The introductory chapter of this book provides a basic understanding of the factors which determine night work (social, technical, and economic), as well as an assessment of the economic and social costs and benefits of night work.

Various aspects of differing work hours are addressed in this book. Articles written by a number of authors are included and cover the following topics: the reduction of work hours; the influence of collective bargaining; the influence of legislation; hours of work in Canada; hours of work and moonlighting; the economics of overtime; shiftwork and the shorter workweek; and, automation, rationalization, and urbanization.

This book provides a comprehensive introduction to shiftwork. The extent of shiftwork, reasons for adopting and extending shiftwork, choices in systems or schedules, effects on the worker's performance and health, effects on family and social life, worker's attitudes, and institutional factors are discussed.

Although it is difficult to estimate the extent of shiftwork in industrialized countries, it is believed that between 13.4 and 37 percent of all employees are involved in shiftwork. The extent of shiftwork is increasing overall, although it varies between industry, size and type of organization, and country. Generally, it has been found that the proportion of shiftwork increases with the size of the organization.

Reasons for the adoption of shiftwork are complex, involving technical and economic considerations. Differing requirements for the adoption of shiftwork imply differing methods of organizing and arranging shiftwork schedules.

The purpose of this research was to provide background information on the prevalence of shiftwork as well as some of the determinants that underlie shiftwork. Specifically, this research as designed to: 1) provide estimates of the prevalence of shiftwork among single- and dual-earner couples in the U.S.; and 2) focus on the determinants of shiftwork among full-time dual-earners, especially with regard to the job and family characteristics of both spouses. Data obtained from the May 1980 Current Population Survey was used for this study.

With regard to dual-earners, over one-fourth of the couples were found to include at least one spouse who works shifts when both spouses are employed full-time. For these couples, husbands were twice as likely as wives to work shifts. When one or both spouses are employed part-time, the prevalence of shiftwork among dual-earners is even higher; two-thirds of these couples fell into this category. Single-earner couples were found to have a lower prevalence of shiftwork when compared to dual-earner couples.

This article gives a brief description of circadian rhythms and the consequences of changes in these rhythms. These consequences include: more serious accidents on the night shift (although fewer in number), lower productivity, poorer general health, increased absenteeism, and less sleep.

Some preventive measures for shiftworkers are offered and include: selecting workers who indicate the ability to adapt to shift schedules; training to adjust to sleep schedules and sleeping conditions; a rational scheduling plan for shifts; and adaptive meal plans.

This article provides an overview of the circadian timing system and the effects of desynchronosis resulting from transmeridian travel and shiftwork. Additionally, the authors provide a summary of the individual factors which can effect the rate of adjustment to shift schedules. They report that people who adjust more rapidly to rotating work schedules are characterized by "rhythm amplitude and stability and by their waking time preference." Specifically, people with low-amplitude body temperature rhythms can adjust more rapidly to changes in their sleep/wake and activity/rest schedules. People with inert or rigid circadian rhythms have more difficulty during work schedule changes, as compared with people with "labile" or flexible rhythm patterns. Notably, this article states that labile circadian systems and smaller amplitudes in temperature rhythm are characteristic of evening people or "owls."

Sunlight is a strong zeitgeber for the human circadian system. The research reported in this study suggests that artificial illumination can be designed to alleviate the chronobiological disorganization resulting from shiftwork or jet-lag. Specifically, this study examines the effects of bright light (2000 lux) exposure from 5:00 a.m. to 7:00 a.m. on temperature, plasma cortisol, alertness and performance level. The findings indicate that such early bright light exposure seems to be sufficient to offset the effects of both limited sleep reduction and early awakening.

Circadian rhythms, sleep and wakefulness in a normal environment are discussed. The 24-hour daily cycle occurs as a result of both internal and external cues in the environment. However, if the individual is isolated from the normal environment, the circadian rhythm changes to a natural, "free-running" 25-hour cycle. It is hypothesized that with insomnia and other sleep disorders, there may be something wrong with either the entrainment or innate oscillation mechanisms so that the individual is unable to oscillate in synchrony with the environment.

This article indicates that most psychiatrists and psychologists have viewed circadian rhythms simply as periodic fluctuations in biological processes. Yet, alterations in social arrangements caused by shiftwork, together with circadian desynchronization, create a physical debilitation similar to that of endogenomorphic depression, with accompanying symptoms of weight loss, anorexia, anergia and irritability. What is unclear is whether the masking effects of neurophysiological functions, such as sleep and appetite, or of various hormonal and behavioral influences are themselves the causes of affective disorders or simply contribute to the circadian disorganization that itself creates such disorders. The author presents evidence that circadian desynchronization and the resulting dysregulation create affective disorders such as mania and depression.

The authors summarize circadian rhythms research, indicating that most bodily variables show circadian rhythmicity, usually with a daytime peak. These body rhythm patterns show little day-to-day variability in healthy individuals. The authors explain that circadian rhythms are primarily endogenous, or internally driven. They note clearly that changes in lifestyle alone, such as a change to a nightwork schedule, do not result in immediate changes in circadian rhythms.

