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.     

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.     

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.     

Work satisfaction, health, and stress: A study of Dutch nurses

A study was conducted to compare nurses' work satisfaction and feelings of health and stress in five different nursing departments: a cardiac care unit and a general surgical ward in a general hospital; and an admissions department, a short-stay department, and a long-stay department in a psychiatric hospital. One hundred nurses took part in the study: the instruments used were questionnaires and structured interviews. The main results showed that:

(1) nurses in the cardiac care unit had the most positive satisfaction scores

(2) nurses in the general surgical ward had the most positive scores on the health and stress variables

(3) feelings of dissatisfaction and stress were most prominent in the short-stay department and, to a lesser extent, in the long-stay department.

The findings are interpreted in terms of the different work situations and die implications for hospital management are discussed.

Dr J. A. Landeweerd graduated in industrial and organizational psychology in 1968 (PhD in 1978). He has worked at Eindhoven University of Technology (Department of Industrial Engineering) and now holds a position as senior lecturer at Limburg University (Department of Health Sciences), where he is project-leader for a number of research projects on the relationships between work and health.

Nicolle Boumans, MA, graduated in health sciences in 1985 (specialization: nursing science) and is now a research assistant. She is working on a PhD thesis concerned with the relationship between task characteristics of nurses and their reaction in terms of job satisfaction, health and stress.     

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.     

Book reviews and books received

Managing Stress Edited by David Fontana, Leicester, BPS/London, Routledge (1989). [Pp.ix + 118.] 5.95. ISBN 0-901715-98-0 (hardback). ISBN 0-901715-97-2 (paperback).

Applying Cognitive Psychology to User Interface Design Edited by M. M. GARDINER and B. CHRISTIE, New York, John Wiley (1987). [Pp.ix+372.] A29.95. ISBN 0-471-91184-4.

Architect or Bee? The Human Price of Technology Edited by MIKE COOLEY, London, The Hogarth Press (1987). [Pp. 193.1 E5.95 (paperback). ISBN 0-701207-69-8.

Occupational Health, 2nd Edition Edited by BARRY S. LEVY and DAVID H. WEGMAN, Boston, Little Brown (Edinburgh, Churchill Livingstone) (1988). [Pp. xxv + 640.1 A24.95 (Paperback). ISBN 0-316-52247-3.

Stress Management in Work Settings Edited by LAWRENCE R. MURPHY and THEODORE F. SCHOENBORN, Washington DC, US Government Printing Office (1987). [Pp. viii+ 190.1 $9.50. DHHS (NIOSH) Publication No. 87-111.

Trends in ErgonomicslHuman Factors V Edited by FEHEVDOUN AGHAZADEH, Amsterdam, North-Holland (Elsevier), (1988). [Pp. xx + 1095.1 $208, Dfl. 395. ISBN 0-444-70442-6.

Technology and the Transfarmation of White Collar Work Edited by ROBERT E. KRAUT, New Jersey, Lawerence Erlbaum Associates (1987). [Pp. x + 281 .] A21.50. ISBN 0-89859-633-5.     

Book reviews and book received

Handbook of Occupational Medicine. Edited by Robertj. McCunney, Boston, Little, Brown and Co (1989). [Pp. xxiv+511.] £15.95. ISBN 0-316-55528-2 (paperback).

Lgestyle, Stress and the Mitchell Method of Relaxation [Video]. By Laura Mitchell, Leeds, International Stress and Tension Control Society (1989). £19.50.

Crisis Intervention Verbatim. By Nira Kfir, New York, Hemisphere/London, Taylor & Francis (1989). [Pp. xxv + 169.] £18.00. ISBN 0-89116-837-0 (hardback).

Total Back Care By Cristopher R. Hayne, Health Right Series, London, J. M. Dent & Sons Ltd (1987). [Pp. xiii + 144.] £3.95. ISBN 0 460 02439 6.

Adaptive Physiology to Stressftrl Environments Edited by Shlomo Samueloff and Mohamed K. Yousef,Boca Raton, Florida, CKC Press (1987). [Pp. x+212.] £104.00, US$130.00. ISBN 0 8493 6458 2.

Psychophysiology and the Electronic Workplace Edited by Anthony Gale and Bruce Christie, Chichester, Wiley (1987). [Pp. x +351.] £36.50. ISBN 0 471 91373 7.

Environmental Ergonomics: Sustaining Human Perfrmance in Harsh Environments Edited by Igor B. Mekjavic, Eric W. Banister and James B. Morrison, London, Taylor & Francis (1988). [Pp. xiv+412.] £39.00. ISBN 0-85066-400-4 (hardback).     

