The impact of night work on psychological well-being

This study tested the efficacy of selected personality, behavioural, and social/organizational variables as predictors of adaptation to night work. Sixty female student nurses were studied during their first IS months of shiftwork. Twenty-two worked on rotating day and afternoon shifts throughout, while the remaining 38 began regular night shifts after six months. Psychological symptoms were measured at baseline (Stage 1), six months (Stage 2) and 15 months (Stage 3). Repeated measures analysis of variance revealed a significant shift group x symptoms interaction (p < 0·05) between Stages 2 and 3. Only the night workers displayed a significant increase (Tukey HSD: p < 0·01) in symptoms between Stages 1 and 3. Multiple regression analysis revealed that neuroticism and perceived work/nonwork conflict predicted symptoms at Stage 2. Night work, social support from supervisors, and morningness were predictors at Stage 3. These results suggest that organisational, behavioural, and physiological factors moderate the impact of night work on psychological well-being, and personality factors do not.     

The after-effects of night work on short-term memory performance

The aim of this study was to assess the after-effects of night work on mental performance. Twenty experienced shift workers were examined in a baseline condition and during recovery after a night shift period. For control purposes eight other workers were studied in a similar baseline condition and during recovery after a non-night shift period. The subjects performed memory search tasks before and after a bicycle ergometer test. Cycling had different effects on mental performance, leaving the speed and accuracy of the reactions unchanged in the baseline and the non-night-recovery condition, while decreasing the mental performance in the night-recovery condition. Also in this condition a higher level mental effort investment was measured. These results suggest an incomplete recovery on the first fully undisturbed day-off (32 h) after a period of night work, manifesting itself in a deterioration of the efficiency of the information processing.     

Adaptation to permanent night work: the number of consecutive work nights and motivated choice

To study the effects of different patterns of days on and days off duty within a permanent night shift schedule, we studied two groups of female permanent night nurses, one (n=42) working‘many’ nights in a row, and the other (n=36) working ‘few’ nights in a row. The groups were matched for several important moderating variables. All nurses were interviewed individually, and they answered several questionnaires. A MANOVA revealed no statistically significant differences in subjective health between the two groups. Nor was any difference found for satisfaction measures. The many-night group however seemed to put more effort into dealing with their schedule; they used more active coping, had a higher cigarette consumption, and engaged more in sport. They also stayed one hour less in bed during the day after the last night shift. It is concluded that neither schedule was a clear threat to subjective health because the acceptance of permanent night work was the result of a motivated choice and because social support was high. The differences between the two schedules were not large enough to suggest that one of them should be favoured over the other.     

The role of experience in night work: Lessons from two ergonomic studies

The purpose of this article is to analyze some connections between experience, health and work, especially in the field of night work. As a result of the baby boom, the proportion of elderly workers is steadily increasing, while at the same time many workers are reaching retirement age and being replaced by younger people. And, in the same time, there is an overall gradual increase in shift work and night work. To our knowledge, worker experience has not been extensively studied in this context. This was our focus in studying work activity in two very different situations, in a hospital and in a steel industry.In these two studies we observed that the experienced workers endeavor to plan ahead, especially at night. They do this to limit fatigue and to avoid emergencies and ensure that work is stress-free and as far as possible under control. But experience not only brings workers to plan ahead, it also enables them to do so, thanks to the resources it confers: gaining familiarity with tasks and acquiring the ability to identify critical situations, gaining knowledge about themselves and awareness of situations that cause difficulty; and gaining a better overview of the collective aspects of their work and of ways to share tasks or obtain assistance.They are able to undertake these strategies thanks to specific skills and capacities they have built along their professional career, which notably leads them to find the best trade-off between several goals, possibly contradictory.Such experience is especially valuable at night, when the worker is tired, and when there are fewer supervisors present. This experience can only be gained, however, if the work environment fosters its acquisition and provides an opportunity to make use of it, especially during the night shift and especially with respect to planning tasks ahead of time.     

