Post-lunch nap as a worksite intervention to promote alertness on the job

A worksite study was conducted to examine whether a 15-min nap during a post-lunch rest period would affect subsequent alertness, performance, and nocturnal sleep in eight factory workers under a 3-week protocol. Subjects were asked to take the nap at 12:30?h on a reclining chair during the nap week, and to remain awake during the no-nap week. The order of these 2 weeks was counterbalanced between the subjects. During the third, follow-up week, each subject determined whether or not she/he would nap. Alertness on the job and nocturnal sleep were assessed using a sleep diary. Wrist activity was also recorded during sleep at night. Choice reaction time task (RT) was performed at 10:00 and 15:00?h every day of the nap week and every other day of the no-nap and follow-up weeks. Perceived alertness was significantly higher in the afternoon after nap than after no nap at the end of the week. Similar effects were observed during the follow-up week where almost half of the subjects napped. No significant differences between the three weeks were found for RT performance or nocturnal sleep. Workers' attitudes toward the nap were favourable. Although further intervention research is required, our results suggest that post-lunch napping may have the potential to promote daytime alertness at work.     

Post-lunch nap as a worksite intervention to promote alertness on the job.

A worksite study was conducted to examine whether a 15-min nap during a post-lunch rest period would affect subsequent alertness, performance, and nocturnal sleep in eight factory workers under a 3-week protocol. Subjects were asked to take the nap at 12:30 h on a reclining chair during the nap week, and to remain awake during the no-nap week. The order of these 2 weeks was counterbalanced between the subjects. During the third, follow-up week, each subject determined whether or not she/he would nap. Alertness on the job and nocturnal sleep were assessed using a sleep diary. Wrist activity was also recorded during sleep at night. Choice reaction time task (RT) was performed at 10:00 and 15:00 h every day of the nap week and every other day of the no-nap and follow-up weeks. Perceived alertness was significantly higher in the afternoon after nap than after no nap at the end of the week. Similar effects were observed during the follow-up week where almost half of the subjects napped. No significant differences between the three weeks were found for RT performance or nocturnal sleep. Workers' attitudes toward the nap were favourable. Although further intervention research is required, our results suggest that post-lunch napping may have the potential to promote daytime alertness at work.     

Innovative working schedule: introducing one short nap during the night shift.

In order to test the possible long-term effects of the implementation of a short nap during night shifts, an experiment was conducted over a period of 1 year with 12 volunteer shiftworkers operating in an industrial plant. They were authorized, under certain conditions, to use individual sleeping areas, for a maximum of 1 hour, between 23h30 and 3h30. The participants were asked to fill in a short questionnaire every day during the entire study. The questions concerned the schedule of the main sleep period, the afternoon nap and the night-time nap, if any, as well as the evaluation of mood and the quality of work. This daily questionnaire was supplemented by an extensive questionnaire applied every 2 months in order to assess the main changes introduced in the life of the participants by this new working schedule. Results showed that this new organization introduced a general satisfaction about the quality and the easiness of the work at night. The vigilance level was considered to be higher during the hours following the nap. The efficacy of the nap time progressively increased for most subjects. The general quality of life improved for most subjects. While a few of them considered that falling asleep was less easy on the following morning at home, the statistical analysis did not show any detrimental effect of the short rest period on the length of the immediately consecutive main sleep period. However, different statistical analyses allow us to reveal significant differences between the main sleep durations following the night shift compared with those following both the afternoon shift and the resting period. The main sleep duration following the night shift was not statistically different from that of the morning shift. These results are very encouraging. A short nap during the night shift can be considered as a positive way to counteract the low level of vigilance that normally occurs during the late part of the night.     

