The alerting effects of caffeine, bright light and face washing after a short daytime nap

Sleep Inertia in Aviation

INTRODUCTION: Sleep inertia is the transition state during which alertness and cognitive performance are temporarily impaired after awakening. Magnitude and time course of sleep inertia are characterized by high individual variability with large differences between the cognitive functions affected. This period of impairment is of concern to pilots, who take sleep or nap periods during on-call work hours or in-flight rest, then need to perform safety-critical tasks soon after waking. This review analyzes literature related to sleep inertia and countermeasures applicable for aviation.METHODS: The large part of scientific literature that focuses on sleep inertia is based on studies in patients with chronic sleep inertia. We analyzed 8 narrative reviews and 64 papers related to acute sleep inertia in healthy subjects.DISCUSSION: Sleep inertia is a multifactorial, complex process, and many different protocols have been conducted, with a low number of subjects, in noncontrolled laboratory designs, with questionnaires or cognitive tests that have not been replicated. Evidence suggests that waking after sleep loss, or from deeper stages of sleep, can exacerbate sleep inertia through complex interactions between awakening and sleep-promoting brain structures. Nevertheless, no meta-analyses are possible and extrapolation to pilots' performances is hypothetical. Studies in real life or simulated operational situations must be conducted to improve the description of the impact of sleep inertia and kinetics on pilots' performances. Taking rest or sleep time remains the main method for pilots to fight against fatigue and related decreases in performance. We propose proactive strategies to mitigate sleep inertia and improve alertness.Sauvet F, Beauchamps V, Cabon P. Sleep inertia in aviation. Aerosp Med Hum Perform. 2024; 95(4):206-213.

The Efficacy of a Multimodal Bedroom-Based 'Smart' Alarm System on Mitigating the Effects of Sleep Inertia

Previous work has demonstrated the modest impact of environmental interventions that manipulate lighting, sound, or temperature on sleep inertia symptoms. The current study sought to expand on previous work and measure the impact of a multimodal intervention that collectively manipulated light, sound, and ambient temperature on sleep inertia. Participants slept in the lab for four nights and were awoken each morning by either a traditional alarm clock or the multimodal intervention. Feelings of sleep inertia were measured each morning through Psychomotor Vigilance Test (PVT) assessments and ratings of sleepiness and mood at five time-points. While there was little overall impact of the intervention, the participant's chronotype and the length of the lighting exposure on intervention mornings both influenced sleep inertia symptoms. Moderate evening types who received a shorter lighting exposure (≤15 min) demonstrated more lapses relative to the control condition, whereas intermediate types exhibited a better response speed and fewer lapses. Conversely, moderate evening types who experienced a longer light exposure (>15 min) during the intervention exhibited fewer false alarms over time. The results suggest that the length of the environmental intervention may play a role in mitigating feelings of sleep inertia, particularly for groups who might exhibit stronger feelings of sleep inertia, including evening types.

An at-home evaluation of a light intervention to mitigate sleep inertia symptoms

OBJECTIVES

Under laboratory settings, light exposure upon waking at night improves sleep inertia symptoms. We investigated whether a field-deployable light source would mitigate sleep inertia in a real-world setting.

METHODS

Thirty-six participants (18 female; 26.6 years ± 6.1) completed an at-home, within-subject, randomized crossover study. Participants were awoken 45 minutes after bedtime and wore light-emitting glasses with the light either on (light condition) or off (control). A visual 5-minute psychomotor vigilance task, Karolinska sleepiness scale, alertness and mood scales, and a 3-minute auditory/verbal descending subtraction task were performed at 2, 12, 22, and 32 minutes after awakening. Participants then went back to sleep and were awoken after 45 minutes for the opposite condition. A series of mixed-effect models were performed with fixed effects of test bout, condition, test bout × condition, a random effect of the participant, and relevant covariates.

RESULTS

Participants rated themselves as more alert (p = .01) and energetic (p = .001) in the light condition compared to the control condition. There was no effect of condition for descending subtraction task outcomes when including all participants, but there was a significant improvement in descending subtraction task total responses in the light condition in the subset of participants waking from N3 (p = .03). There was a significant effect of condition for psychomotor vigilance task outcomes, with faster responses (p < .001) and fewer lapses (p < .001) in the control condition.

CONCLUSIONS

Our findings suggest that light modestly improves self-rated alertness and energy after waking at home regardless of sleep stage, with lower aggression and improvements to working memory only after waking from N3. Contrary to laboratory studies, we did not observe improved performance on the psychomotor vigilance task. Future studies should include measures of visual acuity and comfort to assess the feasibility of interventions in real-world settings.

Overview of the impact of sleep monitoring on optimal performance, immune system function and injury risk reduction in athletes: A narrative review

Sleep is essential for a range of physiological and mental functions in professional athletes. There is proof that athletes may experience lower quality and quantity of sleep. While adequate sleep has been shown to have restorative effects on the immune system and endocrine system, facilitate nervous system recovery and the metabolic cost of wakefulness, and play a significant role in learning, memory, and synaptic plasticity, which can affect sports recovery, injury risk reduction, and performance. Sports performance may suffer significantly from a lack of sleep, especially under maximal and long-term exercise. Due to the potential harm, these factors may do to an athlete's endocrine, metabolic, and nutritional health, sports performance is impacted by reduced sleep quality or quantity. There are several neurotransmitters associated with the sleep-wake cycle that have been discovered. They comprise cholinergic hormone, orexin, melanin, galanin, serotonin, gamma-aminobutyric acid, histamine, and serotonin. Therefore, dietary modifications that affect the neurotransmitters in the brain also may affect sleep; particularly for athletes who require more physical and psychological recovery owing to the tremendous physiological and psychological demands placed on them during training and performance. This review explores the variables that influence the quantity and quality of sleep-in populations of athletes and assesses their possible effects. In addition, several recommendations for improving sleep are presented. Even though there has been much research on variables that impact sleep, future studies may highlight the significance of these aspects for athletes.

