The effect of sleep restriction, with or without high-intensity interval exercise, on behavioural alertness and mood state in young healthy males.

Mood state and alertness are negatively affected by sleep loss, and can be positively influenced by exercise. However, the potential mitigating effects of exercise on sleep-loss-induced changes in mood state and alertness have not been studied comprehensively. Twenty-four healthy young males were matched into one of three, 5-night sleep interventions: normal sleep (NS; total sleep time (TST) per night = 449 ± 22 min), sleep restriction (SR; TST = 230 ± 5 min), or sleep restriction and exercise (SR + EX; TST = 235 ± 5 min, plus three sessions of high-intensity interval exercise (HIIE)). Mood state was assessed using the profile of mood states (POMS) and a daily well-being questionnaire. Alertness was assessed using psychomotor vigilance testing (PVT). Following the intervention, POMS total mood disturbance scores significantly increased for both the SR and SR + EX groups, and were greater than the NS group (SR vs NS; 31.0 ± 10.7 A.U., [4.4-57.7 A.U.], p = 0.020; SR + EX vs NS; 38.6 ± 14.9 A.U., [11.1-66.1 A.U.], p = 0.004). The PVT reaction times increased in the SR (p = 0.049) and SR + EX groups (p = 0.033) and the daily well-being questionnaire revealed increased levels of fatigue in both groups (SR; p = 0.041, SR + EX; p = 0.026) during the intervention. Despite previously demonstrated physiological benefits of performing three sessions of HIIE during five nights of sleep restriction, the detriments to mood, wellness, and alertness were not mitigated by exercise in this study. Whether alternatively timed exercise sessions or other exercise protocols could promote more positive outcomes on these factors during sleep restriction requires further research.

Managing Travel Fatigue and Jet Lag in Athletes: A Review and Consensus Statement.

Athletes are increasingly required to travel domestically and internationally, often resulting in travel fatigue and jet lag. Despite considerable agreement that travel fatigue and jet lag can be a real and impactful issue for athletes regarding performance and risk of illness and injury, evidence on optimal assessment and management is lacking. Therefore 26 researchers and/or clinicians with knowledge in travel fatigue, jet lag and sleep in the sports setting, formed an expert panel to formalise a review and consensus document. This manuscript includes definitions of terminology commonly used in the field of circadian physiology, outlines basic information on the human circadian system and how it is affected by time-givers, discusses the causes and consequences of travel fatigue and jet lag, and provides consensus on recommendations for managing travel fatigue and jet lag in athletes. The lack of evidence restricts the strength of recommendations that are possible but the consensus group identified the fundamental principles and interventions to consider for both the assessment and management of travel fatigue and jet lag. These are summarised in travel toolboxes including strategies for pre-flight, during flight and post-flight. The consensus group also outlined specific steps to advance theory and practice in these areas.

The effects of hydration on cognitive performance during a simulated wildfire suppression shift in temperate and hot conditions.

The effects on dehydration and cognitive performance from heat and/or physical activity are well established in the laboratory, although have not yet been studied for personnel working in occupations such as wildland firefighting regularly exposed to these types of conditions. This study aimed to investigate the effects of temperature and dehydration on seventy-three volunteer firefighters (35.7 ±â€¯13.7 years, mean ±â€¯standard deviation) during a simulation of wildfire suppression under either control or hot (18-20; or 33-35 °C) temperature conditions. Results showed cognitive performance on the psychomotor vigilance task declined when participants were dehydrated in the heat and Stroop task performance was impaired when dehydrated late in the afternoon. Firefighters may be at risk of deteriorations in simple cognitive functions in the heat whilst dehydrated, although may also experience impairments in complex cognitive functions if dehydrated late in the day, irrespective of the environmental temperature.

Working Time Society consensus statements: Regulatory approaches to reduce risks associated with shift work-a global comparison.