Innovative working schedule: introducing one short nap during the night shift

In order to test the possible long-term effects of the implementation of a short nap during night shifts, an experiment was conducted over a period of 1 year with 12 volunteer shiftworkers operating in an industrial plant. They were authorized, under certain conditions, to use individual sleeping areas, for a maximum of 1 hour, between 23h30 and 3h30. The participants were asked to fill in a short questionnaire every day during the entire study. The questions concerned the schedule of the main sleep period, the afternoon nap and the night-time nap, if any, as well as the evaluation of mood and the quality of work. This daily questionnaire was supplemented by an extensive questionnaire applied every 2 months in order to assess the main changes introduced in the life of the participants by this new working schedule. Results showed that this new organization introduced a general satisfaction about the quality and the easiness of the work at night. The vigilance level was considered to be higher during the hours following the nap. The efficacy of the nap time progressively increased for most subjects. The general quality of life improved for most subjects. While a few of them considered that falling asleep was less easy on the following morning at home, the statistical analysis did not show any detrimental effect of the short rest period on the length of the immediately consecutive main sleep period. However, different statistical analyses allow us to reveal significant differences between the main sleep durations following the night shift compared with those following both the afternoon shift and the resting period. The main sleep duration following the night shift was not statistically different from that of the morning shift. These results are very encouraging. A short nap during the night shift can be considered as a positive way to counteract the low level of vigilance that normally occurs during the late part of the night.     

The effects of a self-selected nap opportunity on the psychophysiological,performance and subjective measures during a simulated industrial night shift regimen

This study compared the effects of a 1 h self-selected recovery period to those of a standard night shift arrangement (with a total break time of 1-h) over a simulated three-day night shift schedule in a laboratory setting. Results showed that the inclusion of the flexible nap scheme resulted in higher performance output, improvements in physiological strain responses and reduced sleepiness during each night shift and generally over the three-night cycle. Certain variables also revealed the impact of napping compared with the standard rest break condition on the circadian rhythm. The sleep diary records show that the inclusion of the current intervention did not significantly reduce daytime recovery sleep. The results suggest that the potential benefits of flexible napping may outweigh the logistical effort it requires in a workplace environment.

Practitioner summary: Consensus on appropriate napping strategies for shift work remains a challenge. This simulated night shift laboratory study sought to determine the effects of a 1-h self-selected nap opportunity relative to a normal shift set-up. The nap improved performance and decreased sleepiness, without affecting daytime sleep.     

A field study of sleep and fatigue in a regular rotating 12-h shift system

The aim of this study was to examine a regular rotating 12-h shift system (2D2N4Off) at an Australian Smelter. Sleep behavior, subjective fatigue and neurobehavioral performance were investigated over a 14-day period for 20 employees. Activity monitors, sleep/wake diaries, and 5-min psychomotor vigilance tasks were used. Sleep data showed differences between day and night shifts. While sleep prior to night1 was increased relative to day shifts, a reduced sleep length carried into the period leading to night2. Total wakefulness at the end of shift, and subjective fatigue were increased for night shifts, particularly night1. Decrements in performance data supported these findings. Both prior wakefulness and prior sleep are important in a 12-h shift system. Employees may “sleep in” after day shifts, rather than taking extra sleep prior to night work. Thus, sleep between day and night shifts is based on recovery rather than preparation.     

Sleep in a live-in mining operation: The influence of start times and restricted non-work activities

The amount of sleep obtained between shifts is influenced by numerous factors including the length of work and rest periods, the timing of the rest period relative to the endogenous circadian cycle and personal choices about the use of non-work time. The current study utilised a real-world live-in mining environment to examine the amount of sleep obtained when access to normal domestic, family and social activities was restricted. Participants were 29 mining operators (26 male, average age 37.4 ± 6.8 years) who recorded sleep, work and fatigue information and wore an activity monitor for a cycle of seven day shifts and seven night shifts (both 12 h) followed by either seven or fourteen days off. During the two weeks of work participants lived on-site. Total sleep time was significantly less (p < 0.01) while on-site on both day (6.1 ± 1.0 h) and night shifts (5.7 ± 1.5 h) than days off (7.4 ± 1.4 h). Further, night shift sleep was significantly shorter than day-shift sleep (p < 0.01). Assessment of subjective fatigue ratings showed that the sleep associated with both days off and night shifts had a greater recovery value than sleep associated with day shifts (p < 0.01). While on-site, participants obtained only 6 h of sleep indicating that the absence of competing domestic, family and social activities did not convert to more sleep. Factors including shift start times and circadian influences appear to have been more important.     

