Lawrence Smith

The impact of early and late shift changeovers on sleep, health, and well-being in 8- and 12-hour shift systems.

The effects on industrial shift workers of the timing of the changeover from the night to morning shift and of the length of the shift were examined. Two groups changed over at 6 a.m. and worked either 8-hr or 12-hr shift systems; the other 2 groups changed over at 7 a.m., working either 8- or 12-hr systems. Night sleeps between consecutive shifts that started at 6 a.m. were shorter and more disrupted than those starting at 7 a.m. Day sleeps following night shifts that finished at 6 a.m. were longer and less disrupted than those finishing at 7 a.m. Early starts were associated with poorer psychological and physical health. These effects of changeover time are considered in relation to the circadian rhythms in sleep duration and propensity. Although several measures favored 12-hr shifts, physical health indicators appeared to favor 8-hr systems, especially in combination with late changeovers. However, the observed effects of shift length on chronic outcome measures are somewhat inconsistent with previous research findings.

Investigating effort–reward imbalance and work–family conflict in relation to morningness–eveningness and shift work

Abstract The effort–reward imbalance model (ERI; Siegrist, 1996) has been found to be a strong predictor of both psychological and physiological outcomes. Morningness–eveningness (M-E) is believed to relate to shift workers’ ease of adjustment to irregular working patterns. However, it has not been investigated in conjunction with the ERI model. The present study (1) explored whether M-E acts as a predictor of psychological adjustment to shift work, above and beyond the contribution of the ERI model and (2) examined whether the formulation of the ERI model may be overly complex. A sample of police employees (N=112) completed a baseline questionnaire that contained the ERI model and a measure of M-E. Two months later, participants completed measures of work–family conflict and burnout. Regression analyses demonstrated that ERI was a significant predictor of psychological adjustment to shift work. Moreover, and for the first time, M-E was found to make a unique contribution to the prediction of work–family conflict, such that evening types reported greater levels of maladjustment. However, it did not make a unique contribution to the prediction of burnout. The possibility that the ERI model is unnecessarily complex received partial support, with the ratio score only contributing additional variance in one of four regressions. The results indicate that adjustment to shift work and attendant effects on work–family conflict can be affected by an individuals morning-evening typology.

The Impact of Rest Breaks on Temporal Trends in Injury Risk

This study examined the impact of rest breaks on temporal trends in industrial accident risks in an attempt to replicate earlier findings of a linear increase in risk as a function of elapsed time on task. In two separate studies, the trend in work‐related injuries were studied in relation to the timing of rest breaks. In study one, comparisons were made between on‐ and off‐track workers on weekly rotating three‐shift systems operating in a large engineering company. Records of on‐duty injuries that occurred over 12 months were examined (N=4645 incidents). Study two involved interviewing patients who had suffered work‐related hand injuries in a variety of occupational settings (N=407 patients). Hierarchical log linear analysis was used in both studies. In study one, risk increased from the first to the second half‐hour of continuous work following a break, but then remained relatively constant in subsequent half‐hour periods, although there was a fall in the third half‐hour for on‐track workers. In some of the data, there was also a decrease in risk in the period leading up to the end of a work period. There was a sharp decline in reported injuries toward the very end of a shift, but otherwise the observed trends did not differ between successive periods of continuous work or between morning, afternoon, and night shifts. In study two, risk increased from the first to the second half‐hour of continuous work and then remained relatively constant in the third half‐hour. The contrast between the current and previous findings may be due to the relatively unique work environment of the previous study. It is suggested that the current trends reflect the effects of working in a relatively unconstrained task environment, and that causes other than fatigue may underlie the trends observed in both the previous and current studies.