The role of naps in alleviating sleepiness during an irregular sleep-wake schedule

Abstract

Four groups of four subjects have been studied in an isolation unit on an irregular schedule of sleep and waking. Sleep periods of 6h duration were taken at irregular times during the 9-day protocol; they were arranged such that the waking periods lasted 6, 12 or 18 h and were also in an irregular sequence. One-hour naps were taken after 6 and 12 h of waking if the next sleep was not due then. Just before either a nap or a full sleep, subjects assessed their sleepiness and, on rising, they assessed how well sleep had been initiated and maintained. A mathematical model was developed which enabled the effects upon sleepiness of circadian rhythmicity, of the length of the waking period since the last full sleep (time-since-sleep), and of the subjective value of the previous full sleep or nap to be independently quantified. Results showed that there was a tendency for sleepiness to increase, in some cases quite markedly, as the irregular schedule proceeded. There were also effects upon sleepiness due to circadian changes and the amount of time since the last full sleep. These two effects were similar in size and larger than the benefits to be derived from a previous nap or full sleep that had been assessed at the time as having been a good one. We conclude that one-hour naps can play a small role in decreasing an individual's sleepiness and suggest possible means by which their subjective value might be increased.     

The effects of strength testing schedules on muscle strength recovery following static work

In order to measure the recovery of muscle strength after static contractions, strength tests must be performed at various times recovery. This is shown to be an invasive procedure, particularly at typically-recommended schedules of one measurement every 30 s or every 60 s, as the measurement interferes with the recovery process. A predictive equation is given to correct recovery data for this invasiveness.     

Low mean level sustained and intermittent grip exertions: Influence of age on fatigue and recovery

The goal of this study was to quantify localised muscle fatigue resulting from low mean levels of exertion in younger (< 40 years) and older (>50 years) adults. Fatigue, elicited in the finger flexor muscles by intermittent (10% mean maximum voluntary contraction (MVC)) and sustained (8% MVC) handgrip exercises, was quantified by a muscle twitch force response before, immediately after and during 3 h following exercise. Despite greater mean loads, recovery time was shorter following intermittent than sustained contractions, which suggests that recovery from fatigue is more sensitive to rest within the work cycle than mean work. The more pronounced effects for younger than older individuals following the sustained exertion indicate that changes in muscle fibre type composition might predispose older individuals to be more resistant to fatigue resulting from sustained contractions of low level. Performing hand exertion tasks requiring low mean force levels contributes to similar long-lasting fatigue effects regardless of gender and age. Intermittent periods of complete rest reduce muscle fatigue. Since fatigue was not perceived during recovery from the tested sustained and intermittent contractions, subjective evaluations may not be a reliable indicator of localised muscle fatigue.     

The effects of fatigue on performance in simulated nursing work

Fatigue is associated with increased rates of medical errors and healthcare worker injuries, yet existing research in this sector has not considered multiple dimensions of fatigue simultaneously. This study evaluated hypothesised causal relationships between mental and physical fatigue and performance. High and low levels of mental and physical fatigue were induced in 16 participants during simulated nursing work tasks in a laboratory setting. Task-induced changes in fatigue dimensions were quantified using both subjective and objective measures, as were changes in performance on physical and mental tasks. Completing the simulated work tasks increased total fatigue, mental fatigue and physical fatigue in all experimental conditions. Higher physical fatigue adversely affected measures of physical and mental performance, whereas higher mental fatigue had a positive effect on one measure of mental performance. Overall, these results suggest causal effects between manipulated levels of mental and physical fatigue and task-induced changes in mental and physical performance.

Statement of Relevance: Nurse fatigue and performance has implications for patient and provider safety. Results from this study demonstrate the importance of a multidimensional view of fatigue in understanding the causal relationships between fatigue and performance. The findings can guide future work aimed at predicting fatigue-related performance decrements and designing interventions.     