This article describes the zeitgeber mechanism normally used to adjust or entrain the body clock to 24 hours. Moreover, it discusses the mechanisms for transmitting body time information throughout the body. The authors report that body temperature is correlated with metabolic rate, alertness and the ability to sleep.

This article summarizes the seven major studies on light effects in circadian system entrainment. The authors report that all of these studies demonstrated phase shifts as the result of bright light (>2500 lux) exposure. However, these studies do not conclusively identify the mechanism by which bright light produces phase shifts. What is notable is that bright light suppresses melatonin secretion, the hormone secreted by the pineal gland which induces sleep and creates a slowing of the EEG. Further study is needed to determine whether the effects of bright light on arousal are essential to the phase shift changes, or whether the administration of melatonin without bright light can produce the same phase shifts in the circadian system.

This book chapter provides a detailed overview of the factors involved in shiftwork. Shiftwork itself can be viewed as a stressor to the human body. Disruption of the circadian rhythms, which underlies our pattern of sleep and wakefulness, is a major consequence of shiftwork.

Performance is also affected by the desynchronization of circadian rhythms. The nature of the task must be addressed when studying efficiency and performance in relation to time or shift schedules.

In studying individual differences in terms of adaptation to shiftwork, it has been found that extroverts and/or evening types show the most rapid adjustment. The level of commitment to shiftwork adjustment also is an important consideration.

Circadian rhythm functioning and the effects on performance, sleep, and health are explained in this book chapter. Circadian rhythms run on a 25-hour schedule. However, with the help of zeitgebers, or time cues, minor corrections are made and the cycle adjusts to a 24-hour (day) cycle.

Research has found that the circadian rhythms are controlled by two, somewhat dependent oscillators: one which controls body temperature, and one which controls the sleep/wake cycle. It appears that task performance is related in some degree, although not exclusively, to body temperature, and that as body temperature declines, so does performance.

This scientific resource book provides an in-depth explanation of the circadian timing system and its specialized structures, mechanisms and functions. Noting that the specific structures that act as circadian clocks in the mammalian brain were not identified until 1972, the authors have compiled research on the impact of circadian rhythmicity from a range of disciplines. The circadian timing of such physiological systems as sleep-wake cycles, thermoregulation, endocrine rhythms and renal function are examined in detail, along with the medical implications of circadian rhythmicity

As the author states, "...for the human body, as well as for the human mind, timing is everything." This book provides a thorough explanation of all the timing systems in the human body. The chapter entitled "The Body in Hours" examines the function of circadian rhythms, noting that virtually every body function has daily peaks and troughs which are controlled internally. The function of the SCN and its link with the sun also are explained in clear terms. One word of caution for the reader: the author's explanations of sleep are only partially correct; see Horne's Why We Sleep for more accurate information on this important subject.

Data from the National Center for Health Statistics National Survey of Personal Health Practices and Consequences, which contained questions about sociodemographic characteristics, perceived health status, health practices, and whether the respondent had a variable work schedule, were analyzed to determine the impact of variable shift schedules on health-related behaviors.

A comparison between variable and non-variable shiftworkers revealed that males on variable shift schedules exhibited higher rates of heavy drinking, job stress, and emotional problems. Females on variable shift schedules reported higher rates of sleeping pill, tranquilizer and alcohol use, as well as more job stress, emotional problems and lower social network scores when compared to non-variable shiftworkers.

The data indicates that variable shiftwork was not associated with age, education or income level. Rates of heavy cigarette smoking and/or coffee drinking did not differ between variable and non-variable shiftworkers.

A general review of the literature regarding the health impact of shiftwork is included in this article.

This resource document contains papers presented during this two-day symposium on shiftwork and worker health. The overall question addressed in this paper is whether shiftwork is a significant health and safety problem. Topics covered by participating researchers included: a chronobiologic view of shiftwork and ulcers; an ergonomic and interdisciplinary approach to shiftwork and health; circadian rhythms in drug effectiveness and toxicity in shiftworkers; pharmacological and toxicological correlates of circadian synchronization and desynchronization; and accidents and injuries on shiftwork. Symposium participants concluded that shiftwork was, indeed, a significant health and safety issue.

This article gives a broad overview of the impact of shiftwork. Circadian rhythms are discussed, as well as sleep disturbances and performance effects. General health problems and effects on social and family life also are addressed.

This research study examines the efficacy of selected personality, behavioral and social/organizational variables as predictors of the subjective health of female night workers. Using experimental and control groups of nurses with no prior shiftwork experience, this study analyzed the impact of night work on physical and psychological health. The author found through a repeated measures design that the predictor variables change with the type of shift worked. For example, neuroticism and work/nonwork conflict predicted individual adjustment to a 2-shift (day and evening) rotation. Yet, social support from supervisors, neuroticism, rigidity of sleep and sleep duration predicted individual adjustment to a 3-shift rotation which involved night work.