A large number of workers worldwide engage in shift work that can have significant influences upon the quality of working life. For most jurisdictions, setting and enforcing appropriate policies, regulations, and rules around shift work is considered essential to (a) prevent potentially negative consequences of shift work and (b) to improve worker health and well-being. However, the best ways to do this are often highly contested theoretical spaces and often culturally and historically bound. In this paper, we examine the regulatory approaches to regulating shift work in four different regions: Europe, North America, Australasia, and East Asia (Japan, China, and Korea). Despite the fact that social and cultural factors vary considerably across the regions, comparing regulatory frameworks and initiatives in one region can be instructive. Different approaches can minimally provide a contrast to stimulate discussion about custom and practice and, potentially, help us to develop new and innovative models to improve worker well-being and organizational productivity simultaneously. In this paper, our goal is not to develop or even advocate a "perfect" sets of regulations. Rather, it is to compare and contrast the diversity and changing landscape of current regulatory practices and to help organizations and regulators understand the costs and benefits of different approaches. For example, in recent years, many western countries have seen a shift away from prescriptive regulation toward more risk-based approaches. Advocates and critics vary considerably in what drove these changes and the benefit-cost analyses associated with their introduction. By understanding the different ways in which shift work can be regulated, it may be possible to learn from others and to better promote healthier and safer environments for shift-working individuals and workplaces.

Effects of sleep hygiene and artificial bright light interventions on recovery from simulated international air travel.

PURPOSE: Despite the reported detrimental effects of international air travel on physical performance, a paucity of interventions have been scientifically tested and confirmed to benefit travelling athletes. Consequently, the aim of the present study was to examine the effects of sleep hygiene and artificial bright light interventions on physical performance following simulated international travel. METHODS: In a randomized crossover design, 13 physically active males completed 24 h of simulated international travel with (INT) and without (CON) the interventions. The mild hypoxia and cramped conditions typically encountered during commercial air travel were simulated in a normobaric, hypoxic room. Physical performance, subjective jet-lag symptoms and mood states were assessed in the morning and evening on the day prior to and for two days post-travel. Sleep quantity and quality were monitored throughout each trial. RESULTS: Sleep duration was significantly reduced during travel in both trials (P < 0.01), though total sleep duration during and following travel was almost significantly greater (P = 0.06) in INT (17.0 (16.2-17.8) h) compared to CON (15.7 (14.9-16.5) h). Maximal-sprint and countermovement jump (P < 0.05), but not Yo-Yo Intermittent Recovery level 1 test (P > 0.05) performance, were significantly reduced the evening of day 1 and 2 post-travel, with no differences between trials (P > 0.05). Furthermore, vigour was significantly greater (P = 0.04) the morning of day 2 in INT [5.3 (3.9-6.7)] compared to CON [2.8 (1.4-4.2)], and subjective jet-lag symptoms and mood states were significantly worse on day 2 in CON only (P < 0.05). CONCLUSIONS: Whilst reducing travel-induced sleep disruption may attenuate travel fatigue, no improvements in the recovery of physical performance were apparent.

How well do truck drivers sleep in cabin sleeper berths?

The aim of this study was to evaluate the sleep obtained by livestock transport truck drivers while resting in truck sleeper berths during long-haul commercial operations. Operations were carried out in the very remote regions of Australia. The sample comprised of 32 drivers who wore wrist activity monitors and reported bed-times for a two-week period. Drivers had a mean (±standard deviation) age of 35.41 (± 9.78) years and had worked as truck drivers for 13.83 (± 9.11) years. On average, they obtained 6.07 (± 1.18) hours of sleep/24-h period. The majority of sleep occurred at night, but drivers occasionally supplemented their main sleep with a daytime nap. Consistent with operational demands, drivers were most likely to sleep in cabin sleeper berths (n = 394, 77%). Only a small proportion of sleeps were sampled at home (n = 63, 12%) or at truck depots (n = 56, 11%). Mixed-model ANOVA revealed that while earlier bed-times at home yielded more sleep, there were only marginal differences in sleep quality across location. No intrinsic safety concerns associated with the use of sleeper berths were identified across consecutive days of long-haul transport operations.

