Polyphasic sleep strategies improve prolonged sustained performance: A field study on 99 sailors

In situations where continuous prolonged work demands exist, the habitual nocturnal monophasic (6-8h duration) sleep pattern can rarely be accomplished, and performance effectiveness may sometimes be severely compromised by accumulation of sleep debt. Several studies have shown that naps can be disproportionately effective in recovering functioning during continuous work (CW).

In this study, sleep-wake patterns and their relationship to performance were studied for 99 sailors involved in solo and double-handed ocean sailing races (a model of a highly demanding CW situation). Most sailors spontaneously adopted multiple nap sleep-wake schedules and adapted without major difficulties to such polyphasic patterns. 66.5% had mean sleep episode durations (SEDs) ranging from 20 min to 2h. Overall mean Total Sleep Time (TST) per 24h was reduced from a baseline of 7.5 to 6.3h. Race performance correlated negatively and significantly with mean SEDs and TSTs. Best performance results were obtained by those sleeping for periods of between 20 min and 1 h and for a total of 4.5 to 5.5h of sleep per day.

The results are discussed together with several chronobiological, phylogenetic and experimental studies and issues, all of which suggest that adult humans may have a damped polyphasic sleep-wake tendency. It is also proposed that polyphasic sleep schedules could become promising and feasible solutions for the management of sleep requirements under prolonged CW situations.     

Reciprocal relationships between psychosocial work characteristics and sleep problems: A two-wave study

Sleep problems are common and impair the health and productivity of employees. Work characteristics constitute one possible cause of sleep problems, and sleeping poorly might influence wellbeing and performance at work. This study examines the reciprocal associations between sleep problems and psychosocial work characteristics. The participants were 1744 full-time employed individuals (56% women; mean age 38 years in 2007) from the Young Finns study who responded to questionnaires on work characteristics (conceptualised by the demand–control model and effort–reward imbalance model) and sleep problems (Jenkins Sleep Scale) in 2007 and 2012. Cross-lagged structural equation models are used to examine the associations. The results show that low control and low rewards at baseline predicted sleep problems. Baseline sleep problems predicted higher effort, higher effort–reward imbalance, and lower reward. Sleep problems also predicted lower odds for belonging to the low (rather than high) job strain group and active jobs group. The association between work characteristics and sleep problems appears to be reciprocal, with a stressful work environment increasing sleep problems, and sleep problems influencing future work characteristics. The results emphasise the importance of interventions aimed at both enhancing sleep quality and reducing psychosocial risks at work.     

The benefits of a nap during prolonged work and wakefulness

Abstract

Prolonged work scenarios with demands for sustained performance are increasingly common. Because sleep loss inevitably compromises functioning in such situations, napping has been proposed as a countermeasure. The optimal timing of the nap relative to its benefits for performance and mood is not known, however. To address this issue, 41 healthy adults were permitted a two-hour nap at one of five times during a 56-hour period of intermittent work, with no other sleep. Naps were placed 12 hours apart, near the circadian peak (P) or trough (T), and were preceded by 6(P), 18(T), 30(P), 42(T), or 54(P) hours of wakefulness. Work test bouts occurred every few hours and consisted of a variety of psychomotor and cognitive tasks as well as mood scales completed at the beginning, middle and end of each bout. A total of eight performance and 24 mood parameters were derived from the bouts and compared between groups at all test points prior to and following the naps. An estimate of the extent to which each nap condition differed from the control (P54) condition was derived by totalling the proportion of test points that yielded statistically significant results relative to the total number of tests conducted both before and after naps.

Although all performance and most mood parameters displayed a circadian-modulated deterioration as the protocol progressed, a nap appeared to attentuate the extent of this change in all performance parameters but not in mood parameters. Overall, the timing of the nap across days and within the circadian cycle was irrelevant to its effect on performance, suggesting that it diminished the intrusion of sleepiness into behavioural functioning, even though subjects were phenomenally unaware of this benefit.     

