaviorally, mental fatigue is defined as a reduction in performance (accuracy and reaction time) in cognitive activities.[10],[11],[12] Studies have also shown that mental fatigue reduces physical function (duration and intensity of physical activity).[13] In the workplace, mental fatigue has been identified to increase the risk of making errors.[14]

This study assessed the quality of sleep and mental fatigue on shift workers' learning rate. It can also help manage the workplace, increase productivity, reduce human errors, and save lives and property.

  Materials and Methods Top

This study is a descriptive-analytical and applied research. The sample size is determined according to individuals' average learning rate in the pre-test. The initial test results, which were performed on 10 people, were used to obtain the sample size. The sample size of 35 people for each group was calculated separately with a 95% confidence interval. More people were examined to be more specific (36 full-time daytime workers and 44 shift workers, who were working night shifts during this study). The entire statistical community was selected from the male gender to eliminate the effect of gender on the results. The shift rotation is fast (2 days), and the working hours are from 6 am to 2 pm, 2 pm to 10 pm, and 10 pm to 6 am, but the morning shift, that is, regular shift (7 am to 4 pm) was selected to check for circadian rhythm changes.

Inclusion criteria were having no visual impairment, no history of cardiovascular disease, no respiratory problems, and no history of cardiovascular, hypoglycemic, depression, sedative drugs, and Parkinson's drugs. Subjects participated in the study voluntarily. Besides, the tests were then fully described to the participants.

In this study, the Pittsburgh Sleep Quality Index (PSQI)[15] and mental fatigue checklist developed by the Japan Industrial Safety and Health Association[16] were used to evaluate the effects of work shift, sleep quality, and mental fatigue on learning behavior and memory pattern. The PM-MZ4871-4 maze device was used to investigate the amount of learning assessed by recording and reporting the number of errors and measuring the time of solving the labyrinth (maze). This labyrinth consists of paths through which the candidates must find the correct path to reach the target with closed eyes by the existing electrode. Finally, the driven data were analyzed using SPSS software version 26.

  Results Top

This research was conducted to evaluate the perception of employees and their sensory-motor movements. The demographic data of these people can be seen in [Table 1].
Table 1: Demographic characteristics of the personnel

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Pittsburgh sleep quality index

The average of the seven scales measured in the Pittsburgh Sleep Quality Index and the desired and undesirable sleep range for each scale can be seen in [Table 2].
Table 2: Average scales measured in the Pittsburgh Sleep Quality Index in each group along with the average and range of desirable and undesirable sleep range in each scale

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Delay in shift workers' falling asleep was almost three times more than ordinary workers, and sleep disturbances in shift workers were more than two tmes compared to daytime workers. Besides, daily dysfunction was reported to be significantly (three times) higher for shift workers.

Analysis of data on personnel's sleep quality showed that 63.6% of shift workers and 16.7% of daytime workers were at an undesirable level, and a total of 42.5% of staff had poor sleep quality.

Although shift workers have longer sleep duration and more sleep efficiency than daytime workers, shift workers experience poor sleep quality and receive a final score of 7.5 in general [Figure 1].
Figure 1: Comparison of scores obtained from the PSQI in the two groups of daytime workers and shift workers

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A modified three-factor model proposed by Cole et al.[17] was also examined. In Cole's three-factor model [Table 3], shift workers have three times more perceived sleep quality than daytime workers, but shift workers' sleep efficiency has been two times more than daytime workers' sleep efficiency. Shift workers also experience more sleep efficiency and daily disturbances [Figure 2].
Table 3: Cole et al.'s three-factor model with the desirable and undesirable range of the three factors

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Figure 2: The revised 3-factor scoring model as proposed by Cole and colleagues

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Measuring mental fatigue

The average scores of mental fatigue at the beginning and end of the shift for A, B, and C parts are shown in [Table 4]. The scores of each section represent the average scores of the 10 items related to that section.
Table 4: Mental fatigue checklist values in three parts of A, B, and C in two groups of daytime workers and shift workers at the beginning and end of the shift

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Part A scores, which indicate general and physical fatigue, increased at the beginning and end of the day and night shifts. Fatigue scores in part B indicate the mental fatigue of individuals (without a physical basis). Mental fatigue is reduced at the end of the day work and is relatively less at night. Fatigue scores in part C indicate sensory and nervous system fatigue. Shift workers reported more fatigue at the end of the shift compared to the beginning of the shift [Figure 3].
Figure 3: Comparison of three parts of A, B, and C in the mental fatigue questionnaire at the beginning and end of each shift