The authors point out that individual differences in the ability to maintain alertness following inadequate sleep could be of great importance for the selection of shiftwork personnel in sensitive positions (e.g., chemical plant operators). Their study with Swedish males between the ages of 19 and 30 subjected to 64 hours of sleep loss revealed that resistance to performance decrement was highly related to adrenaline levels as well as to the range of adrenaline. These findings demonstrated that subjects with high resting levels of adrenaline and more marked circadian amplitudes degrade less due to sleep loss than their counterparts with lower levels. Such performance differences were not due to physical activity, since no correlation was found between performance and adrenaline.

The author hypothesizes that several external and internal factors, in addition to documented differences in the human circadian system, may be responsible for the individual degree of nightwork tolerance. Specifically, external factors such as social support, housing conditions (undisturbed sleep), work satisfaction, workload, leisure and eating habits, and seasonal influences are identified. Numerous internal factors also are discussed; namely, age, state of health, gender, personality type (extroversion-introversion), neuroticism and sleep cycle properties are specified.

In studying interindividual differences in circadian rhythms among computer operators, this research found that the night shift was the most difficult from the point of view of employee adjustment. The night shift was followed by the morning shift with the least difficult shift, in terms of adaptability, being the afternoon shift. This research also reported that night people, or "owls", had the least difficulty adjusting to shiftwork initially, and that "larks", or morning people had the most difficulty adjusting.

Differences in decreased performance or affective disorders of healthy adults exposed to circadian desynchronization indicates that some internal factors must be involved. The authors posit that non-tolerant shiftworkers must have weaker internal synchronization and/or be more sensitive to desynchronization effects. Moreover, they present the theory that iterative or repeated manipulations in zeitgebers, similar to the changes resulting from shiftwork, act to weaken internal synchronization and contribute to greater circadian desynchronosis.

The authors acknowledge that there are significant interindividual differences in tolerance to shiftwork. Their study is designed to identify variables which will predict which individuals can and cannot tolerate shiftwork. The study involved young workers in a Yugoslavian oil refinery who worked on an 8-hour, Continental (2-2-3) shift system. The findings indicate that evening types, persons with a low ability to control arousal level, social non-conformists and languid-type workers tended to sleep less during the day-shift assignment. Workers with rigid sleeping habits tended to sleep less on both evening and night shifts. Moreover, extroverts tended to sleep less on the night shift across all three years of the study. Of significance was the fact that this study did not demonstrate a significant correlation between the amplitude of circadian rhythms and characteristics of sleep. The authors state strongly that such research needs to be extended for a longer period of time to reach conclusive results.

As the authors state, it is a generally accepted opinion that shiftwork is related to greater risk of health impairments, especially gastrointestinal disorders (Costa, et. al., 1981 and Koller, 1984) and morbidity due to cardiovascular diseases (Koller, 1983). This Austrian research study analyzes the destabilization theory of shift-related disorders, comparing shiftworkers to day workers and stable shiftworkers to unstable shiftworkers. The results demonstrate that shiftworkers, as a whole, are significantly less adjusted or more destabilized in the three spheres of work, family and sleep, as compared to day workers. Furthermore, the amount of destabilization in shiftworkers is correlated with age and accordingly with shift experience. There was a significantly higher degree of instability or poor adjustment in the 41-60 age group as compared to the 20-30 age group, demonstrating that the length of tenure on shiftwork does not have a positive influence on the stability or adjustment of shift employees.

This article addresses some of the negative consequences of poor shiftwork adjustment. Specifically, alertness and performance issues associated with sleep deprivation are reviewed, as well as the disruption of social and domestic life that results from shiftwork.

The authors present behavioral and cognitive techniques or interventions that may produce sustained alertness in the work environment, counteract the negative effects of sleep deprivation and as a result, enhance work performance and production. Some of these alertness maintenance techniques, which can result in long-term enhancement of employee productivity, are: well-timed work breaks; variation of assigned tasks; and knowledge of task results. Some additional workplace interventions, which are suggested for short-term alertness enhancement, include: sensory and kinesthetic stimulation, such as background music and moderate exercise; exposure to bright artificial light or sunlight; and physiological regulation, such as regulated respiration and effective eating habits.

Additionally, the authors examine possible approaches to offset the negative social consequences that result from shiftwork. They believe shiftwork impacts not just the employee, but the employee's family as well. For optimal performance levels by the employee, education of the shiftworker and the shiftworker's family regarding sleep hygiene, stress reduction, and social support is vital.

A three-year follow-up survey was given to 46 volunteers from the membership of a small union of government workers on rotating shifts. The results of the initial survey showed a decrease in sleep length while on the night shift, an increase in reports of difficulty in sleeping and napping when compared to day workers, and little satisfaction with work hours.

The results of the follow-up study indicated no significant differences on any of the variables when compared with the initial study. This suggests that these variables are fairly stable in experienced rotating shiftworkers, and that there is no real adaptation to shiftwork without targeted interventions to facilitate shiftwork adjustment.