The benefits of a nap during prolonged work and wakefulness

Prolonged work scenarios with demands for sustained performance are increasingly common. Because sleep loss inevitably compromises functioning in such situations, napping has been proposed as a countermeasure. The optimal timing of the nap relative to its benefits for performance and mood is not known, however. To address this issue, 41 healthy adults were permitted a two-hour nap at one of five times during a 56-hour period of intermittent work, with no other sleep. Naps were placed 12 hours apart, near the circadian peak (P) or trough (T), and were preceded by 6(P), 18(T), 30(P), 42(T), or 54(P) hours of wakefulness. Work test bouts occurred every few hours and consisted of a variety of psychomotor and cognitive tasks as well as mood scales completed at the beginning, middle and end of each bout. A total of eight performance and 24 mood parameters were derived from the bouts and compared between groups at all test points prior to and following the naps. An estimate of the extent to which each nap condition differed from the control (P54) condition was derived by totalling the proportion of test points that yielded statistically significant results relative to the total number of tests conducted both before and after naps.

Although all performance and most mood parameters displayed a circadian-modulated deterioration as the protocol progressed, a nap appeared to attentuate the extent of this change in all performance parameters but not in mood parameters. Overall, the timing of the nap across days and within the circadian cycle was irrelevant to its effect on performance, suggesting that it diminished the intrusion of sleepiness into behavioural functioning, even though subjects were phenomenally unaware of this benefit.     

Shiftwork effects in nuclear power workers: A field study using portable computers

This field study of nuclear power shiftworkers reports the use of hand-held computers to record alertness levels, cognitive task performance and workload ratings. Subjective ratings and performance tasks (Search and Memory-5 (SAM-5); Choice Reaction Time (CRT) were completed on the computers at 2-h intervals during selected shifts in the work schedule by maintenance crews and reactor operators. Sleep duration and quality data were also obtained during the 35-day shift cycle. Workload remained relatively stable across shifts. The night-shift was associated with shorter sleep durations and poorer sleep quality. Significantly lower levels of alertness and poorer perforniance for components of the performance tasks were also observed on the night-shift. Tinic-on-shift effects on alertness were evident, where by for the night-shift, especially, alertness dropped dramatically during the early hours. Components of SAM-5 performance showed differential time-on-shift patterning relative to each shift whereas CRT was unresponsive to time-on-shift effects. Significant variations were observed in alertness and performance components during the 12-h night-shift. Perhaps paradoxically, performance on the 12-h night-shift appeared to improve rather than deteriorate during the early-hour period that was associated with the greatest drop in alertness. This was suggestive of extra effort expenditure during this critical period.     

Shiftwork effects in nuclear power workers: A field study using portable computers

Abstract

This field study of nuclear power shiftworkers reports the use of hand-held computers to record alertness levels, cognitive task performance and workload ratings. Subjective ratings and performance tasks (Search and Memory-5 (SAM-5); Choice Reaction Time (CRT) were completed on the computers at 2-h intervals during selected shifts in the work schedule by maintenance crews and reactor operators. Sleep duration and quality data were also obtained during the 35-day shift cycle. Workload remained relatively stable across shifts. The night-shift was associated with shorter sleep durations and poorer sleep quality. Significantly lower levels of alertness and poorer perforniance for components of the performance tasks were also observed on the night-shift. Tinic-on-shift effects on alertness were evident, where by for the night-shift, especially, alertness dropped dramatically during the early hours. Components of SAM-5 performance showed differential time-on-shift patterning relative to each shift whereas CRT was unresponsive to time-on-shift effects. Significant variations were observed in alertness and performance components during the 12-h night-shift. Perhaps paradoxically, performance on the 12-h night-shift appeared to improve rather than deteriorate during the early-hour period that was associated with the greatest drop in alertness. This was suggestive of extra effort expenditure during this critical period.     