Effects of short naps during simulated night shifts on alertness and cognitive performance in young adults

While short daytime naps have been found to provide alertness and performance benefits without inducing sleep inertia, the effects of a similar napping strategy during nights shifts are largely unknown. This study examined the effects of a 20-min nap (scheduled at 2:00 a.m.) during night shifts among 16 participants (mean [SD] age 22.0 [1.08] years) who worked in a simulated night shift from midnight (12:00 a.m.) to morning (ending at 6:00 or 8:00 a.m.). The participants underwent both a 'nap condition' and a 'no-nap condition' by engaging in repeated 10-min tasks (four-choice reaction time tasks and vigilance tasks) and 10-min rest. The results showed that compared to the no-nap condition, sleepiness was significantly lower in the nap condition between 3:20 and 5:20 a.m. (p < 0.05). The nap condition also yielded significantly better performance in the vigilance tasks between 2:40 and 5:40 a.m., except at 4:40 am (p < 0.05). However, no significant difference was found in sleepiness and performance in the vigilance task at 5:40 a.m. or immediately after the nap between the two conditions. The results showed that a 20-min nap at 2:00 a.m. did not induce sleep inertia upon waking. Furthermore, it mitigated sleepiness and sustained work performance for 3 h after the nap. However, the effect of napping was no longer observed near the end of the night shift. Considering risks of falling asleep while driving home from work that may cause a traffic accident, further research should examine ways to mitigate sleepiness after a night shift.

"Leave your smartphone out of bed": quantitative analysis of smartphone use effect on sleep quality

Smartphones have become an integral part of people's everyday lives. Smartphones are used across all household locations, including in the bed at night. Smartphone screens and other displays emit blue light, and exposure to blue light can affect one's sleep quality. Thus, smartphone use prior to bedtime could disrupt the quality of one's sleep, but research lacks quantitative studies on how smartphone use can influence sleep. This study combines smartphone application use data from 75 participants with sleep data collected by a wearable ring. On average, the participants used their smartphones in bed for 322.8 s (5 min and 22.8 s), with an IQR of 43.7-456. Participants spent an average of 42% of their time in bed using their smartphones (IQR of 5.87-55.5%). Our findings indicate that smartphone use in bed has significant adverse effects on sleep latency, awake time, average heart rate, and HR variability. We also find that smartphone use does not decrease sleep quality when used outside of bed. Our results indicate that intense smartphone use alone does not negatively affect well-being. Since all smartphone users do not use their phones in the same way, extending the investigation to different smartphone use types might yield more information than general smartphone use. In conclusion, this paper presents the first investigation of the association between smartphone application use logs and detailed sleep metrics. Our work also validates previous research results and highlights emerging future work.

Night shifts in interns: Effects of daytime napping on autonomic activity and cognitive function

Objective

Night shifts have adverse cognitive outcomes that might be attenuated by daytime napping. The neurovisceral integration model suggests that resting vagally mediated heart rate variability (vmHRV) is linked with cognitive function. This study investigated the relationship between resting vmHRV and cognitive function after different nap durations in interns after shift work.

Methods

A total of 105 interns were randomly allocated to one of three groups (non-nap, n = 35; 15-min nap, n = 35; 45-min nap, n = 35) to perform cognitive tests and resting vmHRV at 12:00, 15:00 and 18:00. Information processing (digit symbol substitution test; DSST), motor speed (finger tapping test; FTT), response selection (choice reaction time; CRT), and attention shifts (shifting attention test; SAT) were assessed. Resting vmHRV was assessed at baseline and during each cognitive task across groups.

Results

Compared with the non-nap control, the 15-min and 45-min naps improved all outcome measures (including subjective sleepiness and cognitive performance) at 15:00, with some benefits maintained at 18:00. The 15-min nap produced significantly greater benefits on the FTT at 15:00 after napping than did the 45-min nap. Resting vmHRV was significantly correlated with DSST and SAT performance. In addition, FTT performance was the only significant predictor of DSST performance across different nap durations.

Conclusion

Our results demonstrate links between daytime napping (in particular, a 15-min nap) and improved cognitive control in relation to autonomic activity after shift work in interns. These results indicated that autonomic activity when awake plays a crucial role in DSST and SAT performance and facilitated the understanding of differences in neurocognitive mechanisms underlying information processing after different nap durations.

Rise and shine: The use of polychromatic short-wavelength-enriched light to mitigate sleep inertia at night following awakening from slow-wave sleep

Sleep inertia is the brief period of performance impairment and reduced alertness experienced after waking, especially from slow-wave sleep. We assessed the efficacy of polychromatic short-wavelength-enriched light to improve vigilant attention, alertness and mood immediately after waking from slow-wave sleep at night. Twelve participants (six female, 23.3 ± 4.2 years) maintained an actigraphy-confirmed sleep schedule of 8.5 hr for 5 nights, and 5 hr for 1 night prior to an overnight laboratory visit. In the laboratory, participants were awakened from slow-wave sleep, and immediately exposed to either dim, red ambient light (control) or polychromatic short-wavelength-enriched light (light) for 1 hr in a randomized crossover design. They completed a 5-min Psychomotor Vigilance Task, the Karolinska Sleepiness Scale, and Visual Analogue Scales of mood at 2, 17, 32 and 47 min after waking. Following this testing period, lights were turned off and participants returned to sleep. They were awakened from their subsequent slow-wave sleep period and received the opposite condition. Compared with the control condition, participants exposed to light had fewer Psychomotor Vigilance Task lapses (χ² [1] = 5.285, p = 0.022), reported feeling more alert (Karolinska Sleepiness Scale: F_1,77  = 4.955, p = 0.029; Visual Analogue Scale_alert : F_1,77  = 8.226, p = 0.005), and reported improved mood (Visual Analogue Scale_cheerful : F_1,77  = 8.615, p = 0.004). There was no significant difference in sleep-onset latency between conditions following the testing period (t₁₀  = 1.024, p = 0.330). Our results suggest that exposure to polychromatic short-wavelength-enriched light immediately after waking from slow-wave sleep at night may help improve vigilant attention, subjective alertness, and mood. Future studies should explore the potential mechanisms of this countermeasure and its efficacy in real-world environments.

Effects of an afternoon nap on sustained attention and working memory: The role of physiological arousal and sleep variables

Taking a short midday nap has been associated with higher alertness and better cognitive task performance. Yet, the mechanisms associated with nap-dependent performance enhancement are unclear. The current study was conducted to explore the impact of physiological arousal during cognitive task and sleep architecture during a pre-task nap on post-nap behavioral outcomes. A within-subjects design (N = 18) was employed, in which participants either took a nap or remained awake for 40 min during the post-lunch period. The psychomotor vigilance test (PVT) and n-back task were administered to assess sustained attention and working memory, respectively, with each task including one block of easy trials and one block of difficult trials. Results showed that a short midday nap improved sustained attention but not working memory. In addition, a midday nap induced lower physiological arousal during the performance on both cognitive tasks, with relatively higher delta and lower beta activity. The relative power of theta and alpha were positively correlated with performance on the easy PVT, whereas the alpha power was negatively correlated with performance on the difficult PVT, and the theta power was negatively correlated with reaction speed in the n-back task regardless of the task difficulty. Meanwhile, the shorter total sleep time and longer time of wake after sleep onset were associated with the faster overall reaction speed in PVT easy trials. These findings suggested that both changes in physiological arousal and sleep variables might account for changes in task performance after a short midday nap.