The role of naps in alleviating sleepiness during an irregular sleep-wake schedule

Abstract

Four groups of four subjects have been studied in an isolation unit on an irregular schedule of sleep and waking. Sleep periods of 6h duration were taken at irregular times during the 9-day protocol; they were arranged such that the waking periods lasted 6, 12 or 18 h and were also in an irregular sequence. One-hour naps were taken after 6 and 12 h of waking if the next sleep was not due then. Just before either a nap or a full sleep, subjects assessed their sleepiness and, on rising, they assessed how well sleep had been initiated and maintained. A mathematical model was developed which enabled the effects upon sleepiness of circadian rhythmicity, of the length of the waking period since the last full sleep (time-since-sleep), and of the subjective value of the previous full sleep or nap to be independently quantified. Results showed that there was a tendency for sleepiness to increase, in some cases quite markedly, as the irregular schedule proceeded. There were also effects upon sleepiness due to circadian changes and the amount of time since the last full sleep. These two effects were similar in size and larger than the benefits to be derived from a previous nap or full sleep that had been assessed at the time as having been a good one. We conclude that one-hour naps can play a small role in decreasing an individual's sleepiness and suggest possible means by which their subjective value might be increased.     

The efficacy of naps as a fatigue countermeasure: a meta-analytic integration

Modern requirements for extended operations in aviation, transportation, the military, and industry have led to extensive research on countermeasures to mitigate the adverse effects of fatigue. The goals of this research were to (a) summarize and integrate existing research on naps as a fatigue countermeasure using meta-analysis, (b) identify the strength and significance of the effects of naps on performance and feelings of fatigue, and (c) identify factors that may moderate the effects of napping as a fatigue countermeasure. The results of these analyses can be used to predict nap efficacy as a function of length of the nap and the postnap interval. The results of these analyses also suggest an approach to work design that takes into account the optimal effects of naps as a fatigue countermeasure. Actual or potential applications of this research include the development of optimal work schedules to minimize fatigue and increase safety.     

Effects of shift schedules on fatigue and physiological functions among firefighters during night duty

To examine the effects of shift schedules on fatigue and physiological functions among firefighters a 17-day field study at a fire station was carried out. Eleven firefighters, who were engaged in firefighting emergency services, participated in this study. At the fire station, night duty (22:00-07:00) was divided into 5 periods (P1: 22:00-00:00; P2: 23:45-01:45; P3: 01:30-03:30; P4: 03:15-05:15; P5: 05:00-07:00). The participants were assigned to one of these 5 periods and awakened to answer calls from the city's central information centre. They took naps in individual rooms during night duty, except when on night shift or when called out on an emergency. Subjective complaints of fatigue, critical flicker fusion frequencies, 3-choice reaction times, and oral temperature were measured before and after work and following breaks during their 24 working hours. Heart rate variability was also recorded to evaluate autonomic nerve activity. The results show that during P3 and P4, participants who had to wake up at midnight took shorter naps. The rates of subjective complaints regarding P3 and P4 tended to be higher than those for P1, P2, and P5. The ratios of the low frequency component of heart rate variability to the high frequency component during P4 were significantly lower than those during P5. It is assumed that such an irregular sleeping pattern causes many complaints of subjective fatigue, and adversely affects physiological functions. A night-duty shift schedule ensuring undisturbed naps should be considered.     

Alertness of night nurses: two shift systems compared

The alertness of hospital trainee nurses during their night shift work was assessed by recording performance at night on an arousal-sensitive unprepared simple reaction time task. One group carried out a number of separate weeks on night shift throughout their three-year course. Here performance fell from first to seventh day of the week on night shift, implying progressive sleep deprivation. Another group covered their night work by a single three-month 'permanent' night shift of four (or three) nights on and three (or four) days off each week. Here initial performance level fell by the 45th night but had returned to normal by the last (90th) night. In both systems individuals varied considerably in their ability to maintain performance during sustained night work. These results strengthen the case for permanent night shifts, with careful selection of personnel, as a means of organizing night nursing in hospitals.     

Sleep and need for recovery in shift workers: do chronotype and age matter?