This study reports the results of a longitudinal study on the subjective health of new shiftworkers in a Dutch wire mill examined five times over a period of 12.5 years. This study also compared the shiftworker group to a control group of day workers in order to determine the influence of shiftwork versus the normal aging process. The specific health areas examined were:

-- Subjective health
-- Psychoneurotic complaints
-- Functional somatic complaints
-- Fatigue
-- Disturbed appetite
-- Digestive symptoms

Measures taken in 1972, 1973, 1976, 1979 and 1984 revealed a statistically significant deterioration in all areas of health across the first seven years of the study. Increased levels of fatigue were particularly significant during this period. Notably, these reported health impairments stabilized between the seventh and twelfth years, indicating that continued shift experience did not enable workers to improve their health status. Moreover, comparisons with the control group of day workers indicated that these shiftworkers had statistically significant more health impairments. In particular, shiftworkers had more functional somatic complaints, daily cumulative fatigue, habitual or chronic fatigue, appetite disturbances and digestive complaints than their counterparts who always had worked the day shift.

Using the Three Mile Island accident as an example, the authors emphasize that the study of shiftworkers' performance is a vital issue affecting public safety as well as the efficiency and effectiveness of many business and industry operations. They further emphasize that assessments of the impact of shiftwork on worker's productivity is one of the most complex problems facing researchers. This complexity is due to the multitude of factors influencing shiftworkers' performance: nature of task demands and circadian oscillatory control, time-of-day effects, sleep deprivation effects, motivation effects and interindividual differences in circadian timing.

From repeated studies on this topic, the authors believe that lifestyle adjustment effects influence the worker's on-shift performance most directly. Countermeasures for improving performance must take into account many factors associated with the job and its constraints, and with the employee and his/her situation and needs. The authors state emphatically that one cannot select the optimum shift system without a thorough knowledge of the tasks to be performed.

A description of the methodology used to study circadian rhythms is discussed in this paper along with the research findings from sustained performance experiments and the implications of these findings for future experiments.

Included in the background research are the findings of "free-running" experiments in which the subject selects the timing of rest, activity, and meals. These studies indicate that the circadian rhythms run on a 25-hour cycle when not disrupted by other time cues. Desynchronization occurs when the cycles of sleep/wake and temperature break apart, running at different periods. Desynchronization is important because it indicates that the sleep/wake and the temperature cycles are under the control of two separate, but interactive oscillators. Recent research findings indicate that these mechanisms underlying circadian performance rhythmicity have important ramifications in the sustained performance situation.

Included in the methodology of circadian rhythm research are: facility set-up, including meal and sleep coordination; computerized data collection; performance and mood assessment, including subjective alertness, performance sessions, search tasks, mood, and practice effects.

This study was designed to produce a desynchronization in the two oscillators underlying the circadian cycle in order to assess directly the behavior of the rhythms in regard to different performance tasks. The findings of this study indicate that simple manual dexterity tasks are almost entirely under the control of the temperature rhythm oscillator, while the more complex cognitive tasks including alertness-related performance, appear to be under the control of both the temperature and the sleep/wake oscillators.

This study was conducted to determine the effects of shift rotation direction, and the speed of return to work after a shift change. A large pool (N=261) of shiftworkers from a range of British industry and service organizations took part in the study. The Standard Shiftwork Index, a set of questionnaires, was used to gather the data. Results indicated that the forward (delayed) schedule showed more statistically favorable outcomes with regard to sleep disruption. Also, a quick return to work appeared to show less favorable results. The authors concluded that the study supported the building evidence that forward rotation is a preferred schedule characteristic, but, most certainly, a backward rotation with a quick return between shifts should be avoided.

The relationship between individual control of hours of work and tolerance of shiftwork was examined in a group of nurses and midwives. The Standard Shiftwork Index, a set of questionnaires, was used to gather the data. In general, the results of this study were that a greater tolerance toward shift work was associated with shiftworkers having control over the hours of work. This lends support for the notion of employee participation during the work schedule design process. These authors also argue that the highest level of satisfaction was achieved by those choosing to work a continuous nightshift.

This book is designed to help organizational leaders work in a way that better meets the needs of both the organization and individual employees. The authors examine the forces affecting the choices of alternative work schedules and the advantages and disadvantages of different options. A model linking career and life-cycle stages to work attitudes is presented along with a model for managers to use in choosing appropriate time arrangements in their workplace.

The authors present a framework to match the cyclical time demands for work with people and with schedules in a way that leads to better coverage of work needs, greater commitment of employees, better utilization of human resources, and greater productivity. This framework is known as the DIPS method of scheduling (Demand People Schedules) and is intended to connote cyclical fluctuations. Fourteen guidelines for schedule selection are provided.

This paper discusses the general trends, advantages and disadvantages, and variations of compressed workweeks. Social demands for increased leisure time and the need for longer work shifts in certain industries have spurred an interest in extended work hours. Factors influencing extended work hours include the type of work performed, the size and structure of the organization, and existing management-labor agreements. Twelve-hour shifts are considered the most compatible for continuous operations.