Adenosine, caffeine, and sleep-wake regulation: state of the science and perspectives

For hundreds of years, mankind has been influencing its sleep and waking state through the adenosinergic system. For ~100 years now, systematic research has been performed, first started by testing the effects of different dosages of caffeine on sleep and waking behaviour. About 70 years ago, adenosine itself entered the picture as a possible ligand of the receptors where caffeine hooks on as an antagonist to reduce sleepiness. Since the scientific demonstration that this is indeed the case, progress has been fast. Today, adenosine is widely accepted as an endogenous sleep‐regulatory substance. In this review, we discuss the current state of the science in model organisms and humans on the working mechanisms of adenosine and caffeine on sleep. We critically investigate the evidence for a direct involvement in sleep homeostatic mechanisms and whether the effects of caffeine on sleep differ between acute intake and chronic consumption. In addition, we review the more recent evidence that adenosine levels may also influence the functioning of the circadian clock and address the question of whether sleep homeostasis and the circadian clock may interact through adenosinergic signalling. In the final section, we discuss the perspectives of possible clinical applications of the accumulated knowledge over the last century that may improve sleep‐related disorders. We conclude our review by highlighting some open questions that need to be answered, to better understand how adenosine and caffeine exactly regulate and influence sleep.

Planning Ability and Alertness After Nap Deprivation: Beneficial Effects of Acute Moderate-Intensity Aerobic Exercise Greater Than Sitting Naps

Nap deprivation is regarded as a sleep loss for habitual nappers. The beneficial effects of napping and moderate-intensity aerobic exercise on the reduction in planning ability following nighttime sleep deprivation have been proven. However, it is still unknown whether it can improve the performance decline caused by daytime nap deprivation in habitual nappers. Seventy-four healthy adults who had a long-term habit of taking naps were assigned to three interventions after receiving nap deprivation: (1) Control group (no intervention); (2) Nap group (15-min sitting naps); (3) Exercise group (15-min aerobic exercise), in which subjective alertness, mood, fatigue, and task performance in objective alertness (Psychomotor Vigilance Task, PVT) and planning ability (the Tower of London Task) were measured. Results showed that nap deprivation negatively influenced some performance on the psychomotor vigilance (i.e., response times and 10% slowest response time) and planning ability (i.e., planning time). And acute moderate-intensity aerobic exercise improved psychomotor alertness (i.e., response times) and planning ability (i.e., execution accuracy, execution time), a 15-min sitting naps only alleviated subjective fatigue, whereas some performance (i.e., response times) deteriorated when no intervention was used. These findings suggested that acute moderate-intensity aerobic exercise has a better restorative effect on the reduced planning ability and objective alertness due to nap deprivation compared to sitting naps.

"I Want to Be Safe and Not Still Half Asleep": Exploring Practical Countermeasures to Manage the Risk of Sleep Inertia for Emergency Service Personnel Using a Mixed Methods Approach

PURPOSE

The aim of this exploratory cross-sectional mixed methods study was to determine 1) whether sleep inertia, the temporary state of impaired vigilance performance upon waking, is perceived to be a concern by emergency service personnel, 2) what strategies are currently used by emergency service workplaces to manage sleep inertia, 3) the barriers to implementing reactive sleep inertia countermeasures, and 4) what strategies personnel suggest to manage sleep inertia.

PARTICIPANTS AND METHODS

A sample (n = 92) of employed and volunteer Australian emergency service personnel (fire and rescue, ambulance, police, state-based rescue and recovery personnel) completed an online survey. Data collected included demographic variables and work context, experiences of sleep inertia in the emergency role, barriers to sleep inertia countermeasures, and existing workplace sleep inertia countermeasures and recommendations. Quantitative data were analysed using descriptive statistics, and qualitative data were thematically analysed.

RESULTS

Approximately 67% of participants expressed concern about sleep inertia when responding in their emergency role. Despite this, there were few strategies to manage sleep inertia in the workplace. One major barrier identified was a lack of time in being able to implement sleep inertia countermeasures. Fatigue management strategies, such as reducing on-call periods, and operational changes, such as screening calls to reduce false alarms, were suggested by participants as potential strategies to manage sleep inertia.

CONCLUSION

Sleep inertia is a concern for emergency service personnel and thus more research is required to determine effective sleep inertia management strategies to reduce the risks associated with sleep inertia and improve personnel safety and those in their care. In addition, future studies could investigate strategies to integrate reactive sleep inertia countermeasures into the emergency response procedure.

The impact of a short burst of exercise on sleep inertia

STUDY OBJECTIVES

Determine whether 30 s (s) of exercise performed upon waking can reduce sleep inertia and accelerate an increase in the cortisol awakening response (CAR) and core body temperature (CBT), compared to when sedentary.

METHODS

Fifteen participants (mean age ± SD, 25.9 ± 5.9 years; six females) completed a counterbalanced, repeated measures, in-laboratory study involving three single experimental nights, each separated by a four-night recovery period. Participants were woken following a 2-h nap (2400-0200) and completed a cycling bout of high-intensity (30-s sprint), low-intensity (30 s at 60% maximum heart rate), or no exercise (sedentary). Sleep inertia testing (eight batteries, 15-min intervals) began immediately following and included measures of subjective sleepiness (Karolinska Sleepiness Scale) and cognitive performance tasks (psychomotor vigilance, serial addition and subtraction, and spatial configuration). CBT was measured continuously via an ingestible telemetric capsule. The CAR was determined using salivary cortisol samples collected at 0, 30 and 45 min post-waking. Data were analysed using mixed effects analysis of variance.

RESULTS

There was no difference in cognitive performance or CBT between conditions. Participants felt less sleepy in the high-intensity condition, followed by the low-intensity and sedentary conditions (p = .003). The CAR was greatest in the high-intensity condition, followed by the sedentary condition, and low-intensity condition (p < 0.001), with no differences between the low-intensity and sedentary conditions.

CONCLUSIONS

Those who exercise upon waking should be aware that while they may feel more alert, they may not be performing better than if they had not exercised. Future research should investigate whether exercise of different duration or timing may impact sleep inertia.