Effects of continuous military operations on physical fitness capacity and physical performance

The purposes of this study were to determine the effects of a continuous field artillery scenario on physical fitness capacity and performance and to estimate the physical intensity of the scenario by continuous heart rate monitoring. Twenty-four artillerymen comprising three, 8-man guncrews participated in an 8-day, combat-simulated operation. Body composition and measures of fitness (isokinetic strength of the arms and legs, isometric handgrip strength, dynamic lifting, and upper body anaerobic power) were determined before and immediately following the scenario. Physical performance was assessed by daily ratings from senior noncommissioned officers experienced in artillery operations. The intensity of physical activity and amount of sleep were estimated from continuously recorded heart rate using electrocardiographic tape recorders worn by the soldiers. No changes occurred in body weight or upper body anaerobic power from pre- to post-scenario. However, measures of muscular strength and lifting capacity increased by 12%-18% post-scenario. Physical performance scores were significantly higher on Days 1 and 8 compared to the other days but no differences were seen from days 2 through 7. The mean ±SD for daily sleep was 5.3 ± 1.3 h. The soldiers averaged 22 min and 2.9 min per day, respectively, at heart rates equal to or greater than 50% and 75% of their maximal heart rates. The results suggest that soldiers who are allowed 5 h sleep per day and who are required to perform at relatively moderate levels of physical intensity show no decrements in physical fitness capacity or evidence of physical fatigue for up to 8 days of continuous operations.     

Combined work stresses: Effect of reduced air renewal on psychological performance during 72h sustained operations

Human tolerance limits for sustained operations under the combined stress of stale air and sleep loss were studied in two groups often male volunteers over a 72 h period, with only 1h of sleep permitted after 32, 48 and 60h. The experiment investigated whether such sustained performance might be additionally influenced by mild hypoxia (15 vol% O₂) together with correspondingly increased carbon dioxide levels (5 vol%).

Performance on various psychological tests showed the expected decrease with increasing duration of sleep loss. However, there were no clear cut differences in performance between the control and the hypoxia groups. There were, however, more pronounced decreases with time in either group in the more complex tasks as compared to simple reaction time and vigilance tasks. Short-term memory improved probably due to learning. The missing effect of hypoxia could be attributed to a hyperventilation response in the experimental subjects and an increase in cerebral blood flow initiated by the hypercapnia.     

Is there an optimum number of night shifts? Relationship between sleep, health and well-being

By concentrating on the impact of a specific shift-system feature on the well-being of those concerned, rather than on the impact of the shift system as a whole, one might be able to offer more meaningful suggestions as to what constitutes a better form of shift system. The present study focused on the impact of the number of consecutive night shifts worked on the health and well-being of two groups of nurses (permanent night and rotating shift). All nurses completed a copy of the Standard Shiftwork Index, which is a set of questionnaires designed for comparing the effects of different types of shift system on large groups of workers. It includes measurements of psychological ill-health, physical ill-health, chronic fatigue, social and domestic disruption, attitudes towards shiftwork, sleep quality and sleep habits. Results showed clearly the impact of the number of consecutive nights worked on health and well-being, not directly, but indirectly through the impact on sleep duration and sleep quality. Sleep duration was shown to increase with more consecutive nights worked. This in turn was found to predict sleep quality, which in turn was found to be the stronger direct predictor of psychological and physical ill-health: i.e. better health was associated with longer and better quality sleeps. Explanations in terms of circadian adaptation are discussed.     

Dealing with shift work: Physical fitness, temperature, and napping

This paper reviews the effects of generally controllable factors such as physical conditioning, ambient temperature, and amount of prior sleep in adjustment to night work periods and shift work. One can expect a 5-10% decline in capacity for work in nocturnal work periods as compared to daytime work periods. This decreased capacity would dissipate if workers maintained a consistent sleep-wake routine for 8-16 days after moving to a new shift. Proven means for accelerating this adaptation are currently not available. The ability to perform work also declines as the length of the work period increases but depending upon individual tasks. Physical conditioning improves mood and general well-being, but no strong evidence currently indicates that conditioning increases tolerance or adjustment to shift work.

