Abstract: We investigated the association between worktime control and fatigue, sleep problems, and depressive symptoms in a sample of daytime and shift workers. A total of 3681 permanent daytime workers and 599 shift workers completed a questionnaire designed to assess the above variables. Worktime control was evaluated in terms of both "control over daily working hours" and "control over days off". Worktime control × work schedule × gender analysis of covariance, adjusted for age and employment status, showed overall reductions in incomplete recovery, insomnia symptoms, daytime sleepiness, and depressive symptoms with increasing levels of worktime control. However, no associations between control over daily working hours and insomnia symptoms were observed in women. The reductions appeared to be more evident for control over days off. These results remained consistent after adjustments for other potential covariates. The present findings indicate that increased worktime control and enhanced control over days off in particular, may be associated with favorable health outcomes.
Abstract: OBJECTIVES: This study was conducted to determine whether extended sleep time during the weekend improves alertness and performance during the subsequent week for workers who are habitually short on sleep time. METHODS: Daytime employees in the manufacturing industry [38.3, standard deviation (SD) 8.1 years old, mean weekday sleep ≤6 hours] participated in a study that lasted 3 successive weeks. Participants were instructed to stay in bed for ≥8 hours between 22:00-09:00 hours on weekends during the first week as a sleep intervention condition and keep their habitual sleep-wake patterns as a habitual weekend sleep condition beginning the weekend of the second week through Thursday of the third week. Half the participants underwent the conditions in one order and the other half in the reverse. Sleep was monitored by an actigraph. A psychomotor vigilance task, subjective fatigue, and blood pressure were measured on Monday and Thursday during the afternoon each week. RESULTS: Sleep duration on weekends was approximately 2 hours longer per day during the intervention. However, sleep duration during weekdays following the intervention returned to shorter periods. Significantly shorter reaction times and a smaller number of lapses on the psychomotor vigilance task were found on Mondays after the intervention than after the habitual weekend sleep. The opposite results, however, were observed on Thursdays. CONCLUSIONS: Sleep extension on weekends may be effective in improving alertness and performance during the first days in subsequent weeks among workers with short sleep times. These benefits might be maintained if sufficient sleep duration continues.
Abstract: Napping is one strategy that may assist night shiftworkers to cope with sleepiness and fatigue. However, one potential disadvantage of napping is that awakening from naps is disturbed by sleep inertia, which has also been found to impair performance and/or mood, transiently. The authors examined the effects of the timing and length of a night-shift nap on sleep inertia in a laboratory setting. Twelve male university students (mean +/- SD: 21.6 +/- 2.8 yrs) participated in this 3-day experiment, during which included a simulated night shift (22:00-08:00 h) and subsequent day (11:30-17:30 h) and night sleep (00:00-07:00 h). The simulated night shift was designed to include one of five (four nap/one no-nap) conditions. The napping conditions differed by their timing and duration: 00:00-01:00 h (Early 60 min; E60), 00:00-02:00 h (Early 120 min; E120), 04:00-05:00 h (Late 60 min; L60), 04:00-06:00 h (Late 120 min; L120). Participants completed all the experimental conditions in a counterbalanced order. Rectal temperature (R(T)) was recorded throughout the simulated shift and polysomnography (PSG) was recorded during the nap period. Immediately before and after each nap, participants were required to complete a visual analogue scale (VAS) to assess sleepiness and a visual vigilance test (VVT). During the simulated night shift, a set of tasks (an English transcription task, a performance test battery, and a break) was repeated hourly, except during the periods of napping. For each nap condition, the VAS and VVT (reaction time [RT]; lapses >5 s) results were analyzed by two-way, repeated-measures analysis of variance (ANOVA) (nap [nap versus no-nap] x time point [pre-nap versus post-nap]). PSG and R(T) data were analyzed with one-way repeated-measures ANOVA. Marginally significant interactions were observed for RTs and lapses in VVT for the L60 nap condition (p = .071 and p = .070, respectively). However, those effect sizes were moderate (partial eta(2) = 0.266, 0.268, respectively). Post hoc analyses showed significantly longer RTs (p < .05) and more lapses (p < .05) following the L60 nap compared with no nap. In contrast, there was no significant difference in sleepiness between the L60, or any of the other nap conditions, and the no-nap condition. Our findings suggest the effect of sleep inertia on VVT performance was profound in the L60 condition, although no significant effects on sleepiness were self-reported by VAS. The dissociation between performance and sleepiness might reflect an unstable state where participants cannot perceive decline in their performance. The present findings are significant in terms of occupational safety; the practical implication is that great care is needed when taking a 1-h nap between 04:00 and 05:00 h on the night shift.