The psychosocial work environment of district nurses in Sweden

Data were collected from a stratified sample of district nurses in the greater Stockholm area on four occasions during one year using questionnaire techniques (to assess psychosocial working conditions and social networks, and self-reported health sums); as well as physiological measurement techniques. Three groups of district nurses were compared: group A, those working independently in the 'traditional' role but outside primary health care centres; group B, those working independently in the 'traditional' role but in primary health care centres; and group C, those working in the model role as part of primary health care teams. The study focused on the effects of these different work environments on the district nurse's psychological and somatic health, and their physiological state.

The data suggested that district nurses in the primary care teams (group C) had a lower objective work load than those working in the more traditional role. Despite this, they reported a less favourable balance (ratio) of work demands to decision latitude. They reported more 'problems' and 'conflicts' at work than did the other district nurses. However, such 'problems' were diminishing during the study period, which could mean that successive adaptation to the 'new' situation was occurring. The 'conflicts', on the other hand, remained. This may indicate that despite this adaptation, the district nurses in the primary care teams were struggling with their new work roles. It points to the need for organizational support during this important change process. The district nurses in group B (traditional role but in a primary health care centre) had the highest objective work load and showed physiological reactions in terms of elevated plasma cortisol levels in the morning, high systolic blood pressure and sleep disturbances.     

Stress, health and the working environment of Swedish prison staff

A random stratified sample of just over 2000 was drawn from staff working in 67 different prisons in Sweden. Questionnaires on working conditions and symptoms of ill health were administered and subjects were given health examinations. Morning plasma Cortisol and gamma glutamyltransferase (g GT) levels were measured and factual information on the prisons was collected for use in the analyses.

There were differences between prisons in terms of both objective and self-reported working conditions which appeared to affect health status, physiological state and sick leave rate. Cardiovascular and hypertensive conditions were found more often among prison staff than among a large reference group made up of many different occupations. Sick leave rates among prison staff, especially those over 45 years old, were very high compared with this reference group. The situation appeared particularly difficult in prisons with a high proportion of drug abusing inmates.

The data allowed the identification of several factors which might counteract the effects of stress at work: a proactive management style, goal consensus among staff, a high degree of decision latitude, satisfaction with work performance and a supportive psychosocial climate.     

Auditory evoked potentials as a function of sleep deprivation

Event-related brain potentials (ERPs) were studied in subjects deprived of sleep over a 48-h test period to assess the effects of different durations of continuous wakefulness on ERP components and to determine whether changes in the ERP components were related to changes in performance. Forty subjects were randomly assigned to either an experimental (sleep deprived) group (n = 30) or a control (not sleep deprived) group (n = 10). For the experimental subjects, ERP and performance measures were obtained in four-h test blocks throughout the 48-h period. Performance was assessed using the Walter Reed performance assessment battery. The control subjects were tested at the same times except during designated sleep periods. Both performance and evoked potential measures showed systematic changes over the experimental test period in association with sleep deprivation, time of day, and repeated testing. The latency of the N2 component of the evoked potential covaried with throughput measures on the performance assessment battery across the 12 four-h test blocks of the experiment. These data suggest that ERPs reflect central processes that change across the sleep deprivation period and that ERP measures might be useful in assessment and prediction of performance degradation under adverse conditions such as sleep loss.     

Biochemical assessment and differentiation of mental and physical effort

Evaluation of mental effort under industrial conditions encounters both methodological and practical problems mainly because of lack of appropriate indices and difficulties in differentiation between body responses to physical and mental effort.

This paper presents a review of laboratory and field research from our laboratories aimed at finding objective indices for discrimination between body responses to mental and physical effort. The laboratory data show that urinary noradrenaline/adrenaline (NA/A) ratio decreases in response to mental tasks and increases in response to physical tasks. Under industrial conditions the predominating component of effort (mental or physical) evokes body response similar to that found during laboratory experiments. Re-analysis of data published in various other papers shows the same pattern of body response.

Another possible index for assessment of effort seems to be salivary cortisol which increases in response to both mental and physical tasks. Its deviations from the circadian pattern of excretion may represent a potential criterion for assessment of the emotional component of mental effort.     

Circadian rhythms and bright light: Recommendations for shift work

This paper starts with a brief review of the basic principles of human circadian rhythms relevant to understanding the problem of shift work. It then presents a more detailed critical review of the recent bright light literature, with an emphasis on methodological shortcomings, alternative interpretations, and areas that need further research. Evidence is presented which suggests that either a light-dark cycle (which includes bright light) or a sleep-wake schedule can act as a zeitgeber for human circadian rhythms. Current human phase response curves to bright light are reviewed. Light-work-sleep schedules are presented which have been designed to eliminate the physiologically based harmful consequences of shift work. These schedules include both bright light and sleep-wake schedule zeitgebers. Other practical applications of bright light treatment are mentioned.     

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.     