Increased ambient temperature increases the stress of work, although studies do not address heat as a factor in adjustment to shift work. While lower nocturnal temperature would be assumed to reduce heat stress during night shifts, supporting data does not exist. Studies have not addressed the negative consequences of cold stress or of rotating from night to day shifts with added heat stress.

The proper use of short sleep periods either as preparation for or as a response to a shift change can ameliorate some effects of shift rotation. Data indicate that performance on 'graveyard' shifts can be maintained close to baseline levels following true prophylactic naps while performance may decline by up to 30% when such naps are not taken. While there is evidence that naps or even rest periods without sleep are beneficial in improving mood in normal young adults, these data do not apply to 'replacement' naps. Studies of interjected naps imply that such naps do reduce sleep debt but do not imply that such naps are more beneficial than longer sleep periods. Naps appear to be most advantageous when the accumulated sleep debt is least.     

Is there an optimum number of night shifts? Relationship between sleep,health and well-being

Abstract

By concentrating on the impact of a specific shift-system feature on the well-being of those concerned, rather than on the impact of the shift system as a whole, one might be able to offer more meaningful suggestions as to what constitutes a better form of shift system. The present study focused on the impact of the number of consecutive night shifts worked on the health and well-being of two groups of nurses (permanent night and rotating shift). All nurses completed a copy of the Standard Shiftwork Index, which is a set of questionnaires designed for comparing the effects of different types of shift system on large groups of workers. It includes measurements of psychological ill-health, physical ill-health, chronic fatigue, social and domestic disruption, attitudes towards shiftwork, sleep quality and sleep habits. Results showed clearly the impact of the number of consecutive nights worked on health and well-being, not directly, but indirectly through the impact on sleep duration and sleep quality. Sleep duration was shown to increase with more consecutive nights worked. This in turn was found to predict sleep quality, which in turn was found to be the stronger direct predictor of psychological and physical ill-health: i.e. better health was associated with longer and better quality sleeps. Explanations in terms of circadian adaptation are discussed.     

Work performance and health of junior hospital doctors a review of the literature

Concern has been expressed for a number of years about the long working hours and consequent sleep loss often experienced by junior hospital doctors. In recent months there has been renewed pressure for the demanding work schedules, common in many hospitals, to be changed. Concern centres on two related areas, namely the potential effects on the doctors work performance and the effects on their health. This paper reviews the literature relating to both areas and assesses how far the expressed need for change is supported by existing evidence. In addition attention is drawn to aspects of sleep loss and work performance requiring further investigation.     

Perceived physical work capacity, stress, sleep disturbance and occupational accidents among firefighters working during a strike

Fire-fighting and rescue work are arranged in such a way that various kinds of accidents and catastrophes can be handled. In an understaffed situation, such as a strike, this goal may not be met. The objective of this study was to investigate factors associated with perceived physical work capacity, stress, sleep disturbance, and occupational accidents among firefighters who remained at work during an extended strike. A cross-sectional questionnaire study was carried out among 543 firefighters (83% of the target group) in 71 fire brigades in Finland. After the strike had lasted for 9 to 11 weeks, most of the firefighters perceived their physical work capacity to be rather good or very good. Stress increased along with a decreasing number of personnel in a crew (OR= 2.3, CI= 1.0-5.3, for less than 75% of a normal crew vs. normal crew) and with decreasing number of personnel in a shift (OR= 2.4, CI= 1.1-5.4, for less than 25% of normal shift vs. normal shift). Sleep disturbance was reported to occur as soon as the total working time exceeded 50 h/week. Working more than 70 h/week increased the risk of occupational accidents almost 4-fold compared with working no more than 50 h/week. These results suggest that exceptional situations, such as a strike, are a challenge to human capacity. With time, increased stress and sleep disturbance may lead to serious consequences.     