This study examines the effect of days on and days off duty within a permanent night shift schedule. Two groups of female nurses (N=78) were studied. One group worked a slowly-rotating schedule ("many night group") with 5 to 8 nights on and 5 to 8 nights off (N=42) and the second group worked a so-called rapid-rotating schedule ("few night group") with 1 to 4 nights on and 1 to 4 nights off (N=36). It is important to note that the subjects' acceptance of permanent night work was the result of "motivated choice". The following data was collected for the study:

-- Biographical Information -- Social Support -- Work Situation -- Lifestyle -- Job Satisfaction -- Risk Factors

-- Family Situation -- Evaluation of Night Work -- Subjective Health -- Coping Mechanisms -- Sleep Complaints

From the processed data, the author concluded that both groups had adapted reasonably to their shift schedule. No significant differences were found in subjective health or in job satisfaction between the two groups. Minor differences between the two groups which were noted focused primarily on the "many night group." A higher percentage of the "many night group" smoked cigarettes and drank alcoholic beverages. Additionally, more nurses working on the slowly-rotating schedule participated in sporting events and used more adaptive behavior to prevent stress. The author concluded that the differences between the two schedules were not significant enough to favor one over the other.

Key to a critique of this study is the knowledge that rapid-rotation designs are defined as a shift system with no more than 3 consecutive night shifts followed by at least 48 hours off (Knauth, Ergonomics, 1993, pp. 15-28 and Knauth & Rutenfranz, Journal of Human Ergology, 1982, pp. 337-367). Thus, the study findings have to be viewed as invalid or inconclusive in that the "few night group" included individuals with four consecutive night shifts as well as individuals with only one day off between their shifts.

This document reports on the results of a study involving shiftworkers, non-shiftworkers and former shiftworkers. A comparison was made between different shift schedules with regard to ill-health (stress at work, psychological and psychosomatic complaints). The number of participants was broken down as follows: 1,295 night and rotating shiftworkers with an 8-hour schedule, 1,198 night and rotating shiftworkers with a 12-hour schedule, 693 non-shiftworkers, 123 former shiftworkers who left due to health reasons, and 98 former shiftworkers who left for reasons other than health (e.g., better job). The total sample included 3,407 male, blue-collar chemical workers from 24 factories in West Germany.

There was no significant difference between the 8-hour and 12-hour schedules when stress, age and skill level were controlled.

This relatively comprehensive review article of research on shift schedules begins by stating, "All shift systems have advantages and drawbacks. There is no single 'optimum shift system' which can be used in industry or commerce at all work places. However, there are shift systems which are more favorable, and others which are less favorable, in the context of physiological, psychological, and social recommendations for the design of shift systems." (p.15)

Based on the research reviewed in the article, the author makes the following recommendations for shift design:

1. Night work should be reduced as much as possible, or rapid rotation should be used when needed. Slow rotation and permanent night shifts are not advised.

2. Extended workdays of 9 to 12 hours should only be used if the nature of the work is suitable. Further, where extended workdays are used, accumulated fatigue should be minimized through limited days-in-a-row.

3. An early start for the morning shift should be avoided.

4. Quick changeovers between shifts must also be avoided.

5. Consecutive days should be limited to 5 to 7 days. Additionally, schedules should include some free weekends.

6. The forward or clockwise rotation of shifts appears to be the recommended approach for continuous shift schedules.

Shiftwork systems can be categorized as: 1) permanent shift systems with single permanent shifts, multiple permanent shifts, and split shifts at constant times; and 2) rotating shift systems including continuous and discontinuous systems without the night shift and continuous and discontinuous systems with a night shift. Within these basic categorizations, many variations in shift system design are possible.

The characteristics of shiftwork schedules include: the number of consecutive night shifts; start and finish times; the duration of the shift and the shift cycle; the distribution of leisure time; and the regularity of the shift system. In this article, these characteristics are discussed with regard to research findings on physiological adaptation, performance and accidents, well-being, health, and personal and social problems.

In review of the research regarding shiftwork systems, Knauth and Rutenfranz put forth nine recommendations for the design of shift systems: 1) The shift system should have few night shifts in succession. 2) The morning shift should not begin too early. 3) The shift change time should allow individuals some flexibility. 4) The length of the shift should depend on the physical and mental load of the task, and the night shift could be shorter than the morning and afternoon shifts. 5) Short intervals of time between two shifts should be avoided. 6) Continuous shift systems should include some free weekends with at least two successive free days off. 7) A forward rotation is preferred for continuous shift systems. 8) The duration of the cycle should not be too long. 9) The shift rota should be regular.

The evaluation of conversions to a 12-hour shift schedule in 15 companies is the topic of this research article. Personnel executives from petroleum and chemical facilities were sent surveys which inquired as to the efficacy of the conversion, from the business and employee perspective. This 8-year follow up study produced results which indicate an overwhelming success in the conversion to 12-hour shifts. Absenteeism dropped, safety was unaffected, costs were reduced (primarily due to less overtime), an increased effectiveness in communication was observed, and employee job satisfaction increased.

