Biomedical subjects

S Folkard

Publications and source records attributed to S Folkard.

At least 37 records · Page 2Linked to original sources

PubMed1998

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.

Humans↗

PubMed1998

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.

Adaptation, Psychological↗

PubMed1998

Time of day effects in, and the relationship between, sleep quality and movement.

The study aimed to measure the effects of a 27-h 'day' sleep-wake regime on actigraphic and subjective sleep variables, and to examine the relationships between these variables. Nine subjects spent 30 days and nights in the laboratory. After sleeping 8 h for each of 8 nights, the subjects had an imposed 27-h 'day', for 18 'days', remaining in bed for 9 h on each sleep period. Sleep periods therefore started 3 h later each day, although subjects' circadian rhythms stayed entrained to 24 h, because subjects were not isolated from the natural light-dark cycle. Time asleep, subjective sleep efficiency and subjective sleep quality, but not movement during sleep, were found to be significantly affected by time of going to bed. There were significant decreases in movement during recovery sleeps following each of two episodes of 26 h sleep deprivation. Over the study there were significant within-subject correlations between subjective sleep quality and subjective sleep efficiency (rav = 0.65), movement during sleep and subjective sleep efficiency (rav = -0.48), and movement during sleep and subjective sleep quality (rav = -0.26). We conclude that sleep movement, despite its low within- and between-subjects variability, is nevertheless a statistically reliable, but weak, indicator of subjective sleep efficiency and quality.

Adult↗

PubMed1998

Work shift duration: a review comparing eight hour and 12 hour shift systems.

OBJECTIVES: Shiftwork is now a major feature of working life across a broad range of industries. The features of the shift systems operated can impact on the wellbeing, performance, and sleep of shiftworkers. This paper reviews the current state of knowledge on one major characteristic of shift rotas-namely, shift duration. Evidence comparing the relative effects of eight hour and 12 hour shifts on fatigue and job performance, safety, sleep, and physical and psychological health are considered. At the organisational level, factors such as the mode of system implementation, attitudes towards shift rotas, sickness absence and turnover, overtime, and moonlighting are discussed. METHODS: Manual and electronic searches of the shiftwork research literature were conducted to obtain information on comparisons between eight hour and 12 hour shifts. RESULTS: The research findings are largely equivocal. The bulk of the evidence suggests few differences between eight and 12 hour shifts in the way they affect people. There may even be advantages to 12 hour shifts in terms of lower stress levels, better physical and psychological wellbeing, improved durations and quality of off duty sleep as well as improvements in family relations. On the negative side, the main concerns are fatigue and safety. It is noted that a 12 hour shift does not equate with being active for only 12 hours. CONCLUSIONS: There can be considerable extension of the person's time awake either side of the shift. However, the effects of longer term exposure to extended work days have been relatively uncharted in any systematic way. Longitudinal comparative research into the chronic impact of the compressed working week is needed.

Absenteeism↗

PubMed1998

Effects of the endogenous clock and sleep time on melatonin, insulin, glucose and lipid metabolism.

This study was undertaken to determine whether the internal clock contributes to the hormone and metabolic responses following food, in an experiment designed to dissociate internal clock effects from other factors. Nine female subjects participated. They lived indoors for 31 days with normal time cues, including the natural light: darkness cycle. For 7 days they retired to bed from 0000 h to 0800 h. They then underwent a 26-h 'constant routine' (CR) starting at 0800 h, being seated awake in dim light with hourly 88 Kcal drinks. They then lived on an imposed 27-h day (18 h of wakefulness, 9 h allowed for sleep), for a total of 27 days. A second 26-h CR, starting at 2200 h, was completed. During each CR salivary melatonin and plasma glucose, triacylglycerol (TAG), non-essential fatty acids (NEFA), insulin, gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) were measured hourly. Melatonin and body temperature data indicated no shift in the endogenous clock during the 27-h imposed schedule. Postprandial NEFA, GIP and GLP-1 showed no consistent effects. Glucose, TAG and insulin increased during the night in the first CR. There was a significant effect of both the endogenous clock and sleep for glucose and TAG, but not for insulin. These findings may be relevant to the known increased risk of cardiovascular disease amongst shift workers.