The influence of morningness–eveningness on anxiety and cardiovascular responses to stress

The relationship between cardiovascular responses to stress and health outcomes is inconsistent. In this study, the effects of morningness-eveningness and time of day upon cardiovascular activity at rest and in response to stress were examined. Sixty morning-types and evening-types completed two testing sessions (one morning, one afternoon) that comprised a battery of three stress tasks and a measure of anxiety. The results failed to support a time of day effect upon cardiovascular activity, but there was evidence of an interaction between time of day and morningness-eveningness upon heart rate (HR) and rate pressure product (RPP; HRxSBP). Evening-types exhibited higher HR and RPP in the afternoon, both at rest and during stress. A time of day effect was shown for mood, with anxiety levels higher in the morning than the afternoon. These results are discussed in terms of their health and methodological implications.

Industrial shift systems

This technical report describes the identification of shift systems worked by industrial shiftworkers in England, Scotland and Wales. A diverse range of shift systems were reported to be in operation across 27 industrial sectors. Companies employed up to 14 different shift systems at a particular site. The numbers of shiftworkers on a given shift schedule ranged from 1 to 2977. Most systems employed fewer than 100 people. The majority of rotas were regular, rotating systems. The most common shift durations were 8 or 12 h. Compared to earlier surveys of shiftwork prevalence in certain industries there appeared to be a substantial increase over the past 3 decades in the proportion of the workforce who work shifts. Information about the average numbers of hours worked per week on major system types is given. In addition, data for the range of shifts per cycle, the distribution of shifts and distributions of their start and end times are presented.

Demands, resources, and work ability: A cross-national examination of health care workers

Understanding work ability, with the goal of promoting it, is important for individuals as well as organizations. It is especially important to study work ability in health care workers, who face many work-related challenges that may threaten work ability. We studied various job demands, job resources, and interactions of demands and resources relating to work ability using the Job Demands–Resources model as a framework. Acute care health care workers from six nations (US, Australia, UK, Brazil, Croatia, and Poland) completed a survey. Role demands related to work ability in the Australia sample only, and supervisor support related to work ability in the Australia sample only. Yet, high levels of supervisor support significantly moderated (buffered) negative relationships between physical demands and work ability in the US sample, along with negative relationships between role demands and work ability in both the Croatia and UK samples. Skill discretion related to work ability in every nation sample, and therefore appears to be particularly important to work ability perceptions. In addition, skill discretion moderated (buffered) a negative relationship between role demands and work ability in the Australia sample. We therefore recommend that interventions to help preserve or improve work ability target this important job resource.

Internal locus of control and shiftwork effects

A range of situational, biological and psychological individual differences have been suggested to modify the impact of shift and night work. This paper discusses the development and application of a construct firmly based in the psychological/behavioural domain. The overall aim is to offer a theoretical standpoint with practical implications. Locus of Control theory has an extensive research history. In line with the evolution of thinking about this construct in terms of application in a context-specific sense, this paper describes the origins of internally-oriented Shiftwork Locus of Control (SHLOC) and presents its relationships with typically reported shiftwork-related outcomes. The SHLOC measure has been shown to be psychometrically robust and has demonstrated consistent patterns of relationships with shiftwork related variables that include sleep quality, fatigue, alertness, interference with family and social life, psychological well-being and perceived stress. In general, higher shiftwork-specific internality is associated with more positive outcomes (e.g. better sleep quality, lower fatigue, higher alertness) than lower shiftwork-specific internality. These findings hold true across a range of shiftwork situations and occupational groups. The construct has practical potential as an addition to shiftworker monitoring procedures that may be used to identify those individuals who may be more susceptible to the negative effects of shiftworking and, thereby, could benefit from targeted intervention.