Abstract: The aims of the study were to investigate the systematic classification of subsidiary behaviors during visual display terminal (VDT) work and discuss the interpretation of these behaviors through an interactive model of subsidiary behaviors, work performance and autonomic nerve activity.
Abstract: Increased night work is an important issue because of its implications on workers' health, safety and performance. This study examined the effects of brief hourly exercise as a countermeasure against the adverse effects of night work, especially for workers requiring sustained attention while working in a prolonged sitting posture. During simulated night work (22:00-08:00), participants were required to follow an hourly schedule comprising a 30-min task, 15-min test and 15-min break. The study included 2 experimental conditions: (1) hourly exercise (HE; hourly exercise for 3 min during breaks) and (2) control (without exercise during breaks). Throughout the test period, work performance in the last 10 min of each 30-min task was better under the HE condition than under the control condition (p<0.01). During the second half of the test period, exercise showed an effect on sustained attention (p=0.02). Parasympathetic nerve activity under the HE condition was less than that under the control condition (p<0.01). However, exercise was not effective in reducing subjective fatigue and sleepiness. These results suggest that brief hourly exercise acts as a restraint on parasympathetic nerve activity and is capable of sustaining attention levels during the circadian rhythm nadir that occurs during early morning.
Abstract: The purpose of this study was to characterize the recovery pattern of sleep following simulated, four successive night shifts in ten healthy men (22.9 + or - 3.2 yr). Poor sleep was defined as sleep efficiency of 80% or lower as determined actigraphically. The results showed that four (rapid, slow, pseudo, and incomplete) patterns of sleep recovery were observed over three recovery sleep periods. The rapid and slow recovery pattern represented immediate and slow return to baseline level prior to the nightshifts, respectively. The pseudo recovery pattern demonstrated poor sleep at the 3rd recovery sleep period, despite transient recovery at the 2nd sleep period. The incomplete recovery pattern was characterized by consistently poorer sleep during the entire recovery period. The correlation analysis indicated that sleep habits (bed time and variation of wake time) prior to the experiment were significantly related to the recovery patterns, rather than performance and alertness during the night shifts.
Abstract: The aim of the present study was to reveal characteristic patterns of fatigue feelings on consecutive night shifts by a questionnaire for work-related fatigue feelings "Jikaku-sho shirabe". Ten healthy males (Mean +/- SD: 22.9 +/- 3.2 years old) participated in the experiment. Participants were required to attend the laboratory for nine consecutive nights under the following conditions: adaptation sleep (0:00-7:00), simulated day shift (10:00-18:00), baseline sleep (0:00-7:00), directly followed by four simulated night shifts (22:00-9:00) and the subsequent daytime sleep (12:00-18:00), three recovery nights (0:00-7:00) and two simulated day shifts (10:00-18:00). During each simulated shift, participants were required to complete an English transcription task (30 min), a performance test battery (20 min) and break (10 min) every hour. Fatigue feelings were evaluated by "Jikaku-sho shirabe", which was proposed by the Industrial Fatigue Research Committee of the Japan Occupational Health in 2002. This questionnaire consists of 25 subjective fatigue symptom items that are categorized into 5 factors: feeling of drowsiness (Factor I), feeling of instability (Factor II), feeling of uneasiness (Factor III), feeling of local pain or dullness (Factor IV), and feeling of eyestrain (Factor V). For each item, respondents are requested to estimate the intensity of the feelings as "Disagree at all," "Agree scarcely," "Agree slightly," "Agree considerably," and "Agree strongly." These five intensities were assigned scores of 1 to 5 points, respectively. Hierarchical cluster analysis suggested that there might be at least three variation patterns of fatigue feelings on the consecutive night shifts (i.e. Clusters A, B and C). On the basis of subjective fatigue symptom items of each cluster, the patterns in Clusters A, B and C might reflect the loads of the reticular activating system, musculoskeletal and central nervous systems, and limbic system, respectively. For Clusters A and C, significant improvements were observed with the increase of the number of night shifts (F(11,99)=3.07, p<0.01, F(11,99)=3.37, p<0.01, respectively). On the other hand, Cluster B deteriorated with the progress of the simulated night shifts. Taken together, we suggest that the characteristic patterns of fatigue feelings on consecutive night shifts might represent dissociation among the feelings induced by several loads.