This study looked at worker attitudes regarding three rapidly rotating shift systems. In two of the systems, the shift period was comprised of 7 consecutive working days with 2 or 3 days on the same shift, differing only in regard to the number of free days after the shift period -- 2, 3, or 5 days. The third schedule was a 3x3x3 rota followed by 3 days off. For comparison, two groups of employees on intermittent 3-shift schedules were included.

Two of the three groups with rapidly rotating shifts were as satisfied with their shift schedules as workers on the intermittent 3-shift schedule. Employees with only two days off were relatively unsatisfied with their schedule, mainly because they disliked the distribution of work time and free days off. It appears as though the length of the break between the shifts may be an important factor in determining the attractiveness of rapidly rotating shifts.

Social, technical, and economic reasons contribute to the necessity of shiftwork in certain industries. Different types of shiftwork, its effects on health (sleep and digestion), re-entrainment problems, and the disruption caused to family and social life are reported.

The criteria for optimal shift schedules include: 1) single night shifts being better than consecutive night shifts; 2) at least 24 hours time after each night shift; 3) the cycle should be of a short duration; 4) the length of shift should be related to the type of work; and 5) for continuous shiftworkers, as many free weekends as possible should be arranged.

This paper supports the idea that shiftwork should be tailored to each individual site or plant. One way to achieve that end is by the survey method which ensures that worker preferences and needs are evaluated and presented to management before shift schedules are devised. Factors to consider when evaluating shift system changes include: age of workers, gender, marital status, sleep habits, hourly/salary status, and employees' shift schedule preferences.

The beginning of this book chapter presents shiftwork terminology and a notation method for work schedules. A variety of different schedules are included to show the diversity of design possibilities. The authors stress the importance of considering the range and complexity of human factors that can be affected by a particular schedule. They also emphasize that all workplaces are not the same; a schedule that can improve worker productivity and health for one workplace might diminish the same factors in another workplace.

Key components of the work schedule, such as speed and direction of rotation, should be addressed prior to selection and implementation. Regardless of the rate of rotation chosen, it is generally recommended that the rotation of the shift be in a forward direction. This allows for easier adjustment to the new shift, since it follows the body's natural circadian cycle.

Educational programs should always accompany schedule changes or new system implementation. These programs should explain the schedule to those involved in it so that they understand the system, know what to expect, and understand the rationale for it. The programs should also provide the workers and their families with information which can help them in cope with the work system in a more effective manner.

This article investigated a number of companies that had converted to 12-hour shift schedules. Companies cited include Dupont, Bridgestone/Firestone, Raritan River Steel, and AMAX Coal. The focus was on the positive attributes of the 12-hour shift alternatives, and the success that the companies had making the conversions. Productivity and safety have improved as a result.

Recommendations for making conversions to 12-hour work schedules included starting with the management decisions to make the change, involving employees in the decision making, and testing the change before making a complete conversion. As reported by these companies, the primary drawback to a 12-hour schedule involved communication. It can take over a week before every employee can receive required information, due to the longer periods of offtime.

The general population does not fully understand that the level of human alertness in the daytime is inevitably and solely linked to sleep at night. Yet, "sleepiness" sensations during the daytime are caused by physiological factors other than the quality and duration of night sleep. Humans develop a marked tendency toward sleepiness in the middle of the day from adolescence onward. Nature definitely intended that adults should nap in the middle of the day, perhaps to get out of the midday sun. This comprehensive book on napping examines the subject in detail, exploring such important topics as the ultradian aspects of napping, napping and human functioning during prolonged work, and shiftwork and napping. This latter chapter by Akerstedt, et. al. examines the related benefits and disadvantages of napping while on night-shift assignments, which is very common among shiftworkers.

This study documents that night and early-morning shifts lead to shortened sleeping hours. Overall sleeping time was not found to be different for workers on different shift schedules. Moreover, length of sleep was not predicted well by factors such as stress at work, noisiness of sleeping room, drinking coffee, and smoking cigarettes, although these and similar predictors were strongly related to quality of sleep. Shiftwork was found to have a consistent effect on quality of sleep, even when other variables were controlled.

The author explains that human sleep is governed by two mechanisms -- the obligatory requirement for brain restitution, and the facilitatory sleep mechanism governed by circadian influences. Obligatory or core sleep occupies the first part of sleep, making this the most critical. The author also reports that physical tiredness due to shortened sleep is not due to the loss of the restitutive benefit of sleep, but rather produces a decline in motivation to perform. Such tiredness is manageable by methods other than obtaining more sleep. However, loss of obligatory (core) sleep produces central nervous system impairment and diminished brain functioning.

This book is considered to be the most definitive work on human sleep. The author explains sleep architecture, and also provides an exhaustive survey of the research on sleep deprivation. The impact of sleep on cerebral (brain) and body restitution are examined in detail. Moreover, the author explains the difference between core sleep and optional sleep, indicating that the first five hours of sleep are the most crucial to human alertness and effective brain functioning.