This study examined associations of chronotype and age with shift-specific assessments of main sleep duration, sleep quality and need for recovery in a cross-sectional study among N = 261 industrial shift workers (96.6% male). Logistic regression analyses were used, adjusted for gender, lifestyle, health, nap behaviour, season of assessment and shift schedule. Shift workers with latest versus earliest chronotype reported a shorter sleep duration (OR 11.68, 95% CI 3.31–41.17) and more awakenings complaints (OR 4.84, 95% CI 4.45–11.92) during morning shift periods. No associations were found between chronotype, sleep and need for recovery during evening and night shift periods. For age, no associations were found with any of the shift-specific outcome measures. The results stress the importance of including the concept of chronotype in shift work research and scheduling beyond the concept of age. Longitudinal research using shift-specific assessments of sleep and need for recovery are needed to confirm these results.

Practitioner Summary: Chronotype seems to better explain individual differences in sleep than age. In view of ageing societies, it might therefore be worthwhile to further examine the application of chronotype for individualised shift work schedules to facilitate healthy and sustainable employment.     

Tolerance of shift work

This study aimed to explore criteria for shift work tolerance and to investigate the relationships between personality traits and states and shift work tolerance. Eighty-nine policemen and police women completed a questionnaire, once during consecutive night shifts and again during rotating shifts, and their responses were used to assess anxiety, emotional control, positive and negative affect, health complaints, sleep quality, difficulties in social and domestic life, and perceptions about shift work. Both the criteria for tolerance and the relationship between tolerance and personality varied according to shift type. Night shift tolerance involved four factors--somatic health, flexibility, sleep and sleep need--while rotating shift tolerance involved three factors--somatic health, flexibility and fatigue. Tolerance of shift work was associated with anxiety, repressive emotional style and mood. During night shifts, anxiety was the most influential personality factor for the somatic health and sleep dimensions of shift tolerance. During rotating shifts, positive and negative moods, rather than trait personality factors, were important predictors of the somatic health and fatigue shift tolerance dimensions. These results suggest a mechanism for more effective matching of workers to suitable shift schedules.     

Re-entrainment of Body Temperature in Experimental Shift-Work Studies

In a series of experimental shift work studies six subjects worked on continuous night shift for three weeks, four subjects worked on a 1-1-1 shift system (1st day morning shift, 2nd day afternoon shift, 3rd day night shift, 4th day off), and two subjects worked on an 2-2-2 shift system (the ‘metropolitan rota’). Rectal temperature was continuously recorded in each experiment.

The greatest changes in the circadian rhythm of body temperature occurred on the second night shift day, and during the first week of continuous night shift working. The changes involved both shifts in the phasing of the rhythm, and alterations in its form. The re-entrainment of the rhythm to its normal phasing took two or more days after two or more successive night shifts, but only one day after a single night shift. Considerable individual differences in the rhythm adjustment to night work were observed.

In a field validation of these findings, 34 shiftworkers in municipal gas and water supply undertakings measured their oral temperature every 2h both on and off duty. Although only very few temperature readings were obtained during sleep periods, the results confirmed, in general, those of the experimental studies.     

Short nap versus short rest: recuperative effects during VDT work

The effects of a 20-min nap during 2 h of visual display terminal (VDT) work were examined. Ten young healthy adults took a 20-min nap or a 20-min rest 1 h after VDT work, followed by another 1 h of VDT work. A 20-min rest temporarily restored subjective sleepiness, but it deteriorated during the additional 1 h of work. In contrast, a 20-min nap maintained subjective alertness and performance level at a higher level and mental fatigue at a lower level for the additional 1 h of work. These results suggest that a short nap would be useful to both fatigue recovery and fatigue prevention during continuous VDT work. The present findings may provide a new work/rest strategy.     

Short nap versus short rest: recuperative effects during VDT work

The effects of a 20-min nap during 2 h of visual display terminal (VDT) work were examined. Ten young healthy adults took a 20-min nap or a 20-min rest I h after VDT work, followed by another 1 h of VDT work. A 20-min rest temporarily restored subjective sleepiness, but it deteriorated during the additional 1 h of work. In contrast, a 20-min nap maintained subjective alertness and performance level at a higher level and mental fatigue at a lower level for the additional 1 h of work. These results suggest that a short nap would be useful to both fatigue recovery and fatigue prevention during continuous VDT work. The present findings may provide a new work/rest strategy.     