The Effect of Experimental Recuperative and Appetitive Post-lunch Nap Opportunities, With or Without Caffeine, on Mood and Reaction Time in Highly Trained Athletes

Purpose: To investigate the effects of placebo (PLA), 20 min nap opportunity (N20), 5mg·kg-1 of caffeine (CAF), and their combination (CAF+N20) on sleepiness, mood and reaction-time after partial sleep deprivation (PSD; 04h30 of time in bed; study 1 ) or after normal sleep night (NSN; 08h30 of time in bed; study 2 ). Methods: Twenty-three highly trained athletes ( study 1 ; 9 and study 2 ; 14) performed four test sessions (PLA, CAF, N20 and CAF+N20) in double-blind, counterbalanced and randomized order. Simple (SRT) and two-choice (2CRT) reaction time, subjective sleepiness (ESS) and mood state (POMS) were assessed twice, pre- and post-intervention. Results: SRT was lower (i.e., better performance) during CAF condition after PSD (pre: 336 ± 15 ms vs. post: 312 ± 9 ms; p < 0.001; d = 2.07; Δ% = 7.26) and NSN (pre: 350 ± 39 ms vs. post: 323 ± 32 ms; p < 0.001; d = 0.72; Δ% = 7.71) compared to pre-intervention. N20 decreased 2CRT after PSD (pre: 411 ± 13 ms vs. post: 366 ± 20 ms; p < 0.001; d = 2.89; Δ% = 10.81) and NSN (pre: 418 ± 29 ms vs. post: 375 ± 40 ms; p < 0.001; d = 1.23; Δ% = 10.23). Similarly, 2CRT was shorter during CAF+N20 sessions after PSD (pre: 406 ± 26 ms vs. post: 357 ± 17 ms; p < 0.001; d = 2.17; Δ% = 12.02) and after NSN (pre: 386 ± 33 ms vs. post: 352 ± 30 ms; p < 0.001; d = 1.09; Δ% = 8.68). After PSD, POMS score decreased after CAF (p < 0.001; d = 2.38; Δ% = 66.97) and CAF+N20 (p < 0.001; d = 1.68; Δ% = 46.68). However, after NSN, only N20 reduced POMS (p < 0.001; d = 1.05; Δ% = 78.65) and ESS (p < 0.01; d = 0.71; Δ% = 19.11). Conclusion: After PSD, all interventions reduced sleepiness and only CAF enhanced mood with or without napping. However, only N20 enhanced mood and reduced sleepiness after NSN. Caffeine ingestion enhanced SRT performance regardless of sleep deprivation. N20, with or without caffeine ingestion, enhanced 2CRT independently of sleep deprivation. This suggests a different mode of action of napping and caffeine on sleepiness, mood and reaction time.

Models for predicting sleep latency and sleep duration

STUDY OBJECTIVES

Planning effective sleep-wake schedules for civilian and military settings depends on the ability to predict the extent to which restorative sleep is likely for a specified sleep period. Here, we developed and validated two mathematical models, one for predicting sleep latency and a second for predicting sleep duration, as decision aids to predict efficacious sleep periods.

METHODS

We extended the Unified Model of Performance (UMP), a well-validated mathematical model of neurobehavioral performance, to predict sleep latency and sleep duration, which vary nonlinearly as a function of the homeostatic sleep pressure and the circadian rhythm. To this end, we used the UMP to predict the time course of neurobehavioral performance under different conditions. We developed and validated the models using experimental data from 317 unique subjects from 24 different studies, which included sleep conditions spanning the entire circadian cycle.

RESULTS

The sleep-latency and sleep-duration models accounted for 42% and 84% of the variance in the data, respectively, and yielded acceptable average prediction errors for planning sleep schedules (4.0 min for sleep latency and 0.8 h for sleep duration). Importantly, we identified conditions under which small shifts in sleep onset timing result in disproportionately large differences in sleep duration-knowledge that may be applied to improve performance, safety, and sustainability in civilian and military operations.

CONCLUSIONS

These models extend the capabilities of existing predictive fatigue-management tools, allowing users to anticipate the most opportune times to schedule sleep periods.

Caffeine Use or Napping to Enhance Repeated Sprint Performance After Partial Sleep Deprivation: Why Not Both?

PURPOSE

To compare the effect of a 20-minute nap opportunity (N20), a moderate dose of caffeine (CAF; 5 mg·kg-1), or a moderate dose of caffeine before N20 (CAF+N) as possible countermeasures to the decreased performance and the partial sleep deprivation-induced muscle damage.

METHODS

Nine male, highly trained judokas were randomly assigned to either baseline normal sleep night, placebo, N20, CAF, or CAF+N. Test sessions included the running-based anaerobic sprint test, from which the maximum (Pmax), mean (Pmean), and minimum (Pmin) powers were calculated. Biomarkers of muscle, hepatic, and cardiac damage and of enzymatic and nonenzymatic antioxidants were measured at rest and after the exercise.

RESULTS

N20 increased Pmax compared with placebo (P < .01, d = 0.75). CAF+N increased Pmax (P < .001, d = 1.5; d = 0.94), Pmin (P < .001, d = 2.79; d = 2.6), and Pmean (P < .001, d = 1.93; d = 1.79) compared with placebo and CAF, respectively. Postexercise creatine kinase increased whenever caffeine was added, that is, after CAF (P < .001, d = 1.19) and CAF+N (P < .001, d = 1.36). Postexercise uric acid increased whenever participants napped, that is, after N20 (P < .001, d = 2.19) and CAF+N (P < .001, d = 2.50) and decreased after CAF (P < .001, d = 2.96).

CONCLUSION

Napping improved repeated-sprint performance and antioxidant defense after partial sleep deprivation. Contrarily, caffeine increased muscle damage without improving performance. For sleep-deprived athletes, caffeine before a short nap opportunity would be more beneficial for repeated sprint performance than each treatment alone.

Sleep in older adolescents. Results from a large cross-sectional, population-based study

The aim of the present study was to describe sleep patterns in a large and representative sample of Norwegian adolescents. The sample included 4,010 first-year high school students, aged 16-17 years (54% female), who completed a web-based survey on sleep patterns. The process of going to sleep was addressed as a two-step sequence of (a) shuteye latency (interval from bedtime to shuteye time) and (b) sleep onset latency (interval from shuteye time to sleep onset). Results showed that 84.8% of the adolescents failed to obtain the recommended amount of sleep (8+ h) on schooldays, and 49.4% obtained less than 7 h. Mean bedtime on schooldays was 10:33 PM, with rise time 8:19 h later (time in bed). The adolescents reported long school-day shuteye latency (43 min), limiting sleep opportunity to 7:36 h. Sleep onset latency was 32 min and mean school-day sleep duration was only 6:43 h. On free days, 26.3% of the adolescents obtained less than 8 h of sleep, and 11.7% obtained less than 7 h. Mean bedtime was 00:33 AM, time in bed was 10:35 h, shuteye latency was 39 min and sleep onset latency was 24 min. Mean free-day sleep duration was 8:38 h. There were sex differences in several sleep parameters, including shuteye latency. The results indicate that the majority of Norwegian adolescents fail to obtain the recommended amount of sleep (8+ h) on schooldays. Long shuteye latency appears to be a main driver for short school-day sleep duration in adolescents.