DAYTIME INTERMITTENT BRIGHT LIGHT EFFECTS ON PROCESSING OF LATERALLY EXPOSED STIMULI, MOOD, AND LIGHT PERCEPTION

Little is known about intermittent bright light (IBL) exposure during the daytime on oscillations in human performance and mood. The aims of this study were to determine whether the applied regime of IBL can differentially influence the daily oscillations of processing of laterally exposed stimuli, as well as the daily course of alertness and affective state, and the participants perception of light conditions. A counter‐balanced, within‐subject study design was applied. Performance and mood of 20 student volunteers were measured every 30 min starting at 08:00 h and ending at 20:30 h in IBL and ordinary room light (ORL) conditions. Near to statistical significance, effects of the IBL regime on performance (i.e., main effect on speed of verbal logical task, and interactive effect of light conditions and measurement time on daily oscillations in speed of processing of spatial tasks) and mood (i.e., interactive effect of bright light and measurement time on global vigor assessment) were found. An assessment of IBL conditions as significantly less comfortable and natural and more glaring when compared to ORL conditions draws attention to the importance of participants perception of the light, which may affect the application of bright light in real life situations.

Bright light effects on ultradian rhythms in performance on hemisphere-specific tasks

Ultradian rhythms in indices of brain hemisphere activity and in cognitive performance have been found in numerous studies. Asymmetry of these rhythms with regard to phase and frequency have also been documented in some studies. There is some evidence that bright light can affect ultradian rhythms of arousal state and vigilance. A study on unilateral exposure to bright light has demonstrated more pronounced effects of bright light on the right hemisphere. The aim of this study was to examine whether daytime intermittent bright light could affect parameters of ultradian rhythms in performance speed on hemisphere-specific tasks, and whether the effect of bright light was symmetric for the rhythms in performance on hemisphere-specific tasks presented laterally. A counter-balanced, within-subject research design was applied. The performance of 15 participants on hemisphere-specific tasks exposed laterally was measured every 30 min starting at 08:00 h and ending at 20:30 h in intermittent bright light (IBL, pulses of 15 min of 4000 lux light regularly interspersed between 45 min of background light levels of 300 lux) and in ordinary room light (ORL) conditions (300 lux). Individual time series data were subjected to cosinor analysis. General linear model analyses (the factors were: level of processing, visual field, and the task) were performed on the rhythms parameters. There was a substantial lengthening of the rhythms periods in IBL conditions for performance speed on spatial tasks and an increase in amplitude of the rhythms of performance speed for spatial tasks in both visual fields and for verbal tasks in the left visual field in the IBL conditions when compared to the ORL conditions. The results showed that the schedule of light exposure affected ultradian rhythms of hemisphere-specific tasks differently and that the right hemisphere seems to be more sensitive to light than the left hemisphere.

Shift schedule, work-family relationships, marital communication, job satisfaction and health among transport service shift workers

OBJECTIVESnExisting research has documented that shiftwork consequences may depend on the shift system parameters. Fast rotating systems (1-3 shifts of the same kind in a row) and day work have been found to be less disruptive biologically and socially than slower rotating systems and afternoon and night work. The aim of this study was to compare day workers and shift workers of different systems in terms of rotation speed and shifts worked with regard to work-family and family-work positive and negative spillover, marital communication style, job satisfaction and health.nnnMATERIAL AND METHODSnEmployees (N = 168) of the maintenance workshops of transportation service working different shift systems (day shift, weekly rotating 2 and 3‑shift system, and fast rotating 3-shift system) participated in the study. They completed the Work- Family Spillover Questionnaire, Marital Communication Questionnaire, Minnesota Job Satisfaction Questionnaire and the Physical Health Questionnaire (a part of the Standard Shiftwork Index).nnnRESULTSnThe workers of quicker rotating 3-shift systems reported significantly higher scores of family-to-work facilitation (F(3, 165) = 4.175, p = 0.007) and a higher level of constructive style of marital communication (Engagement F(3, 165) = 2.761, p = 0.044) than the workers of slower rotating 2-shift systems. There were no differences between the groups of workers with regard to health and job satisfaction.nnnCONCLUSIONSnA higher level of work-family facilitation and a more constructive style of marital communication were found among the workers of faster rotating 3-shift system when compared to the workers of a slower rotating 2-shift system (afternoon, night). This may indicate that the fast rotating shift system in contrary to the slower rotating one is more friendly for the work and family domains and for the relationship between them. Int J Occup Med Environ Health 2017;30(1):121-131.