Sustained work, fatigue, sleep loss and performance: A review of the issues

The physiological and psychological stressors associated with sustained work, fatigue, and sleep loss affect worker performance. This review describes findings relating to sustained work stresses commonly found in our advancing technological world. Researchers report decrements in sustained performance as a function of fatigue, especially during and following one or more nights of complete sleep loss, or longer periods of reduced or fragmented sleep. Sleep loss appears to result in reduced reaction time, decreased vigilance, perceptual and cognitive distortions, and changes in affect. Sleep loss and workload interact with circadian rhythms in producing their effects. These interactions are a major source of stress in work situations requiring sustained work in continuous operations and have implications for theoretical models of sustained perceptual and cognitive functioning.     

Performance, alertness, and sleep after 3·5 years of 12 h shifts: A follow-up study

Control room operators at a continuous processing plant have been working a 12 h/3-4 day rotating shift schedule for over 3 years. After 7 months on this schedule, our initial assessment indicated decrements in performance and alertness, and a mild to moderate sleep debt, when the 12 h shift schedule was compared to the previously-worked 8 h shift schedule. In an effort to track long-term adaptation to the schedule, we conducted a 3 & 5 year follow-up evaluation using the same set of measures. Long-term follow-up testing revealed persistent decrements in performance and alertness attributable to 12 h shifts, and 1-3 h reductions in total sleep time after 12 h night shifts. Little deterioration in performance or alertness was observed across the workweek, which suggested day-to-day recovery from the extended workshift. The popularity of the 12 h shift schedule at this worksite indicates that the workers are willing to tolerate extra fatigue to derive other benefits from this schedule.     

Pilot Study Sleepiness in physicians on night call duty

Little is known about how physicians' feelings of sleepiness and sleep patterns are affected by night call duties. In the present pilot study, the authors followed a group of staff (hospital) physicians during and following night call duties. They recorded feelings of sleepiness and sleep patterns every third hour. Results show measurable effects on the sleepiness scale with residual effects lasting up to two days after the actual night call duty. The authors suggest that increased attention should now be given to studies of the psychophysiological effects of both present and alternative work schedules for physicians.     

The impact of shiftwork on personnel at a nuclear power plant: An exploratory survey study

Shiftwork may constitute an additional risk factor in high-hazard industries where system failure could exact heavy human, environmental and economic costs. This exploratory survey study examined the impact of shiftwork upon nuclear power plant workers' perceived health, sleep, and social problem, as well as levels of alertness. Overall, the night shik proved to be the most problematic in ternis of decreases in alertness, sleep duration and quality, and disruptions to health, social and family life. The permanent shift preferences of the shiftworkers were also explored to establish the practicability of introducing a theoretically safer permanent mght shdt at such a facility. Importantly, the small proportion of the sample who showed a preference for a pemianent night shift was insufficient to provide operational cover. Although these shtftworkers reported experiencing less disruption on the night shift than those who would choose to work a permanent day shift, their preference appeared to be based upon a greater esprit de corps on this shift rather than on any predisposing individual characteristics. These results have practical implications for work scheduling in high-hazard industries.

The present study investigates the dimensional structure of the psychosocial work environment as assessed by Karasek's job characteristics scales and a set of factorial scales derived from the Dictionary of Occupational Titles (DOT) observers' ratings of occupational characteristics for census occupations. Scale scores on the Karasek and DOT were linked to information on occupation from the Epidemiologc Catchment Area (ECA) study sample. Scale intercorreladons and factor analysis were performed on those ECA subjects who reported ever having a full-time job (n=11,789). DOT'sS Substantive Complexity scale was positively correlated with Karasek's Skill Discretion and Decision Authority scales, and DOT's Physical Demands and Hazards scale was positively correlated with Karasek's Physical Demands scale. In addition, the DOT system compared to the Karasek system seems to assess psychosocial work domains less characteristic of traditional industrial jobs (interpersonal stress, expressive work). The content validity of the Karasek scales might be increased with the assessment of these domains. Giving support to Karasek's Demand/Control Model, the factor structure of the psychosocial work enviromnent in the probability sample of five US metropolitan populations yielded two major dimensions: Control, and Physical Demands.     

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.     

Stress factors among lecturers in a college of further education

This article presents some of the findings of a pilot study of sources of stress among lecturers working in a college of further education. The empirical work was carried out over a four-week period, with lecturers, chosen at random, being asked to participate using one or all of the three research methods employed: personal interviews, completing a questionnaire, and keeping a diary.

The study set out to address two broad questions. First, 'What are the experiences that can give rise to stress and, having identified them, how often do these experiences occur?' Second, 'Having identified the sources of stress, did the lecturers feel that such experiences affected their teaching, their preparation for teaching or their assessments as a result of teaching?'

The data highlighted the fact that mere were four broad problem areas or sources of stress within this college of further education and that some were seen to occur 'frequently'. However, whether such sources of stress affected actual teaching was not dear, but mere was some support for the notion that the preparation for teaching and the assessment as a result of teaching were affected.