Philip Tucker

The impact of rest breaks upon accident risk, fatigue and performance: A review

This reviews primary objective is to identify research examining the impact of rest breaks uponaccident risk in industrial settings. In the absence of much directly relevant research, the focus isbroadened to consider the impact of rest breaks upon performance and fatige, as well asepidemioogical evidence, in both transport and non-transport settings. Relevant studies are identifiedfrom a range of electronic sources. In general, regular rest breaks can be an effective means ofmaintaining performance, managing fatigue and controlling the accumulation of risk over prolongedtask perfonmance. While two-hourly breaks are common in many industrial settings, the scheduling ofadditional micro-breaks can be beneficial under at least some circumstances. While some evidencesupports allowing workers to take rest breaks that coincide with periods of heightened fatigue,workers sometims fail to take adequate breaks when they are needed. There is little hard evidenceconcerning the optimun length of rest breaks (other than for heavy physical work), or to support thecontention that increased rest-breaks can off-set the negative inpact of extending shift durations, or tosuggest that rest breaks counteract the neptive impacts of circadian variations in alertness, unless theyinvolve taking a nap or caffeine. The scarcity of epidemiological evidence in this area highlights theneed for more research.

Moderators of the relationship between long work hours and health.

The authors examined how associations between work hours and self-reported health are moderated by the reasons given for working overtime, by schedule autonomy, and by the degree of social support experienced, in a survey of 372 train drivers. Respondents who lacked both schedule autonomy and social support demonstrated positive associations between the number of hours worked per week and frequency of physical health symptoms. Conversely, negative associations were observed among respondents reporting low schedule autonomy together with high social support. There were no such interactions in the analyses of fatigue and psychological health outcomes. The findings are discussed in terms of the fit between an individuals actual and desired work hours. The problems of identifying appropriate limits for work hours are highlighted.

Beyond the Three-Process Model of Alertness: Estimating Phase, Time on Shift, and Successive Night Effects

This paper starts by summarizing the development and refinement of the additive three-process model of alertness first published by Folkard and Åkerstedt in 1987. It reviews some of the successes that have been achieved by the model in not only predicting variations in subjective alertness on abnormal sleep-wake schedules but also in accounting for objective measures of sleep latency and duration. Nevertheless, predictions derived from the model concerning alertness on different shifts, and over successive night shifts, are difficult to reconcile with published data on accident risk. In light of this, we have examined two large sets of alertness ratings with a view to further refining the model and identifying additional factors that may influence alertness at any given point in time. Our results indicate that, at least for the range of sleep durations and wake-up times commonly found on rotating shift systems, we may assume the phase of the endogenous circadian component of alertness (process C) to be “set” by the time of waking. Such an assumption considerably enhanced the predictive power of the model and yielded remarkably similar phase estimates to those obtained by maximizing the post-hoc fit of the model. We then examined the manner in which obtained ratings differed from predicted values over a complete 8-day cycle of two, 12-h shift systems. This revealed a pronounced “first night compensation effect” that resulted in shift workers rating themselves as progressively more alert than would be predicted over the course of the first night shift. However, this appeared to be achieved only at the cost of lowered ratings on the second night shift. Finally, we were able to identify a “time on shift” effect whereby, with the exception of the first night shift, alertness ratings decreased over the course of each shift before showing a modest “end effect.” We conclude that the identification of these additional components offers the possibility that in the future we may be able to predict trends in accident risk on abnormal sleep-wake schedules.

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.

Comparison of eight and 12 hour shifts: impacts on health, wellbeing, and alertness during the shift.

OBJECTIVES: The generally agreed view is that there is no ideal shift system, and that most systems will have both advantages and disadvantages. As such, attention has been placed on trying to identify good and bad features of shift systems, with a view to minimising the possible ill health as a consequence of shiftwork. The present study focuses on the duration of the shift and looks at the implications for individual health, wellbeing, and alertness during the shift of extending the shift from the traditional eight hours to 12. METHODS: Two groups of chemical workers, one working 12 hour shifts and the other working eight hour shifts, took part. All completed a modified version of the standard shiftwork index (SSI), a set of self reported questionnaires related to health and wellbeing. RESULTS: The two groups did not differ on most outcome measures, although the differences that did exist suggested advantages for the 12 hour shift workers over the eight hour shift workers; with the notable exception of rated alertness at certain times of day. CONCLUSIONS: The results are explained in terms of the design of the 12 hour shift system and the specific sequencing of shifts that seem to minimise the potential for the build up of fatigue. Although the current data moderately favour 12 hour shifts, a cautionary note is sounded with regard to the implications of the alertness ratings for performance and safety.