The impact of work-related and personal resources on older workers’ fatigue,work enjoyment and retirement intentions over time

Abstract

This study aims to examine the impact of work-related and personal resources on older workers’ retirement intentions by studying the pathways (fatigue and work enjoyment) from resources to retirement intentions, the buffering role of resources for psychological job demands, in a cross-sectional and longitudinal timeframe. Longitudinal results on a subsample of full-time, older workers (n = 1642) from the Maastricht Cohort Study suggest that over four years of follow-up personal resources like personal mastery and perceived health related to less (prolonged) fatigue and more work enjoyment. Personal mastery also related to later retirement intentions. A work-related resource like decision authority related to less prolonged fatigue. (Prolonged) fatigue related to earlier retirement intentions, suggesting that fatigue may be a pathway to early retirement. Finally, little evidence was found for effect modification by resources. This prospective study indicates that work-related and personal resources may be useful for prolonging working careers.

Practitioner Summary: To date, the impact of work-related and personal resources on older workers’ retirement intentions is rarely studied. As this prospective study shows that resources may impact older workers’ (prolonged) fatigue, work enjoyment and retirement intentions, the monitoring and fostering of resources is of importance for prolonging their working careers.     

The effects of different roster schedules on sleep in miners

Shiftwork involving early morning starts and night work can affect both sleep and fatigue. This study aimed to assess the impact of different rostering schedules at an Australian mine site on sleep and subjective sleep quality. Participants worked one of four rosters;

4 × 4 (n = 14) 4D4O4N4O

7 × 4 (n = 10) 7D4O7N40

10 × 5 (n = 17) 5D5N50

14 × 7 (n = 12) 7D7N70

Sleep (wrist actigraphy and sleep diaries) was monitored for a full roster cycle including days off. Total sleep time (TST) was longer on days off (7.0 ± 1.9) compared to sleep when on day (6.0 ± 1.0) and nightshifts (6.2 ± 1.6). Despite an increase in TST on days off, this may be insufficient to recover from the severe sleep restriction occurring during work times. Restricted sleep and quick shift-change periods may lead to long-term sleep loss and associated fatigue.     

The effects of a self-selected nap opportunity on the psychophysiological,performance and subjective measures during a simulated industrial night shift regimen

This study compared the effects of a 1 h self-selected recovery period to those of a standard night shift arrangement (with a total break time of 1-h) over a simulated three-day night shift schedule in a laboratory setting. Results showed that the inclusion of the flexible nap scheme resulted in higher performance output, improvements in physiological strain responses and reduced sleepiness during each night shift and generally over the three-night cycle. Certain variables also revealed the impact of napping compared with the standard rest break condition on the circadian rhythm. The sleep diary records show that the inclusion of the current intervention did not significantly reduce daytime recovery sleep. The results suggest that the potential benefits of flexible napping may outweigh the logistical effort it requires in a workplace environment.

Practitioner summary: Consensus on appropriate napping strategies for shift work remains a challenge. This simulated night shift laboratory study sought to determine the effects of a 1-h self-selected nap opportunity relative to a normal shift set-up. The nap improved performance and decreased sleepiness, without affecting daytime sleep.     

Impact of SCBA size and fatigue from different firefighting work cycles on firefighter gait

Risk of slips, trips and falls in firefighters maybe influenced by the firefighter’s equipment and duration of firefighting. This study examined the impact of a four self-contained breathing apparatus (SCBA) three SCBA of increasing size and a prototype design and three work cycles one bout (1B), two bouts with a five-minute break (2B) and two bouts back-to-back (BB) on gait in 30 firefighters. Five gait parameters (double support time, single support time, stride length, step width and stride velocity) were examined pre- and post-firefighting activity. The two largest SCBA resulted in longer double support times relative to the smallest SCBA. Multiple bouts of firefighting activity resulted in increased single and double support time and decreased stride length, step width and stride velocity. These results suggest that with larger SCBA or longer durations of activity, firefighters may adopt more conservative gait patterns to minimise fall risk.

Practitioner Summary: The effects of four self-contained breathing apparatus (SCBA) and three work cycles on five gait parameters were examined pre- and post-firefighting activity. Both SCBA size and work cycle affected gait. The two largest SCBA resulted in longer double support times. Multiple bouts of activity resulted in more conservative gait patterns.     