This work explains in clear terms that sleeping patterns have a direct influence on waking behavior, and, in turn, daytime habits influence sleep quality and duration. The purpose of this book is to provide consumers with a clear understanding of scientific sleep research and explain what steps can be taken to improve sleep. The section on better sleep provides specific strategies for getting a better night's sleep and for handling unexpected disruptions in a sleep episode. This book is general in nature, so it does not include specific strategies for shiftworkers faced with daytime sleep schedules. Moreover, it does not include the most recent, breakthrough research about sleep.

This article underscores the fact that humans can alter their sleep temporarily, but they always return to a sleep "budget" that seems genetically fixed. Noting that, after the common cold, difficulty with sleeping is the most prevalent health complaint, the author explains that there are more than 50 different documented sleep disorders. The article indicates that sleep architecture was first documented in the 1950s with the discovery of REM (rapid eye movement), or dream sleep, making modern sleep physiology a relatively new field of science. Dr. William Dement, a leading sleep researcher, is cited for his findings that humans deprived of REM sleep can rebound and make it up later, while deep (core) sleep seems to be lost forever.

The authors examined the length of the period in which after-effects in the subjective sleep quality following night shifts can be measured. They found that the older the workers, the longer their complaints persisted. Knowing that sleep quality deteriorates with age, they found that older shiftworkers sleep one to two hours less per day, on average, than younger workers. Moreover, they documented through three different studies that the after-effects following sleep/wake desynchronization from seven (7) consecutive night shifts are still measurable with respect to sleep quality during the second undisturbed recovery night. These authors conclude that the common recovery period of two to three days off after an extended period of night shifts is probably too short. This results in shiftworkers starting their next shift assignment in sub-optimal condition. The authors also report that an accumulation of fatigue results from this incomplete recovery, creating the chronic fatigue commonly reported by shiftworkers.

Nightworkers typically manifest a workday reduction in sleep length and decrements in performance like those of people suffering from chronic sleep deprivation. This article reports average sleep times of shiftworkers, which can be used as a data base for gauging the need for intervention. Additionally, the workday and offday sleep habits of permanent night shiftworkers are studied in detail. The authors conclude that most permanent night employees use sleep strategies which, in effect, place them on rotating shifts. In fact, they argue that the frequency of the changes in sleep strategies between workdays and offdays make "permanent" night assignments "perhaps the worst possible rotation schedule."

This study examined the sleep and performance of male shiftworkers assigned to a weekly rotating, three-shift system. With respect to sleep, the authors found that day sleep was shorter in duration, degraded in quality, and its sleep stages more temporally disrupted. Moreover, they concluded that the deterioration in performance across night shifts is due to an accumulative sleep deficit. Thus, they argue that rapid or shorter rotation cycles are a better shift system in that they prevent this sleep deficit from occurring.

The authors note that the health consequences of acute and chronic sleep loss have been poorly documented. This change reviews laboratory and field studies on this topic, covering three primary kinds of sleep loss: total, selective and partial. They note that the most critical form of sleep loss for occupational medicine practitioners is chronic partial sleep deprivation -- loss of several hours of sleep repeatedly every day over many days -- the type of sleep deprivation most common among shiftworkers. They report that, for workers needing maximum alertness and uninterrupted concentration (air traffic controllers, heavy equipment operators, power plant and chemical plant operators, etc.), anxiety about the effects of chronic partial sleep deprivation is warranted. Such deprivation can cause lapses of attention and inability to concentrate.

This article provides an overview of the ways in which shiftwork has been found to affect individual, social and family lifestyles. Comparisons across different types of shift assignments reveal that the fixed afternoon or evening shift has the highest levels of social complaints and the least satisfaction with the work schedule. Conversely, permanent night-shift workers and their spouses report few social and family problems, and generally have a higher rate of participation in organizational activities than any other shiftwork group. Unfortunately, there is some evidence that the fulfillment of family obligations may be accomplished at the physiological cost of lost sleep by nightworkers.

The research also indicates that, while rotating shiftworkers may have more flexible time for social and family activities relative to other shiftworkers, feelings of lethargy and general malaise may reduce their ability to use this time effectively. One final note concerns shiftworkers in continuous (7-day) operations. A number of studies have indicated that weekend work is the most dissatisfying aspect of shiftwork. It has been found to result in less time per week with children and a poorer quality of family life. In conclusion, each shift produces a set of advantages and disadvantages in terms of social satisfaction and adjustment for the worker and his/her family. The authors suggest further research on this topic, with more objective indicators of social and family adjustment and broader types of workers.

The authors explain that the psychosocial consequences of shiftwork are more problematic for some workers than the acquisition of physical illness. The evidence clearly indicates that shiftworkers are less satisfied with the time available for family and friends and report a lower quality of family life than dayworkers. This study examines the extent to which shiftwork experience helps to remedy these social and domestic problems. The authors found no change in psychosocial well-being in an experimental/control study across a three-year period. In the absence of any improvements, the author concludes that experience alone does not promote positive psychosocial functioning. Targeted interventions are advocated, including lifestyle education and individual counseling.