Sleep and the athlete: narrative review and 2021 expert consensus recommendations

Elite athletes are particularly susceptible to sleep inadequacies, characterised by habitual short sleep (<7 hours/night) and poor sleep quality (eg, sleep fragmentation). Athletic performance is reduced by a night or more without sleep, but the influence on performance of partial sleep restriction over 1-3 nights, a more real-world scenario, remains unclear. Studies investigating sleep in athletes often suffer from inadequate experimental control, a lack of females and questions concerning the validity of the chosen sleep assessment tools. Research only scratches the surface on how sleep influences athlete health. Studies in the wider population show that habitually sleeping <7 hours/night increases susceptibility to respiratory infection. Fortunately, much is known about the salient risk factors for sleep inadequacy in athletes, enabling targeted interventions. For example, athlete sleep is influenced by sport-specific factors (relating to training, travel and competition) and non-sport factors (eg, female gender, stress and anxiety). This expert consensus culminates with a sleep toolbox for practitioners (eg, covering sleep education and screening) to mitigate these risk factors and optimise athlete sleep. A one-size-fits-all approach to athlete sleep recommendations (eg, 7-9 hours/night) is unlikely ideal for health and performance. We recommend an individualised approach that should consider the athlete's perceived sleep needs. Research is needed into the benefits of napping and sleep extension (eg, banking sleep).

Alarm Tones, Voice Warnings, and Musical Treatments: A Systematic Review of Auditory Countermeasures for Sleep Inertia in Abrupt and Casual Awakenings

Sleep inertia is a measurable decline in cognition some people experience upon and following awakening. However, a systematic review of the current up to date evidence of audio as a countermeasure has yet to be reported. Thus, to amend this gap in knowledge, the authors conducted this systematic review beginning with searches in three primary databases for studies published between the inception date of each journal and the year 2020. Search terms contained “Sleep Inertia” paired with: “Sound”; “Noise”; “Music”; “Alarm”; “Alarm Tone”; “Alarm Sound”; “Alarm Noise”; “Alarm Music”; “Alarm Clock”; “Fire Alarm”, and “Smoke Alarm”. From 341 study results, twelve were identified for inclusion against a priori conditions. A structured narrative synthesis approach generated three key auditory stimulus themes-(i) Noise, (ii) Emergency tone sequences; Voice Alarms and Hybrids, and (iii) Music. Across themes, participants have been assessed in two situational categories: emergency, and non-emergency awakenings. The results indicate that for children awakening in emergency conditions, a low pitch alarm or voice warnings appear to be more effective in counteracting the effects of sleep inertia than alarms with higher frequencies. For adults abruptly awakened, there is insufficient evidence to support firm conclusions regarding alarm types and voice signals. Positive results have been found in non-emergency awakenings for musical treatments in adults who preferred popular music, and alarms with melodic qualities. The results observed reflect the potential for sound, voice, and musical treatments to counteract sleep inertia post-awakening, and emphasize the requirements for further research in this domain.

Safety implications of fatigue and sleep inertia for emergency services personnel

Emergency services present a unique operational environment for the management of fatigue and sleep inertia. Communities request and often expect the provision of emergency services on a 24/7/365 basis. This can result in highly variable workloads and/or significant need for on-demand or on-call working time arrangements. In turn, the management of fatigue-related risk requires a different approach than in other more predictable shift working sectors (e.g., mining and manufacturing). The aim of this review is to provide a comprehensive overview of fatigue risk management that is accessible to regulators, policy makers and organisations in the emergency services sector. The review outlines the unique fatigue challenges in the emergency services sector, examines the current scientific and policy consensus around managing fatigue and sleep inertia, and finally discusses strategies that emergency services organisations can use to minimise the risks associated with fatigue and sleep inertia.

Auditory Countermeasures for Sleep Inertia: Exploring the Effect of Melody and Rhythm in an Ecological Context

Sleep inertia is a decline in cognition one may experience upon and following awakening. A recent study revealed that an alarm sound perceived as melodic by participants displayed a significant relationship to reports of reductions in perceived sleep inertia. This current research builds on these findings by testing the effect melody and rhythm exhibit on sleep inertia for subjects awakening in their habitual environments. Two test Groups (A and B; N = 10 each) completed an online psychomotor experiment and questionnaire in two separate test sessions immediately following awakening from nocturnal sleep. Both groups responded to a control stimulus in the first session, while in the second session, Group A experienced a melodic treatment, and Group B a rhythmic treatment. The results show that the melodic treatment significantly decreased attentional lapses, false starts, and had a significantly improved psychomotor vigilance test (PVT) performance score than the control. There was no significant result for reaction time or response speed. Additionally, no significant difference was observed for all PVT metrics between the control-rhythmic conditions. The results from this analysis support melodies' potential to counteract symptoms of sleep inertia by the observed increase in participant vigilance following waking from nocturnal sleep.

Exercising Caution Upon Waking-Can Exercise Reduce Sleep Inertia?

Sleep inertia, the transitional state of reduced alertness and impaired cognitive performance upon waking, is a safety risk for on-call personnel who can be required to perform critical tasks soon after waking. Sleep inertia countermeasures have previously been investigated; however, none have successfully dissipated sleep inertia within the first 15 min following waking. During this time, on-call personnel could already be driving, providing advice, or performing other safety-critical tasks. Exercise has not yet been investigated as a sleep inertia countermeasure but has the potential to stimulate the key physiological mechanisms that occur upon waking, including changes in cerebral blood flow, the cortisol awakening response, and increases in core body temperature. Here, we examine these physiological processes and hypothesize how exercise can stimulate them, positioning exercise as an effective sleep inertia countermeasure. We then propose key considerations for research investigating the efficacy of exercise as a sleep inertia countermeasure, including the need to determine the intensity and duration of exercise required to reduce sleep inertia, as well as testing the effectiveness of exercise across a range of conditions in which the severity of sleep inertia may vary. Finally, practical considerations are identified, including the recommendation that qualitative field-based research be conducted with on-call personnel to determine the potential constraints in utilizing exercise as a sleep inertia countermeasure in real-world scenarios.

Does upper-body elevation affect sleepiness and memories of hypnagogic images after short daytime naps?