Sleep in a live-in mining operation: The influence of start times and restricted non-work activities

The amount of sleep obtained between shifts is influenced by numerous factors including the length of work and rest periods, the timing of the rest period relative to the endogenous circadian cycle and personal choices about the use of non-work time. The current study utilised a real-world live-in mining environment to examine the amount of sleep obtained when access to normal domestic, family and social activities was restricted. Participants were 29 mining operators (26 male, average age 37.4 ± 6.8 years) who recorded sleep, work and fatigue information and wore an activity monitor for a cycle of seven day shifts and seven night shifts (both 12 h) followed by either seven or fourteen days off. During the two weeks of work participants lived on-site. Total sleep time was significantly less (p < 0.01) while on-site on both day (6.1 ± 1.0 h) and night shifts (5.7 ± 1.5 h) than days off (7.4 ± 1.4 h). Further, night shift sleep was significantly shorter than day-shift sleep (p < 0.01). Assessment of subjective fatigue ratings showed that the sleep associated with both days off and night shifts had a greater recovery value than sleep associated with day shifts (p < 0.01). While on-site, participants obtained only 6 h of sleep indicating that the absence of competing domestic, family and social activities did not convert to more sleep. Factors including shift start times and circadian influences appear to have been more important.     

Circadian rhythms in deep body temperature,urinary excretion and alertness in nurses on night work

Fourteen volunteer nurses who worked on the night shift at a local hospital recorded their times of sleep, mealtimes and any illness or complaints for 12 consecutive days which included at least one spell of night work and rest days. Whilst awake they made regular assessments of their alertness and collected frequent urine samples for analysis of the rate of excretion of a number of constituents. Rectal temperatures were automatically recorded throughout the day and night. Volunteers were divided into those who worked 1–3 successive nights (short term) and those who worked longer ‘blocks’ (long term). There was no difference between the two groups when their subjective assessment of alertness during night work was considered and in both groups there was a similar change in circadian rhythms when rest days and work days were compared. However, there were differences in the amount of day-time sleep that was taken, the temperatures measured, both on and off duty, between 20.00 and 08.00 hours and the number of complaints recorded. These differences are discussed in terms of the ‘commitment’ of individuals to night work and of the possibility that this will change with family and social factors.     

Differences in day and night shift clinical performance in anesthesiology

OBJECTIVE: This study examined whether anesthesia residents (physicians in training) performed clinical duties in the operating room differently during the day versus at night. BACKGROUND: Fatigue from sleep deprivation and working through the night is common for physicians, particularly during residency training. METHODS: Using a repeated-measures design, we studied 13 pairs of day-night matched anesthesia cases. Dependent measures included task times, workload ratings, response to an alarm light latency task, and mood. RESULTS: Residents spent significantly less time on manual tasks and more time on monitoring tasks during the maintenance phase at night than during the day. Residents reported more negative mood at night than during the day, both pre- and postoperation. However, time of day had no effect on the mood change between pre- and postoperation. Workload ratings and the response time to an alarm light latency task were not significantly different between night and day cases. CONCLUSIONS: Because night shift residents had been awake and working for more than 16 hr, the observed differences in task performance and mood may be attributed to fatigue. The changes in task distribution during night shift work may represent compensatory strategies to maintain patient care quality while keeping perceived workload at a manageable level. APPLICATIONS: Fatigue effects during night shifts should be considered when designing work-rest schedules for clinicians. This matched-case control scheme can also be applied to study other phenomena associated with patient safety in the actual clinical environment.     

Influence of shift work in process industry on workers' occupational health,productivity, and family and social life: An ergonomic approach

Shift work is a major feature of modern work practices. It involves working at times considered unconventional for most workers, such as at night. Although the community often benefits from such work practices, shift work can be hazardous for both the workers and the community. There are increased risks for accidents and errors, increased sleepiness and fatigue due to difficulties sleeping, increased health problems, and disruptions to family and social life. More shift workers complained of sleep disturbance, poor sleep quality, tiredness at awakening, and sleepiness in work than did non‐shift workers. More shift workers also complained of gastrointestinal disturbances than did non‐shift workers. The aim of this article is to provide general information on shift work, work schedules, and the effects of work schedules on sleep, fatigue, performance, the health of the human operator, and productivity. © 2010 Wiley Periodicals, Inc.