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Measuring the learning rate

The mean and standard deviation were calculated for the learning time parameters and the number of learning errors for daytime workers and shift workers at the beginning and end of the shift [Table 5].
Table 5: The mean and standard deviation of learning at the beginning and end of the shift

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As can be seen, the average learning time at the end of the day work and shift work has increased; this increase in learning time in the night shift is significant compared to the day work. The average number of errors at the beginning and end of the morning shift does not show much change. However, the number of errors at the end of the night shift were 1.67 times more than at the beginning of this shift. On the other hand, the number of errors in the day shift has been declining. In other words, regardless of the learning time, the person has made fewer mistakes at the end of the shift even though they were trivial.

The significance and relationship of learning at the beginning and end of the shift are described in [Table 6].
Table 6: P value for learning time and number of learning errors

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As shown in [Table 6], a significant relationship was observed between learning time and the number of learning errors at the beginning and end of the morning shift and night shift. However, [Table 7] did not show a significant relationship between sleep quality and learning time and the number of learning errors in the morning and work shifts.
Table 7: Investigating the relationship between sleep quality and learning time and error changes

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  Results and Discussion Top

Considering the modified model of Cole et al., daily disturbances are significantly higher for shift workers. It is probably due to more sleep disorders and more daily dysfunction [Table 3]. Sleep dysfunction can lead to severe daytime dysfunction.[18] The total sleep score in shift workers is 7.5 (higher than 5), which indicates that shift workers experience undesirable sleep.

As shown in [Figure 3], the difference between part A's fatigue at the beginning and end of the night shift was two times this difference at the beginning and end of the morning shift. It means that people in shift work with the same working hours as daytime workers experience two times as much general fatigue as those working in the morning.

In part B, it is observed that this mental fatigue is almost the same as at the beginning of the shift in night shifts [Table 4]. In part C, fatigue scores indicate that shift workers experience more sensory and nervous system fatigue at the end of each shift. Research has shown that methods that require eye-hand coordination are disrupted after 24 and 34 h of being on call.[19]

In the rapid shift rotation, people do not have enough time to adapt to changes in circadian rhythms, but it can be seen that these changes in work shifts (even rapid ones) have a significant effect on neurosensory disorders in shift workers. However, studies have shown that in fast-rotating systems, the circadian rhythm retains its daily characteristics and avoids the accumulation of sleep deprivation that occurs during long shifts.[20]

As mentioned before, according to the P values mentioned in [Table 6], the learning time at the beginning and end of the night shift had a significant relationship, and the error rate and learning time at the end of this shift increased, so there was a reverse relationship between them. It seems that impaired brain activity due to cortisol levels disorder, cumulative sleep deprivation, or insufficient sleep is possible. According to [Table 7], since no significant relationship between learning and sleep quality has been reported, poor sleep quality may have a greater impact on memory than learning. However, it can be said that learning and memory work better at the beginning of the morning shift [Table 6].

Seemingly, shift workers cannot manage heavy workloads or high-responsibility tasks due to circadian changes (even with rapid rotation), poor sleep, and excessive fatigue at the beginning and end of the shift. Besides, they may have poor performance in decision-making, memory recovery, and critical situations and make more mistakes, which may be due to mental or sensory neurological errors. These people start the shift with much fatigue and end it with extreme exhaustion. Consequently, shift workers seem to need more leaves than daytime workers. Furthermore, unadapted night workers are likely to make it difficult to maintain consciousness.[21]

As depicted in [Table 4], fatigue changes in the night shift are less than in the morning shift, indicating better stability of mental performance in shift workers. As previous studies have revealed, mental work is done relatively well during the night shift.[22] This study suggests that this circadian sleep change's side effects, such as general physical fatigue, sensory and neurological fatigue, poor perceived sleep quality, daily disturbances, difficulty in learning, and memory, will influence shift workers continuously (even with fast-rotating work shifts).


This article is the result of the research project of Isfahan University of Medical Sciences. The researchers thank the industry and the people involved in this research. The research project number and ethics code are 198008 and IR.MUI.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]


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