Shiftworkers' perceptions regarding the degree to which their leisure activities are affected (positively or negatively) by shiftwork schedules were addressed in this study. The results indicated that workers rated time-flexible activities as being less hindered by the shift schedule than were inflexible activities. Among those activities regarded as more hindered (inflexible) were: sleep, meals, interaction with the family, interaction with others, watching sporting events, watching T.V. and listening to the radio. Housework, shopping, errands, maintenance of house and garden and child care were among those reported to be less hindered (flexible) by the shift schedule. The group of workers who had quit the job by the end of the two-and-one-half year period reported a greater number of hindered activities than those who stayed on the job.

With the exception of one or two articles, the issue of employee wellness programs with regard to shiftwork has been virtually ignored. This may be a result of many factors, including: the fact that most administrators do not work evenings and night shifts, and are therefore less likely to experience the impact of shiftwork on wellbeing and family life; and, that research on the relationship between health and shiftwork is often confusing to even the most informed reader.

Research conducted by the authors regarding the cause-and-effect relationship between shiftwork and wellbeing reveals some interesting findings, which include:

1. Evidence that one spouse's work schedule has a ripple effect upon the entire family, and that if that effect is negative, the family is often a less effective buffer for the worker's psychological stress.

2. A study of nurses found no direct link between shiftwork and the existence of work/family problems. Rather, night and rotating shifts were related to stress symptoms. It was these stress symptoms that were then related to work/family problems.

3. This same study found that, for some nurses, shiftwork was viewed as a solution to combining work and family roles. Oftentimes, shiftwork was chosen as a way to resolve work/family problems rather than viewing it as problematic to the family.

This article focuses on the problems associated with two-shift operations rather than round-the-clock organizations. The author reports that absence due to sickness is higher among two-shift employees than three-shift workers. Moreover, his research reveals that employees in two-shift operations experience social difficulties, such as child care, family life and leisure-time activities, which are just as or more severe than three-shift workers. In fact, over half (51%) of the two-shift workers included in this study reported problems with family relations due to their work schedule as compared to 38% of the three-shift workers. Similarly, 42% of the two-shift employees had problems arranging leisure-time activities with their family, as compared to 31% of the three-shift employees. Social difficulties seem to be closely related to collisions between the work hours and the time schedule of social life. Second-shift workers seem to encounter more of these collisions. The author concludes that working hours become more of an obstacle to social and family life the more the desired leisure activity is set at a fixed time and the greater the degree of coordination required with other people's schedules. The results of such social difficulties include: family problems become severe; one's circle of friends becomes restricted; and some leisure activities are dropped.

This book chapter examines the issues raised by work schedules (pattern of days, pattern of hours, and number of hours) and work-family conflict in two-earner families. Work-family schedule conflict can take one of two forms: 1) job-family scheduling conflict, i.e., incompatibilities between an individual's job and family schedules; or 2) job-job schedule conflicts, i.e., conflicts directly between or indirectly generated by the two spouses' job schedules. A distinction between one- and two-earner families can be made with regard to the two types of conflict noted. A two-earner couple can exhibit both types of conflicts, while the one-earner couple can encounter the job-family scheduling conflict. Spouses' job schedules can be either similar, unrelated, or complementary. Schedules may be arranged to either overlap or coincide for any number of reasons.

The author reports that the social problems of shiftwork have not been based on any theoretical background. He proposes to use "social time," and the value which is attached to different times of the day and days of the week, as a construct to be used in research on the social and domestic consequences of shiftwork. From this perspective, he analyzes the effects of shiftwork on the domestic life of both the shiftworking and non-shiftworking spouse. Emphasis is given to role fulfillment issues among shiftworkers, including roles as sexual partner, spouse and parent. With regard to social effects, the author notes that the degree of social problems are influenced by the individual personality and leisure preferences of shiftworkers, as well as the kind of community where they live. Time-flexible activities are considered more compatible with shiftwork schedules than time-inflexible or organizational events.

This ground-breaking study addressed four main areas related to the social aspect of shiftwork schedules. These include the incidence of complaints, the severity of social effects, the relative importance of different activities, and the interaction of physical and social effects of shiftwork.

Results obtained from a survey of British steel workers on non-day shifts indicate that their biggest single complaint was about their social life, followed by complaints of irregular sleeping times, meals and health effects.

Those activities in which workers reported feeling "worse off" because of shiftwork include, in descending order: weekends, a full social life, watching sports, participating in social organizations, planning social engagements, and following a regular T.V. series. Most of these complaints have to do with specific time-related activities. Those activities reported as "better off" include: freedom in the day time, time for yourself, variety in working hours, and pay.

This study concluded that the interaction of physical and social effects is important in balancing the advantages and disadvantages of shiftwork. The advantages of higher pay and more free time can be outweighed if there is desynchronization of circadian rhythms due to interrupted sleep.