Health, well-being and burnout of ICU nurses on 12- and 8-h shifts

It is generally agreed that some features of shift systems can influence the extent of well-being and health problems experienced by the workers involved. Extended working days (9-12 h) have been found to aggravate some problems associated with shiftwork, especially when the work is mentally and emotionally demanding. The aim of the study was to compare measures of health, sleep, psychological and social well-being, job satisfaction and burnout of ICU nurses on 12- and 8-h shifts. The groups of subjects were matced for age, length of shiftwork experience, marital status and number of hours worked. the 12-h shift nurses, when compared to their 8-h shift colleagues, experienced more chronic fatigue, cognitive anxiety, sleep disturbance and emotional exhaustion. Job satisfaction seems to be independent of the shift duration. The nurses on 12-h shifts reported less social and domestic disruption than those on 8-h shifts. The 12-h shift nurses showed worse indices of health, well-being and burnout tan the 8-h shift nurses. It is suggested that this may be associated with their longer daily exposure to the stress of work. The increased number of rest days of 12-h shift nurses seems tobe insufficient to dissipate the adverse health and well-being effects that built up over their longer shifts.     

Effort-reward imbalance,overcommitment and sleep in a working population

The relationship between workplace characteristics and nocturnal sleep in a working population was investigated. Data from 709 employees (mean age=39 years; 87% men) from two German companies were analysed at the entry of the longitudinal cohort study (overall accrual 73%). We investigated the association between the effort-reward imbalance model at work (Siegrist, ) and self-reported sleep quality and sleep disturbances, as assessed by the Jenkins Sleep Quality Index. Effort and overcommitment were found to be higher, and reward was lower in participants with lower (N=328) vs. higher sleep quality (N=381), as well as in participants with (N=217) vs. without (N=492) disturbed sleep (all ps<.001). In regression analyses, lower sleep quality (R ²=.33) and sleep disturbances (R ² _Nagelkerke=.33) were predicted by older age, female gender (only significant for sleep disturbances), shift-work, lower physical and mental health functioning, and higher overcommitment. Individuals were 1.7 times more likely to report disturbed sleep per standard deviation increase in overcommitment. Gender-stratified analyses revealed that higher overcommitment was associated with unfavourable sleep in men, while in women poor sleep was related to lower reward. The findings suggest that overcommitment at work interferes with restful sleep in men, while in women disturbed sleep may be associated with the amount of overcommitment and perceived job reward and sleep quality associated with the perceived reward.     

Perceived physical work capacity,stress, sleep disturbance and occupational accidents among firefighters working during a strike

Fire-fighting and rescue work are arranged in such a way that various kinds of accidents and catastrophes can be handled. In an understaffed situation, such as a strike, this goal may not be met. The objective of this study was to investigate factors associated with perceived physical work capacity, stress, sleep disturbance, and occupational accidents among firefighters who remained at work during an extended strike. A cross-sectional questionnaire study was carried out among 543 firefighters (83% of the target group) in 71 fire brigades in Finland. After the strike had lasted for 9 to 11 weeks, most of the firefighters perceived their physical work capacity to be rather good or very good. Stress increased along with a decreasing number of personnel in a crew (OR= 2.3, CI= 1.0-5.3, for less than 75% of a normal crew vs. normal crew) and with decreasing number of personnel in a shift (OR= 2.4, CI= 1.1-5.4, for less than 25% of normal shift vs. normal shift). Sleep disturbance was reported to occur as soon as the total working time exceeded 50 h/week. Working more than 70 h/week increased the risk of occupational accidents almost 4-fold compared with working no more than 50 h/week. These results suggest that exceptional situations, such as a strike, are a challenge to human capacity. With time, increased stress and sleep disturbance may lead to serious consequences.     