Chronic effects of shift work on cognition: findings from the VISAT longitudinal study

Objectives Shift work, like chronic jet lag, is known to disrupt workers’ normal circadian rhythms and social life, and to be associated with increased health problems (eg, ulcers, cardiovascular disease, metabolic syndrome, breast cancer, reproductive difficulties) and with acute effects on safety and productivity. However, very little is known about the long-term consequences of shift work on cognitive abilities. The aim of this study was to assess the chronicity and reversibility of the effects of shift work on cognition. Methods We conducted a prospective cohort study of 3232 employed and retired workers (participation rate: 76%) who were 32, 42, 52 and 62 years old at the time of the first measurement (t1, 1996), and who were seen again 5 (t2) and 10 (t3) years later. 1484 of them had shift work experience at baseline (current or past) and 1635 had not. The main outcome measures were tests of speed and memory, assessed at all three measurement times. Results Shift work was associated with impaired cognition. The association was stronger for exposure durations exceeding 10 years (dose effect; cognitive loss equivalent to 6.5 years of age-related decline in the current cohort). The recovery of cognitive functioning after having left shift work took at least 5 years (reversibility). Conclusions Shift work chronically impairs cognition, with potentially important safety consequences not only for the individuals concerned, but also for society.

Effects of direction of rotation in continuous and discontinuous 8 hour shift systems

OBJECTIVES Previous research has produced conflicting evidence on the relative merits of advancing and delaying shift systems. The current study assessed the effects of the direction of shift rotation within 8 hour systems, upon a range of measures including sleep, on shift alertness, physical health, and psychological wellbeing. METHODS An abridged version of the standard shiftwork index which included retrospective alertness ratings was completed by four groups of industrial shiftworkers on relatively rapidly rotating 8 hour systems (n=611). Two groups worked continuous systems that were either advancing or delaying; the other two groups worked discontinuous systems that were either advancing or delaying. RESULTS Few effects were found of direction of rotation on chronic measures of health and wellbeing, even when the systems incorporated “quick returns” (a break of only 8 hours when changing from one shift to another). This was despite the use of measures previously shown to be sensitive to the effects of a broad range of features of shift systems. However, advancing continuous systems seemed to be associated with marginally steeper declines in alertness across the shift (F (3,1080)=2.87, p<0.05). They were also associated with shorter sleeps between morning shifts (F (1,404)=4.01, p<0.05), but longer sleeps between afternoons (F (1,424)=4.16, p<0.05). CONCLUSIONS The absence of negative effects of advancing shifts upon the chronic outcome measures accorded with previous evidence that advancing shifts may not be as harmful as early research indicated. However, this interpretation is tempered by the possibility that difficult shift systems self select those workers most able to cope with their deleterious effects. The presence of quick returns in advancing continuous systems seemed to impact upon some of the acute measures such as duration of sleep, although the associated effects on alertness seemed to be marginal.

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.

Review of studies that have used the Standard Shiftwork Index: Evidence for the underlying model of shiftwork and health

The Standard Shiftwork Index (SSI) provides shiftwork researchers with a standardised battery for assessing the impact of shiftwork on psychological and physiological well-being. We review the published SSI literature and evaluate the extent to which the results of these publications support the model underpinning the SSI. A total of 70 SSI publications were identified, of which 41 were selected. The 41 studies were published between 1993 and 2006 and had a combined total of 21,420 respondents. The analysis indicated support for parts of the SSI model, particularly in relation to the impact of shift systems design on individual well-being, as well as the role of individual factors (e.g., personality, coping style). However, evidential support for the model as a whole is incomplete. The findings of the reviewed studies are summarised and methodological limitations are discussed.

The impact of free-time activities on sleep, recovery and well-being.

We compared the effects of different types of free-time activity on subjective and objective indices of sleep, recovery and well-being in an experimental field study. Twelve participants spent four consecutive evenings after work in each of three conditions: pursuing quiet leisure activities at home; undertaking active leisure pursuits; doing additional work. Ratings of rest and recuperation, and of satisfaction, were lowest in the additional work condition. There were few other differences between conditions. However, being satisfied with ones evening activities (regardless of which experimental condition was being undertaken) was associated with improved subsequent sleep (self-reported). Evening activities involving lower mental effort were also associated with better-rated sleep, as well as improved recuperation and fatigue the next day. It is concluded that the nature of activity per se may be less important than (1) whether the activity accords with individual preference and (2) the cumulative demands of daytime and evening activities.