The validity of temperature-sensitive ingestible capsules for measuring core body temperature in laboratory protocols.

The human core body temperature (CBT) rhythm is tightly coupled to an endogenous circadian pacemaker located in the suprachiasmatic nucleus of the anterior hypothalamus. The standard method for assessing the status of this pacemaker is by continuous sampling of CBT using rectal thermometry. This research sought to validate the use of ingestible, temperature-sensitive capsules to measure CBT as an alternative to rectal thermometry. Participants were 11 young adult males who had volunteered to complete a laboratory protocol that extended across 12 consecutive days. A total of 87 functional capsules were ingested and eliminated by participants during the laboratory internment. Core body temperature samples were collected in 1-min epochs and compared to paired samples collected concurrently via rectal thermistors. Agreement between samples that were collected using ingestible sensors and rectal thermistors was assessed using the gold-standard limits of agreement method. Across all valid paired samples collected during the study (n = 120,126), the mean difference was 0.06°C, whereas the 95% CI (confidence interval) for differences was less than ±0.35°C. Despite the overall acceptable limits of agreement, systematic measurement bias was noted across the initial 5 h of sensor-transit periods and attributed to temperature gradations across the alimentary canal.

Contribution of core body temperature, prior wake time, and sleep stages to cognitive throughput performance during forced desynchrony.

Shiftworkers are often required to sleep at inappropriate phases of their circadian timekeeping system, with implications for the dynamics of ultradian sleep stages. The independent effects of these changes on cognitive throughput performance are not well understood. This is because the effects of sleep on performance are usually confounded with circadian factors that cannot be controlled under normal day/night conditions. The aim of this study was to assess the contribution of prior wake, core body temperature, and sleep stages to cognitive throughput performance under conditions of forced desynchrony (FD). A total of 11 healthy young adult males resided in a sleep laboratory in which day/night zeitgebers were eliminated and ambient room temperature, lighting levels, and behavior were controlled. The protocol included 2 training days, a baseline day, and 7 x 28-h FD periods. Each FD period consisted of an 18.7-h wake period followed by a 9.3-h rest period. Sleep was assessed using standard polysomnography. Core body temperature and physical activity were assessed continuously in 1-min epochs. Cognitive throughput was measured by a 5-min serial addition and subtraction (SAS) task and a 90-s digit symbol substitution (DSS) task. These were administered in test sessions scheduled every 2.5 h across the wake periods of each FD period. On average, sleep periods had a mean (+/- standard deviation) duration of 8.5 (+/-1.2) h in which participants obtained 7.6 (+/-1.4) h of total sleep time. This included 4.2 (+/-1.2) h of stage 1 and stage 2 sleep (S1-S2 sleep), 1.6 (+/-0.6) h of slow-wave sleep (SWS), and 1.8 (+/-0.6) h of rapid eye movement (REM) sleep. A mixed-model analysis with five covariates indicated significant fixed effects on cognitive throughput for circadian phase, prior wake time, and amount of REM sleep. Significant effects for S1-S2 sleep and SWS were not found. The results demonstrate that variations in core body temperature, time awake, and amount of REM sleep are associated with changes in cognitive throughput performance. The absence of significant effect for SWS may be attributable to the truncated range of sleep period durations sampled in this study. However, because the mean and variance for SWS were similar to REM sleep, these results suggest that cognitive throughput may be more sensitive to variations in REM sleep than SWS.

The relationship between subjective and objective sleepiness and performance during a simulated night-shift with a nap countermeasure.