The present study aimed to examine the effects of a somatosensory stimulus on sleepiness and memories of hypnagogic imagery during short daytime naps. Participants experienced two daytime nap conditions: (1) a somatosensory stimulus was created by raising the upper part of the bed 20 min after turning off the light and (2) a somatosensory stimulus was not created; the angle of the upper part of the bed remained flat. Approximately 20 min and 30 s after turning off the light, participants were awakened and questioned regarding their subjective sleepiness and the presence or absence of hypnagogic imagery. Results showed that subjective sleepiness following the nap was reduced only in the raised condition, and hypnagogic imagery in the raised condition was lower than that in the flat condition. These findings may provide insight on developing new techniques for improving subjective conditions after awakening.

Alarm tones, music and their elements: Analysis of reported waking sounds to counteract sleep inertia

Sleep inertia is a potentially dangerous reduction in human alertness and occurs 0-4 hours after waking. The type of sound people set as their alarm for waking has been shown to reduce the effects of sleep inertia, however, the elemental musical factors that underpin these waking sounds and their relationships remain unclear. The goal of this research is to understand how a particular sound or music chosen to assist waking may counteract sleep inertia, and more specifically, what elements of these sounds may contribute to its reduction. Through an anonymous, self-report online questionnaire, fifty participants (N = 50) reported attributes of their preferred waking sound, their feeling towards the waking sound, and perceived sleep inertia after waking. This data enabled the analysis and comparison between these responses to identify statistically significant relationships. Our results did not return any significant association between sleep inertia and the reported waking sound type, nor the subject's feeling towards their sound. However, the analysis did reveal that a sound which is ranked as melodic by participants shows a significant relationship to reports of reductions in perceived sleep inertia, and in contrast, sound rated as neutral (neither unmelodic nor melodic) returns a significant relationship to the reports of increases in perceived sleep inertia. Additionally, our secondary analysis revealed that a sound rated as melodic is considered to be more rhythmic than a melodically neutral interpretation. Together these findings raise questions regarding the impact melody and rhythm may hold with respect to sleep inertia intensity. Considering that the implementation of auditory assisted awakening is a common occurrence, the musical elements of a chosen waking sound may be an area to further interrogate with respect to counteracting sleep inertia.

Sleep inertia: current insights

Sleep inertia, or the grogginess felt upon awakening, is associated with significant cognitive performance decrements that dissipate as time awake increases. This impairment in cognitive performance has been observed in both tightly controlled in-laboratory studies and in real-world scenarios. Further, these decrements in performance are exaggerated by prior sleep loss and the time of day in which a person awakens. This review will examine current insights into the causes of sleep inertia, factors that may positively or negatively influence the degree of sleep inertia, the consequences of sleep inertia both in the laboratory and in real-world settings, and lastly discuss potential countermeasures to lessen the impact of sleep inertia.

Fatigue Risk Management: The Impact of Anesthesiology Residents' Work Schedules on Job Performance and a Review of Potential Countermeasures

Long duty periods and overnight call shifts impair physicians' performance on measures of vigilance, psychomotor functioning, alertness, and mood. Anesthesiology residents typically work between 64 and 70 hours per week and are often required to work 24 hours or overnight shifts, sometimes taking call every third night. Mitigating the effects of sleep loss, circadian misalignment, and sleep inertia requires an understanding of the relationship among work schedules, fatigue, and job performance. This article reviews the current Accreditation Council for Graduate Medical Education guidelines for resident duty hours, examines how anesthesiologists' work schedules can affect job performance, and discusses the ramifications of overnight and prolonged duty hours on patient safety and resident well-being. We then propose countermeasures that have been implemented to mitigate the effects of fatigue and describe how training programs or practice groups who must work overnight can adapt these strategies for use in a hospital setting. Countermeasures include the use of scheduling interventions, strategic naps, microbreaks, caffeine use during overnight and extended shifts, and the use of bright lights in the clinical setting when possible or personal blue light devices when the room lights must be turned off. Although this review focuses primarily on anesthesiology residents in training, many of the mitigation strategies described here can be used effectively by physicians in practice.

Chronic sleep restriction greatly magnifies performance decrements immediately after awakening

STUDY OBJECTIVES

Sleep inertia, subjectively experienced as grogginess felt upon awakening, causes cognitive performance impairments that can require up to 1.5 hr to dissipate. It is unknown, however, how chronic sleep restriction (CSR) influences the magnitude and duration of sleep inertia-related performance deficits.

METHODS

Twenty-six healthy participants were enrolled in one of two in-laboratory sleep restriction protocols (one 32 day randomized control and one 38 day protocol) that separated the influence of sleep and circadian effects on performance using different "day"-lengths (20 and 42.85 hr day-lengths, respectively). The sleep opportunity per 24 hr day was the equivalent of 5.6 hr for each CSR condition and 8 hr for the Control condition. Participant's performance and subjective sleepiness were assessed within ~2 min after electroencephalogram-verified awakening and every 10 min thereafter for 70 min to evaluate performance and subjective sleepiness during sleep inertia.

RESULTS

Performance within 2 min of awakening was ~10% worse in CSR conditions compared with Control and remained impaired across the dissipation of sleep inertia in the CSR conditions when compared with Control. These impairments in performance during sleep inertia occurred after only chronic exposure to sleep restriction and were even worse after awakenings during the biological nighttime. Interestingly, despite differences in objective performance, there were no significant differences between groups in subjective levels of sleepiness during sleep inertia.

CONCLUSIONS

CSR worsens sleep inertia, especially for awakenings during the biological night. These findings are important for individuals needing to perform tasks quickly upon awakening, particularly those who obtain less than 6 hr of sleep on a nightly basis.

CLINICAL TRIAL

The study "Sleep Duration Required to Restore Performance During Chronic Sleep Restriction" was registered as a clinical trial (#NCT01581125) at clinicaltrials.gov (https://clinicaltrials.gov/ct2/show/NCT01581125?term=NCT01581125.&rank=1).

Distal skin vasodilation in sleep preparedness, and its impact on thermal status in preterm neonates

OBJECTIVE

Prior to sleep onset in human adults, distal body temperatures change progressively from wakefulness levels (low skin temperatures and a high core temperature) to sleep levels (high skin temperatures and a low core temperature) due to distal skin vasodilation and greater body cooling. It is not known whether this sleep preparedness exists in preterm neonates, even though sleep has a key role in neonatal health and neurodevelopment. The present study's objectives were to determine whether sleep preparedness (as observed in adults) can be evidenced in preterm neonates, and to assess repercussions on thermal stress.