Adult↗

PubMed1998

Shift length as a determinant of retrospective on-shift alertness.

OBJECTIVES: This study examined the combined effects of shift length (8 versus 12 hours) and night-to-morning-shift changeover time (0600 versus 0700) on retrospective on-shift alertness ratings. METHODS: An abridged version of the Standard Shiftwork Index, which included retrospective alertness ratings, was completed by 4 groups of industrial shift workers. Two groups worked 8-hour shift systems and started their morning shifts at either 0600 or 0700; the other 2 groups worked 12-hour systems, starting their day shifts at either 0600 or 0700. RESULTS: The 8-hour workers reported considerably higher levels of alertness in the afternoon, while the 12-hour workers were more alert than the 8-hour workers in the morning and at 2200. Workers who started their shift around 0600 were less alert during the morning than those who started around 0700. The data suggested that the combined effects of working 8-hour shifts and starting the morning shift at around 0600 have particularly deleterious effects upon alertness. CONCLUSIONS: Effects on alertness can be explained in terms of differences in elapsed time on duty, sleep duration, sleep disruption, and chronic fatigue. The findings of this study appear to contradict previous research demonstrating that the major deleterious effects of extended shifts and delayed changeovers upon alertness occur at night. However, it is acknowledged that the absence of a difference in alertness at night may have been due to floor effects. Nevertheless, the implications of the alertness ratings for performance and safety, particularly during the afternoon, should not be ignored.

Adult↗

PubMed1998

Diurnal trends in mood and performance do not all parallel alertness.

OBJECTIVES: This study examined the hypothesis that alertness can be used to predict time-of-day effects on performance. METHODS: For 6 or 7 days the volunteers (24, highly practiced young women) were required to retire to bed at 0000 and were awakened at 0800. A battery of mood and performance tests was completed every 2 hours while the women were awake; the result was 9 equally spaced measures per day. Measures of mood, serial reaction time, and memory scanning were recorded. Rectal temperature was recorded continuously. RESULTS: After omitting the data from the first day to avoid any carry-over from the "first-night" effect on sleep, average time-of-day functions were calculated for each subject, for each variable, and were then z-transformed. Cross-correlations between the pooled time-of-day trends indicated that, while alertness was a reasonably good "predictor" of the simple perceptual-motor speed measures, it fared less well for some of the other measures. Two-way analyses of variance indicated that the time-of-day trend for all measures differed from that for alertness, although the magnitude of this difference varied substantially and, for some measures, was very largely due to the last reading of the day (0000). CONCLUSION: It is clear from these results that, while alertness may successfully "predict" variations in some measures of performance capability, and especially those of simple perceptual motor speed, care should be exercised in extrapolating to other performance measures.

Adolescent↗

PubMed1997

Complex interaction of the sleep-wake cycle and circadian phase modulates mood in healthy subjects.

BACKGROUND: Several studies of healthy volunteers have revealed that subjective mood may vary with the duration of prior wakefulness and with the time of day. However, in these studies, the effects of extended wakefulness and circadian phase remained confounded, and the interaction of these 2 processes could not be assessed quantitatively. METHODS: In the present study, a total of 24 healthy young subjects (16 men, 8 women) lived on a 30-hour sleep-wake schedule for 19 to 23 days or on a 28-hour sleep-wake schedule for 33 to 36 days; both schedules induced desynchrony between the subjects' sleep-wake cycle and their endogenous circadian pacemaker. Subjective mood was assessed by 2 types of visual analog scales, which were administered twice every 2 hours and every 20 minutes, respectively, during all scheduled wakefulness episodes. A circadian phase and an interval elapsed since awakening were attributed to each data point, and circadian and wake-dependent fluctuations of mood were assessed. RESULTS: A significant variation of mood with circadian phase was observed, but no reliable main effect of the duration of prior wakefulness was found. A statistically significant interaction of circadian and wake-dependent fluctuations was evident; when the analysis was restricted to specific circadian phases, mood improved, deteriorated, or remained stable with the duration of prior wakefulness. CONCLUSIONS: These results indicate that, in healthy young subjects, subjective mood is influenced by a complex and nonadditive interaction of circadian phase and duration of prior wakefulness. The nature of this interaction is such that moderate changes in the timing of the sleep-wake cycle may have profound effects on subsequent mood.