The aim of the present study was to investigate the relationship between perceived and actual sleepiness and performance during a simulated night-shift that included a 30-min night-nap as an on-duty sleepiness countermeasure. Twenty-four healthy young adults (nine males, fifteen females) participated in a repeated measures design comprising two experimental conditions: no night-nap and 30-min night-nap. Both groups were given a 2-h prophylactic afternoon sleep opportunity (1500-1700 h). Measures of subjective sleepiness (Stanford Sleepiness Scale, Karolinska Sleepiness Scale and Visual Analogue Scale), objective sleepiness (sleep latency tests), objective performance (Symbol-Digit Substitution Task) and reaction time (Psychomotor Vigilance Task) were taken before the night-nap (0230 h) and at several intervals post-nap. Time-series correlation analyses indicated that subjective sleepiness was less correlated with objective sleepiness and objective performance when participants were given a 30-min night-nap. However subjective sleepiness and reaction time performance was strongly correlated in both conditions, and there was no significant difference between the nap and no-nap conditions. Consistent with previous research, results of the present study indicate that subjective and objective indicators of sleepiness and performance may not always correspond, and this relationship may be reduced by the inclusion of a night-nap.

Prediction of probabilistic sleep distributions following travel across multiple time zones.

STUDY OBJECTIVES: To parameterize and validate a model to estimate average sleep times for long-haul aviation pilots during layovers following travel across multiple time zones. The model equations were based on a weighted distribution of domicile- and local-time sleepers, and included algorithms to account for sleep loss and circadian re-synchronization. DESIGN: Sleep times were collected from participants under normal commercial operating conditions using diaries and wrist activity monitors. PARTICIPANTS: Participants included a total of 306 long-haul pilots (113 captains, 120 first officers, and 73 second officers). MEASUREMENT AND RESULTS: The model was parameterized based on the average sleep/wake times observed during international flight patterns from Australia to London and Los Angeles (global R2 = 0.72). The parameterized model was validated against the average sleep/wake times observed during flight patterns from Australia to London (r2 = 0.85), Los Angeles (r2 = 0.79), New York (r2 = 0.80), and Johannesburg (r2 = 0.73). Goodness-of-fit was poorer when the parameterized model equations were used to predict the variance across the sleep/wake cycles of individual pilots (R2 = 0.42, 0.35, 0.31, and 0.28 for the validation flight patterns, respectively), in part because of substantial inter-individual variability in sleep timing and duration. CONCLUSIONS: It is possible to estimate average sleep times during layovers in international patterns with a reasonable degree of accuracy. Models of this type could form the basis of a stand-alone application to estimate the likelihood that a given duty schedule provides pilots, on average, with an adequate opportunity to sleep.

Layover sleep prediction for cockpit crews during transmeridian flight patterns.

INTRODUCTION: Current models of fatigue and alertness use a combination of biological (circadian) and homeostatic factors to predict sleep and wake. Such models do not include social factors in their calculations. The aim of our analysis was to compare the relative contributions of social and biological factors in models designed to predict the total sleep time (TST) during layover periods between transmeridian flights. METHOD: The study actigraphically collected sleep information from 86 cockpit crew (mean age 46.7 yr, SD 4.3 yr) during round-trip patterns from Australia to Los Angeles (n=15), Europe (n=42), New York (n=10), and Hong Kong (n=19). Linear regression models were constructed to predict TST using data from airline schedules. This schedule information included layover length, flight duration, the number of night hours at the destination (social hours), the number of night hours in Australian Eastern Standard time (biological hours), and time zone displacement. These models were then validated using independent data. RESULTS: Analysis indicated that the schedule data was highly correlated. Linear regression analyses indicated that social night hours account for more variance than biological night hours (r = 0.8 vs. 0.7). Additionally, the layover length achieved a correlation coefficient of 0.9. These results were strengthened when the model parameters were applied to the cross-validation dataset. DISCUSSION: Social night hours significantly influence sleep during international layovers and may be a better predictor than biological night hours. More research must be carried out to determine the validity of these findings in a larger, randomly collected flight sample.