The influence of task design on upper limb muscles fatigue during low-load repetitive work: A systematic review

Ergonomic interventions such as increased scheduled breaks or job rotation have been proposed to reduce upper limb muscle fatigue in repetitive low-load work. This review was performed to summarize and analyze the studies investigating the effect of job rotation and work-rest schemes, as well as, work pace, cycle time and duty cycle, on upper limb muscle fatigue. The effects of these work organization factors on subjective fatigue or discomfort were also analyzed. This review was based on relevant articles published in PubMed, Scopus and Web of Science. The studies included in this review were performed in humans and assessed muscle fatigue in upper limbs. 14 articles were included in the systematic review. Few studies were performed in a real work environment and the most common methods used to assess muscle fatigue were surface electromyography (EMG). No consistent results were found related to the effects of job rotation on muscle activity and subjective measurements of fatigue. Rest breaks had some positive effects, particularly in perceived discomfort. The increase in work pace reveals a higher muscular load in specific muscles. The duration of experiments and characteristics of participants appear to be the factors that most have influenced the results. Future research should be focused on the improvement of the experimental protocols and instrumentation, in order to the outcomes represent adequately the actual working conditions.Relevance to industryIntroducing more physical workload variation in low-load repetitive work is considered an effective ergonomic intervention against muscle fatigue and musculoskeletal disorders in industry. Results will be useful to identify the need of future research, which will eventually lead to the adoption of best industrial work practices according to the workers capabilities.     

The effect of lutein supplementation on visual fatigue: A psychophysiological analysis

We used psychophysiological technology to examine the effect of an oral supplement, a combination of lutein, zeaxanthin and blackcurrant extract (LUT), on visual fatigue, within the context of a randomized, double-blind, placebo-controlled cross-over trial. The LUT supplement and placebo samples were randomly assigned to thirteen participants, who took the samples for two LUT (and vice versa) for another 2 week. Each participant completed visual proof reading tasks for 2 h during each of four testing sessions. Saccade tests were administered before and after the proof reading task, during which the participants moved their eyes back and forth between two targets positioned in the center of two checkerboards. We recorded EEG, EOG, heart rate, and facial muscle potential/performance during the saccade tests. Blood pressure was measured and subjective fatigue and stress scores were collected before and after the proof reading task. We averaged EEG starting at saccade offset in order to analyze eye fixation related potentials (EFRP). Our results suggested that the proof reading task induced visual fatigue. An analysis of EFRP and other psychophysiological data revealed significant differences between the LUT and placebo conditions. These results suggest that supplementation with LUT could help to reduce symptoms of visual fatigue.     

The effect of fatigue on trunk muscle activation patterns and spine postures during simulated firefighting tasks

The purpose of this study was to determine the effect of a fatiguing task (3 min intense stair climbing) on the adopted spinal postures and trunk muscular activation patterns during three highly physically demanding simulated firefighting tasks. Following the fatigue protocol, it was observed that individuals adopted significantly greater spinal flexion (16.3° maximum prior to fatigue as compared to 20.1° post fatigue) and displayed reduced abdominal muscle activation as compared to before the fatigue protocol (mean ranging from 16.6% maximum voluntary contraction (MVC) to 30.6% MVC prior to fatigue as compared to ranging from 14.6% MVC to 25.2% MVC post fatigue). The reduced abdominal activation may be due to a reduction in co-contraction during these tasks, which may compromise spinal stability. Reduced co-contraction combined with the increased spinal flexion may increase the risk of sustaining an injury to the low back.     

基于DM642的嵌入式疲劳驾驶监测系统的实现

针对基于DM642的嵌入式疲劳驾驶监测系统，讨论了系统的总体结构，提出了采用可控光源、奇偶差分帧和人眼跟踪的人眼检测方法。在与奇偶帧图像采集同步的内外圈光源的照射下，利用近轴光源的红眼效应，引起图像奇帧暗瞳孔、偶帧亮瞳孔，由奇偶差分帧快速实现人眼检测与跟踪。同时分析眼睛的特征参数，在一定时间内连续统计眼睛的闭合时间，计算眼睛累计闭合持续时间占某特定时间的百分率（PERCLOS）值来判断疲劳程度并报警。该系统疲劳监测准确率较高，可在汽车驾驶中进行实时疲劳驾驶监测。     