Adolescent↗

PubMed1997

Black times: temporal determinants of transport safety.

This paper is concerned with whether transport accident risk tends to peak at particular times, in relation to both time of day and time on task, and with the underlying causes of such peaks. Macro-analyses confirmed the presence of a clear circadian (ca 24 hour) rhythm in road accident risk with a major peak at ca 03:00 but suggested that this rhythm could not be entirely accounted for in terms of drivers falling asleep at the wheel. Sleep propensity clearly shows a pronounced circadian rhythm and performance efficiency in wakeful subjects shows a similar trend implying that the 03:00 road accident peak may simply reflect lowered performance capabilities. However, there are 'residual' peaks in accidents at certain times of day that are difficult to account for in terms of circadian rhythmicity. It is suggested that these may reflect a time on task effect which shows a pronounced, but transient, 2-4 hour peak in risk. Only when individuals had been on duty for 12 hours or more did the risk exceed that found during the 2-4 hour peak. While an explanation for this transient peak is offered, the underlying reason for it is, as yet, uncertain and clearly warrants investigation in view of its practical implications. It is concluded that there are 'black times' when accidents are far more likely and that there is a strong need to investigate possible countermeasures.

Accidents, Occupational↗

PubMed1997

Models of shiftwork and health: an examination of the influence of stress on shiftwork theory.

This paper critically reviews models of shiftwork and health and provides a historical overview of changes in the conceptualization of the association between them. Models are hypothetical and conceptually broad, becoming more so as they move away from linear, chronobiological to multidirectional, psychological conceptualizations. We attribute this tendency to the use of stress frameworks to explain the relationship between shiftwork and health. We assess the usefulness of stress as an explanatory concept in terms of how it affects shiftwork research and practice and make recommendations for future practice and theory development.

Adaptation, Physiological↗

PubMed1997

The three-process model of alertness and its extension to performance, sleep latency, and sleep length.

This paper summarizes a mathematical/computer model for predicting alterness/performance in daily living. The model uses sleep data as input and contains a circadian and a homeostatic component (amount of prior wake and amount of prior sleep), which are summed to yield predicted alertness (on a scale between 1 and 16) as well as performance on monotonous tasks. The model includes an identification of levels at which the risk of performance/ alertness impairment starts, as well as prediction of sleep latency and time of awakening of sleep episodes. It is suggested that the model may be used to evaluate work/rest schedules in terms of sleep-related safety risks.

Circadian Rhythm↗

PubMed1997

Shiftwork Advantages as Predictors of Health.

This study investigated the relationships between shiftwork advantages and subjective health. The Standard Shiftwork Index and a measure of shiftwork advantages were completed by 175 shift workers. Four advantage subscales were developed, corresponding to family, social/domestic, work, and time for oneself. Family advantages were negatively associated with psychological distress, cognitive and somatic anxiety, chronic fatigue, and digestive and cardiovascular symptoms (p < 0.05). After family advantages were partialled out, social/domestic advantages were negatively related to psychological distress (p < 0.05). Variety in work on each shift was significantly related to psychological distress and digestive symptoms. After the effects of shift and personality characteristics were accounted for, family advantages predicted a significant amount of the variance of cognitive anxiety (p < 0.05) and chronic fatigue (p < 0.01), and variety in work, family, and social/domestic advantages predicted a significant amount of variance of psychological distress (p < 0.05). The authors conclude that family advantages are related to psychological health, and to a lesser extent physical health, but that other advantages have little relationship to subjective health.

Journal Article↗

PubMed1997

Effects on Accidents of Time into Shift and of Short Breaks between Shifts.

This study aimed to determine whether there was a peak in accidents in the second to fourth hours within a shift and to compare the effect on accidents of the presence or absence of a break of only eight hours between shifts in a shift cycle ("quick returns"). Archival accident records were obtained for a four-year period from two sister works within the same division of a heavy-industrial organization. The works had many similarities but differed in the shift systems used. One had "quick returns," whereas the other did not. Accident frequencies were analyzed across four variables, site, shift, time on shift, and process code (process code identified the process area in which the worker operated). These were analyzed by hierarchical log-linear analysis, using a significance level of 0.05. The results indicated there was a peak in accidents in the second and third hours into a shift, but provided only slight evidence for a detrimental effect of "quick returns."