METHODS

During a 12-h night-time polysomnography session, skin temperatures (recorded with an infrared camera), sleep, and wakefulness episodes were measured in 18 nine-day-old preterm neonates.

RESULTS

Fifteen wakefulness episodes were considered. Our results highlighted significant pre-sleep distal skin vasodilation (mainly at the foot: an increase of 0.38 °C in the 20 min preceding sleep onset) for the first time in preterm neonates. This vasodilation occurred even though (1) most factors known to influence pre-sleep vasodilation in adults were not present in these neonates, and (2) the neonates were nursed in a nearly constant thermal environment. The vasodilatation-related increase in body heat loss corresponded to a 0.15°C/h fall in mean body temperature (calculated using partitional calorimetry).

CONCLUSION

Compensation for this body heat loss and the maintenance of body homeothermia would require a 4% increase in metabolic heat production. In neonates, this type of energy expenditure cannot be maintained for a long period of time.

Effects of red light on sleep inertia

Introduction: Sleep inertia, broadly defined as decrements in performance and lowering of alertness following waking, lasts for durations ranging between 1 min and 3 hrs. This study investigated whether, compared to a dim light condition (the control), exposure to long-wavelength (red) light delivered to closed eyelids during sleep (red light mask) and to eyes open upon waking (red light goggles) reduced sleep inertia. Methods: Thirty participants (18 females, 12 males; mean age=30.4 years [SD 13.7]) completed this crossover, within-subjects, counterbalanced design study. Self-reported measures of sleepiness and objective measures of auditory performance and cortisol levels were collected on 3 Friday nights over the course of 3 consecutive weeks. Results: Performance improved significantly during the 30-min data collection period in all experimental conditions. Subjective sleepiness also decreased significantly with time awake in all experimental conditions. As hypothesized, performance of some tasks was significantly better in the red light mask condition than in the dim light condition. Performance scores in the red light goggles condition improved significantly after a few minutes of wearing the light goggles. Discussion: The results show that saturated red light delivered through closed eyelids at levels that do not suppress melatonin can be used to mitigate sleep inertia upon waking.

Fatigue-related risk management in the emergency department: a focus-group study

Fatigue has major implications on both patient safety and healthcare practitioner's well-being. Traditionally, two approaches can be used to reduce fatigue-related risk: reducing the likelihood of a fatigued operator working (i.e. fatigue reduction), or reducing the likelihood that a fatigued operator will make an error (i.e. fatigue proofing). Recent progress mainly focussed on fatigue reduction strategies such as reducing work hours. Yet it has to be recognized that such approach has not wholly overcome the experience of fatigue. Our purpose is to investigate individual proofing and reduction strategies used by emergency physicians to manage fatigue-related risk. 25 emergency physicians were recruited for the study. Four focus groups were formed which consisted of an average of six individuals. Qualitative data were collected using a semi-structured discussion guide unfolding in two parts. First, the participants were asked to describe how on-the-job fatigue affected their efficiency at work. A mind map was progressively drawn based upon the participants' perceived effects of fatigue. Second, participants were asked to describe any strategies they personally used to cope with these effects. We used inductive qualitative content analysis to reveal content themes for both fatigue effects and strategies. Emergency physicians reported 28 fatigue effects, 12 reduction strategies and 21 proofing strategies. Content analysis yielded a further classification of proofing strategies into self-regulation, task re-allocation and error monitoring strategies. There is significant potential for the development of more formal processes based on physicians' informal strategies.

The Concept of Qailulah (Midday Napping) from Neuroscientific and Islamic Perspectives

Napping/siesta during the day is a phenomenon, which is widely practised in the world. However, the timing, frequency, and duration may vary. The basis of napping is also diverse, but it is mainly done for improvement in alertness and general well-being. Neuroscience reveals that midday napping improves memory, enhances alertness, boosts wakefulness and performance, and recovers certain qualities of lost night sleep. Interestingly, Islam, the religion of the Muslims, advocates midday napping primarily because it was a practice preferred by Prophet Muhammad (pbuh). The objectives of this review were to investigate and compare identical key points on focused topic from both neuroscientific and Islamic perspectives and make recommendations for future researches.

Using relaxation techniques to improve sleep during naps

Insufficient sleep is a common occurrence in occupational settings (e.g. doctors, drivers, soldiers). The resulting sleep debt can lead to daytime sleepiness, fatigue, mood disorder, and cognitive deficits as well as altered vascular, immune and inflammatory responses. Short daytime naps have been shown to be effective at counteracting negative outcomes related to sleep debt with positive effects on daytime sleepiness and performance after a normal or restricted night of sleep in laboratory settings. However, the environmental settings in the workplace and the emotional state of workers are generally not conducive to beneficial effects. Here, we tested whether relaxation techniques (RT) involving hypnosis might increase total sleep time (TST) and/or deepen sleep. In this study, eleven volunteers (aged 37-52) took six early-afternoon naps (30 min) in their occupational workplace, under two different conditions: control 'Naps' or 'Naps + RT' with a within-subjects design. Our results demonstrate that adding RT to naps changes sleep architecture, with a significant increase in the TST, mostly due to N2 sleep stage (and N3, to a lesser extent). Therefore, the deepening of short naps with RT involving hypnosis might be a successful non-pharmacological way to extend sleep duration and to deepen sleep in occupational settings.

Sleep and Alertness in Medical Interns and Residents: An Observational Study on the Role of Extended Shifts

Study Objectives

Fatigue from sleep loss is a risk to physician and patient safety, but objective data on physician sleep and alertness on different duty hour schedules is scarce. This study objectively quantified differences in sleep duration and alertness between medical interns working extended overnight shifts and residents not or rarely working extended overnight shifts.

Methods

Sleep-wake activity of 137 interns and 87 PGY-2/3 residents on 2-week Internal Medicine and Oncology rotations was assessed with wrist-actigraphy. Alertness was assessed daily with a brief Psychomotor Vigilance Test (PVT) and the Karolinska Sleepiness Scale.

Results

Interns averaged 6.93 hours (95% confidence interval [CI] 6.84-7.03 hours) sleep per 24 hours across shifts, significantly less than residents not working overnight shifts (7.18 hours, 95% CI 7.06-7.30 hours, p = .007). Interns obtained on average 2.19 hours (95% CI 2.02-2.36 hours) sleep during on-call nights (17.5% obtained no sleep). Alertness was significantly lower on mornings after on-call nights compared to regular shifts (p < .001). Naps between 9 am and 6 pm on the first day post-call were frequent (90.8%) and averaged 2.84 hours (95% CI 2.69-3.00 hours), but interns still slept 1.66 hours less per 24 hours (95% CI 1.56-1.76 hours) compared to regular shift days (p < .001). Sleep inertia significantly affected alertness in the 60 minutes after waking on-call.