The effect of a resistance-training program on muscle strength, physical workload, muscle fatigue and musculoskeletal discomfort: An experiment

The aim of the study was to investigate the effectiveness of a resistance-training program on muscle strength of the back and neck/shoulder muscles, relative physical workload, muscle fatigue and musculoskeletal discomfort during a simulated assembly and lifting task. Twenty-two workers were randomized over an 8-week resistance-training group, and a control group. Isokinetic muscle strength was assessed using the Cybex dynamometer, muscle fatigue was measured using EMG, and perceived discomfort was measured using a 10-point scale. At the follow-up, we found no effect of the resistance-training program on isokinetic muscle strength of the back and shoulder muscles. Furthermore, we did not find any effect on EMG data, nor on musculoskeletal discomfort during the simulated work tasks. However, trained workers performed the lifting tasks for a longer time before reporting considerable discomfort than those in the control group.     

The effects of glove thickness and work load on female hand performance and fatigue during a infrequent high-intensity gripping task

In various workplaces, gloves are commonly employed to protect the hands with the design rationale of 'the thicker the gloves, the better the protection'. Therefore, the present paper investigated the effects of glove thickness on hand performance and fatigue during two infrequent high-intensity gripping tasks, such as 5-s and sustained tasks. The hand performance was evaluated by maximum volitional contraction (MVC) and its associated time needed to reach the MVC (TMVC), and the total force generation (TFG) during the sustained task. The hand fatigue was assessed by MVC degeneration (DeltaMVC), the shift in time needed to reach the MVC (DeltaTMVC), and the maximal endurance time (MET) associated with the sustained task. Ten female subjects took part in the experiment voluntarily. The four-gloved conditions included bare hand, wearing one layer (Cotton-1), wearing two layers of cotton gloves (Cotton-2), and covering the handle with two layers of cotton glove and exerting with the bare hand (Covered-2). The results indicates that wearing gloves decreased the grip MVC, and the thicker the gloves, the less the grip MVC, but the wearing style did not change the MVC (Cotton-2 MVC was indifferent from Covered-2 MVC). As to muscular fatigue, on the other hand, wearing gloves did not affect DeltaMVC, MET, TMVC, or DeltaTMVC. Due to the greater bare-hand MVC and indifferent MET, bare-hand TFG was better than those conditions with gloves. Finally, the load specified here did not alter TMVC or DeltaTMVC, but the greater the load, the more strength degeneration (DeltaMVC) was induced.     

Electromyographical study on surgeons in urology. II. Determination of muscular fatigue

Abstract

An electromyographical fatigue analysis was performed in the operating theatre on four surgeons during 14 urological operations in which ‘direct endoscopy’ (cf. Luttmann el al. 1996, Part I) was applied. Surface electromyograms (EMG) were derived from the m. trapezius on both sides of the body, the right m. deltoideus, and the left m. erector spinae. The surgeons’ activities were documented by simultaneously recording an electrical activity code signal parallel to the EMGs. The electrical activity (EA) was formed from the raw EMG by rectification and continuous averaging. For purposes of spectral analysis, the EMGs were digitized and converted to the frequency domain by Fast Fourier Transformation. During the performance of endoscopic surgery, an increase in EA, as well as a spectral shift towards lower frequencies, are observed for at least one of the muscles under test in all of the operations. This indicates the development of muscular fatigue in the course of the operations. The finding is confirmed by applying a newly developed method for the joint analysis of the spectrum and the amplitude of EMGs (JASA) which permits discrimination between fatigue-induced and force-related changes in the EMG. Utilizing this method, the development of fatigue was confirmed for 11 of the 14 operations in the case of the right m. trapezius. The right trapezius muscle therefore constitutes a bottleneck for the performance of the operations. The endurance time was estimated from the increase in EA and compared with the actual duration of the operations. Since both are of the same order of magnitude, it is concluded that the final part of an operation has to be performed when the muscles are already fatigued. Application of the newly available method known as ‘monitor endoscopy’ (cf. Part I) can lead to a reduction in muscular strain and fatigue. This, in turn, will enable operations to be performed at less risk to the patient.