Journal Article↗

PubMed1996

Maintaining safety and high performance on shiftwork.

This review of the shiftwork area focuses on aspects of safety and productivity. It discusses the situations in which shiftworker performance is critical, the types of problem that can develop and the reasons why shiftworker performance can be impaired. The review ends with a discnssion of the various advantages and disadvantages of several shift rotation systems, and of other possible solutions to the problem.

Accident Prevention↗

PubMed1996

Predicting sleep latency from the three-process model of alertness regulation.

This paper presents a modification of the quantitative "three-process model of alertness regulation" to predict sleep latency in connection with irregular sleep/wake patterns. This model uses a circadian and a homeostatic component (sleep loss) that are summed to yield predicted alertness (on a scale of 1 to 20) across a specified time span. The timing of sleep from two studies of irregular sleep were used as input to the model. The predicted alertness at bedtime was regressed on empirical sleep latency from two studies. The maximum R2 (0.88) was reached for an exponential function, with the model acrophase set to 2048. The predictions were cross validated on another set of sleep latency data from an irregular sleep study and a maximum R2 of 0.65 was obtained. In both studies, the prediction from the model explained more variance that did self-rated alertness at bedtime. Cross validation was also carried out successfully with published data from two studies of shift work. It was concluded that sleep latency on irregular schedules may be predicted with accuracy from knowledge of the prior sleep/wake pattern. This may have practical consequences for rest/activity management.

Adult↗

PubMed1996

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.

Adult↗

PubMed1996

Predicting duration of sleep from the three process model of regulation of alertness.

OBJECTIVES: Irregular working hours severely disturb sleep and wakefulness. This paper presents a modification of the quantitative (computerised) three process model of regulation of alertness to predict duration of sleep in connection with irregular sleep patterns. METHODS: The model uses a circadian "C" (sinusoidal) and homeostatic "S" (exponential) component (the duration of previous periods awake and asleep), which are summed to yield predicted alertness (on a scale of 1-16). It assumes that waking from sleep will occur at a given alertness level (S' + C') when recuperation is complete. Variables of electroencephalographic duration of sleep from two studies of irregular sleep were used to model the S and C variables in a regression approach to maximise prediction. The model performance was cross validated against published field and laboratory data. RESULTS: The model parameters were defined with a high degree of precision R2 = 0.99 and the validation yielded similar values R2 = 0.98-0.95, depending on the acrophase. The paper also describes a simplified graphical version of the computation model seen as a two dimensional duration of sleep nomogram. CONCLUSION: The model seems to predict group means for duration of sleep with high precision and may serve as a tool for evaluating work and rest schedules to reduce risks of sleep disturbances.

Adult↗

PubMed1996

The difference between activity when in bed and out of bed. II. Subjects on 27-hour "days".

Nine healthy subjects have been studied while exposed to the normal alternation of light and dark, but with their sleep and activity pattern adjusted to a 27-h "day" for 17 imposed "days." Rectal temperature showed clearly the competing influences of 27-h and 24-h components, and these were separated by the method of "purification." The method indicated that the endogenous component had a constant amplitude throughout the experiment and remained entrained to solar (24-h) time; by contrast, the exogenous component followed the imposed 27-h "day" and increased rectal temperature in proportion to the amount of subjects' activity. Wrist movement was used to assess activity while in bed (attempting sleep) and out of bed (when naps were forbidden). While these results confirmed adherence of the subjects to the imposed 27-h "days," they also showed that the dichotomy between "out of bed" activity and "in bed" inactivity depended on the phase relationship between endogenous (24h) and exogenous (27h) components. Thus, the dichotomy was highest and was equal to that during control days (with a conventional 24-h life-style) when the two components were in phase and lowest when the solar and imposed day were in antiphase. This was due to changes in activity, both during time spent in bed and out of bed. We confirm that this protocol can produce valuable information about the properties of the circadian system in humans and the value of the process of purification of temperature data. We have established also that the very simple and noninvasive measurement of wrist movement, coupled with its use to calculate dichotomy indices, provides valuable information that both confirms and extends the results obtained from the more conventional (but also more invasive) measurement of rectal temperature.

Bed Rest↗