Abstract: Adjustable sit-stand workstations, which are designed to allow workers to sit and stand autonomously while working, were examined to identify the effects on workers' musculoskeletal discomfort, alertness and performance. Twenty-four healthy subjects participated in the study. The subjects were required to do an English transcription task for 150 min under the following conditions: 1) sitting at standard workstations (Standard), 2) sitting on a chair with the work surface elevated to standing position (High-chair) and 3) a combination of 10-min sitting and 5-min standing with the same setting as that in the high-chair condition (Sit-stand). The subjective musculoskeletal discomfort scores indicated that High-chair and Sit-stand resulted in relatively higher discomfort levels than the Standard condition. Although the ratio between low-frequency (0.04-0.15 Hz) and high-frequency (0.15-0.4 Hz) components of heart rate variability (LF/HF ratio) in Sit-stand was higher than that in other conditions, there were no significant differences in subjective sleepiness among the three conditions. As for work performance, there was a tendency to be steadily high under the Sit-stand condition compared with other conditions, but not a significant difference. This study revealed that although the use of sit-stand workstations can contribute to keeping workers' arousal level steady, it has an adverse effect in light of musculoskeletal discomfort.
Abstract: The study examined how nap length, nap timing and sleep quality affect early morning performance (6:00 to 8:00). Twelve students participated in a simulated nightshift schedule (22:00 to 8:00) where the length and timing of nocturnal naps were manipulated (0:00-1:00, 0:00-2:00, 4:00-5:00 and 4:00-6:00). A performance test battery was administered consisting of a psychomotor vigilance test, a logical reasoning test, and a visual analogue scale for subjective fatigue and sleepiness. The results showed that a 120-min nap sustained early morning performance better than a 60-min nap. Taking a nap earlier or later did not affect the neurobehavioral performance tests, although participants slept more efficiently during naps later in the night shift. A negative effect of a nocturnal nap during the night shift on subsequent daytime and nocturnal sleep was not observed in the sleep architecture. It still remains unclear whether slow wave sleep plays an important role in sustaining early morning performance. In terms of work safety and sleep health, the results suggest that a longer and later nap is beneficial during night shifts.
Abstract: This study examined the effects of a health education program based on the self- reliance and self-action philosophy and the use of group work methodology on hypercholesterolemia during and after the intervention period. Thirty-two people participated in the study. Measurement values were obtained at the commencement of the intervention (Baseline), during the 6-month intervention period, at the end of the 6-month intervention period (Middle Point) and 6 months after Middle Point (End Point). The average number of steps per day significantly increased during the 6-month intervention period. The energy intake and fat intake levels significantly decreased during the 6-month intervention period. Total cholesterol, triglyceride, and atherosclerosis-index levels significantly decreased between Baseline and End Point. The HDL cholesterol levels significantly increased between Baseline and End Point. Statistically significant decrease was also observed in total cholesterol and atherosclerosis-index levels between Baseline and Middle Point, and between Middle Point and End Point. It is concluded that the health education program based on self-reliance and self-action philosophy using a group work methodology is effective for improving hypercholesterolemia. Especially, the improvement in the serum total cholesterol and atherosclerosis-index levels was sustained even after the intervention period.
Abstract: Nighttime napping is an effective measure to prevent adverse effects due to night shift work. A characteristic of nighttime nap is that it can result in considerably deeper sleep. Several studies have shown that taking nighttime naps suppressed increasing sleepiness, decreasing alertness during the period following awaking from a nap, and prevented disturbance of circadian rhythm ("anchor sleep"). The length of daytime sleep after night shift, when combined with a nighttime nap, is shorter than that without nap. This finding might be interpreted as a beneficial effect rather than a negative feature because workers can then spend time engaged in other activities rather than sleeping. Nevertheless, the introduction of nighttime sleep break in the workplace has not been widely accepted. To promote nighttime napping strategy in the workplace, consensus building while acting on conflicting interest is essential. Recently, participatory method for improvement of working condition has expanded worldwide. A characteristic of the activity is using action checklist and group work, and heightening motivation to improvement working condition between worker and manager. Through the activities, nighttime napping strategy would be spread more in the workplaces and play a role as one of the effective tools for improving working conditions, work performance and safety in the future.
Abstract: To examine the effects of the length and timing of nighttime naps on performance and physiological functions, an experimental study was carried out under simulated night shift schedules.