Is there an optimum number of night shifts? Relationship between sleep, health and well-being

By concentrating on the impact of a specific shift-system feature on the well-being of those concerned, rather than on the impact of the shift system as a whole, one might be able to offer more meaningful suggestions as to what constitutes a better form of shift system. The present study focused on the impact of the number of consecutive night shifts worked on the health and well-being of two groups of nurses (permanent night and rotating shift). All nurses completed a copy of the Standard Shiftwork Index, which is a set of questionnaires designed for comparing the effects of different types of shift system on large groups of workers. It includes measurements of psychological ill-health, physical ill-health, chronic fatigue, social and domestic disruption, attitudes towards shiftwork, sleep quality and sleep habits. Results showed clearly the impact of the number of consecutive nights worked on health and well-being, not directly, but indirectly through the impact on sleep duration and sleep quality. Sleep duration was shown to increase with more consecutive nights worked. This in turn was found to predict sleep quality, which in turn was found to be the stronger direct predictor of psychological and physical ill-health i.e. better health was associated with longer and better quality sleeps. Explanations in terms of circadian adaptation are discussed.     

Work stress and attentional difficulties: An initial study on burnout and cognitive failures

Professional burnout is a stress-related disorder, having mental exhaustion due to work stress as its most important characteristic. Burned out individuals also often complain about attentional problems. However, it is currently not clear whether such complaints are based on true cognitive deficits or whether they merely reflect the way burned out individuals rate their own cognitive performance. To confirm the cognitive complaints we used a cognitive failure questionnaire (CFQ) to assess the level of self-reported attentional difficulties in daily life. We also measured performance on tasks of sustained attention and response inhibition (the SART and the Bourdon-Wiersma Test). We compared three groups: (1) a group of 'burned out' individuals (n=13) who stopped working due to their symptoms and sought professional treatment; (2) teachers at a vocational training institute (n=16) who reported high levels of burnout symptoms but continued to work; and (3) teachers from the same institute (n=14) who reported no burnout symptoms. The level of burnout symptoms was found to be significantly related to the number of cognitive failures in daily life, and to inhibition errors and performance variability in the attentional tasks. To our knowledge, explicit tests of objective cognitive deficits in burned out individuals have not been conducted before. Consequently, this is the first study to indicate that burnout is associated with difficulties in voluntary control over attention and that the level of such difficulties varies with the severity of burnout symptoms.     

Leaders' and subordinates' attachment orientations,emotion regulation capabilities and affect at work: A multilevel analysis

Two studies examined relationships between leaders' and subordinates' attachment orientations, emotion regulation capabilities, and affective experience and satisfaction at work. As expected, supervisors' and subordinates' insecure attachment orientations (higher anxiety and avoidance) were associated with own positive affect and satisfaction at work. Supervisors' anxious attachment orientation was associated with subordinates' lower positive affect and satisfaction at work. Contrary to hypotheses, supervisors' higher avoidance was associated with subordinates' lower negative affect and higher job satisfaction. Supervisors' emotion regulation capabilities did not mediate relationships between supervisors' insecure attachment orientations and supervisors' own or subordinates' affect and job satisfaction as expected. However, subordinates' emotion regulation capabilities interacted with supervisors' attachment orientations to predict subordinates' emotion experience at work. The results contribute to an understanding of attachment orientations' emotion dynamics in leader–follower interaction, pointing in particular to perceptual and affect-related processes at different levels of analysis.     

Behavioural techniques for enhancing alertness and performance in shift work

This paper reviews behavioural and cognitive methods for increasing alertness, enhancing performance, and decreasing long-term negative consequences due to shift work. Methods having the most potential for effective intervention include the short-term alerting effects of the optimal timing of work breaks, social activity during breaks, and sensory stimulation. Stress coping techniques and sleep hygiene information for workers and their families have the most potential for addressing long-tcrm effects of shift work. Recommendations for areas requiring further investigation include the altering effects of bright light, fresh air, and cold water; performance enhanccmcnt through psychophysiological self-regulation and imagery; and the impact on performance of second jobs and family responsibilities.