Conclusions

Extended overnight shifts increase the likelihood of chronic sleep restriction in interns. Reduced levels of alertness after on-call nights need to be mitigated. A systematic comparison of sleep, alertness, and safety outcomes under current and past duty hour rules is encouraged.

Time to wake up: reactive countermeasures to sleep inertia

Sleep inertia is the period of impaired performance and grogginess experienced after waking. This period of impairment is of concern to workers who are on-call, or nap during work hours, and need to perform safety-critical tasks soon after waking. While several studies have investigated the best sleep timing and length to minimise sleep inertia effects, few have focused on countermeasures -especially those that can be implemented after waking (i.e. reactive countermeasures). This structured review summarises current literature on reactive countermeasures to sleep inertia such as caffeine, light, and temperature and discusses evidence for the effectiveness and operational viability of each approach. Current literature does not provide a convincing evidence-base for a reactive countermeasure. Caffeine is perhaps the best option, although it is most effective when administered prior to sleep and is therefore not strictly reactive. Investigations into light and temperature have found promising results for improving subjective alertness; further research is needed to determine whether these countermeasures can also attenuate performance impairment. Future research in this area would benefit from study design features highlighted in this review. In the meantime, it is recommended that proactive sleep inertia countermeasures are used, and that safety-critical tasks are avoided immediately after waking.

The effect of sleep on motor learning in the aging and stroke population - a systematic review

There is extensive evidence for positive effects of sleep on motor learning in young individuals; however, the effects of sleep on motor learning in people with stroke and in healthy older individuals are not well understood. The aim of this systematic review was to quantify the association between sleep and procedural memory performance - a marker for motor learning - in healthy older people and people with stroke. After searches in PubMed, Medline and Embase fourteen studies, including 44 subjects after stroke and 339 healthy older participants were included. Overall, sleep was found to enhance motor performance in people after stroke in comparison to an equivalent time of wakefulness. In addition, although evidence is limited, sleep only enhanced motor performance in people after stroke and not in age-matched healthy older adults. In older adults the effect of a sleep intervention did - in general - not differ from equivalent periods of wakefulness. Tasks with whole hand or whole body movements could show significant changes. The results suggest a delayed retention effect after longer breaks including sleep, hinting towards a changed learning strategy as a result of aging. Current evidence for sleep dependent learning in people after stroke is promising, however sparse.

Sleep inertia during a simulated 6-h on/6-h off fixed split duty schedule

Sleep inertia is a safety concern for shift workers returning to work soon after waking up. Split duty schedules offer an alternative to longer shift periods, but introduce additional wake-ups and may therefore increase risk of sleep inertia. This study investigated sleep inertia across a split duty schedule. Sixteen participants (age range 21-36 years; 10 females) participated in a 9-day laboratory study with two baseline nights (10 h time in bed, [TIB]), four 24-h periods of a 6-h on/6-h off split duty schedule (5-h TIB in off period; 10-h TIB per 24 h) and two recovery nights. Two complementary rosters were evaluated, with the timing of sleep and wake alternating between the two rosters (2 am/2 pm wake-up roster versus 8 am/8 pm wake-up roster). At 2, 17, 32 and 47 min after scheduled awakening, participants completed an 8-min inertia test bout, which included a 3-min psychomotor vigilance test (PVT-B), a 3-min Digit-Symbol Substitution Task (DSST), the Karolinska Sleepiness Scale (KSS), and the Samn-Perelli Fatigue Scale (SP-Fatigue). Further testing occurred every 2 h during scheduled wakefulness. Performance was consistently degraded and subjective sleepiness/fatigue was consistently increased during the inertia testing period as compared to other testing times. Morning wake-ups (2 am and 8 am) were associated with higher levels of sleep inertia than later wake-ups (2 pm and 8 pm). These results suggest that split duty workers should recognise the potential for sleep inertia after waking, especially during the morning hours.

Daytime sleep has no effect on the time course of motor sequence and visuomotor adaptation learning

Sleep has previously been claimed to be essential for the continued learning processes of declarative information as well as procedural learning. This study was conducted to examine the importance of sleep, especially the effects of midday naps, on motor sequence and visuomotor adaptation learning. Thirty-five (27 females) healthy, young adults aged between 18 and 30years of age participated in the current study. Addressing potential differences in explicit sequence and motor adaptation learning participants were asked to learn both, a nine-element explicit sequence and a motor adaptation task, in a crossover fashion on two consecutive days. Both tasks were performed with their non-dominant left hand. Prior to learning, each participant was randomized to one of three interventions; (1) power nap: 10-20min sleep, (2) long nap: 50-80min sleep or (3) a 45-min wake-condition. Performance of the motor learning task took place prior to and after a midday rest period, as well as after a night of sleep. Both sleep conditions were dominated by Stage N2 sleep with embedded sleep spindles, which have been described to be associated with enhancement of motor performance. Significant performance changes were observed in both tasks across all interventions (sleep and wake) confirming that learning took place. In the present setup, the magnitude of motor learning was not sleep-dependent in young adults - no differences between the intervention groups (short nap, long nap, no nap) could be found. The effect of the following night of sleep was not influenced by the previous midday rest or sleep period. This finding may be related to the selectiveness of the human brain enhancing especially memory being thought of as important in the future. Previous findings on motor learning enhancing effects of sleep, especially of daytime sleep, are challenged.

A 30-Minute, but Not a 10-Minute Nighttime Nap is Associated with Sleep Inertia

STUDY OBJECTIVES

To assess sleep inertia following 10-min and 30-min naps during a simulated night shift.

METHODS

Thirty-one healthy adults (aged 21-35 y; 18 females) participated in a 3-day laboratory study that included one baseline (BL) sleep (22:00-07:00) and one experimental night involving randomization to either: total sleep deprivation (NO-NAP), a 10-min nap (10-NAP) or a 30-min nap (30-NAP). Nap opportunities ended at 04:00. A 3-min psychomotor vigilance task (PVT-B), digit-symbol substitution task (DSST), fatigue scale, sleepiness scale, and self-rated performance scale were undertaken pre-nap (03:00) and at 2, 17, 32, and 47 min post-nap.

RESULTS

The 30-NAP (14.7 ± 5.7 min) had more slow wave sleep than the 10-NAP (0.8 ± 1.5 min; P < 0.001) condition. In the NO-NAP condition, PVT-B performance was worse than pre-nap (4.6 ± 0.3 1/sec) at 47 min post-nap (4.1 ± 0.4 1/sec; P < 0.001). There was no change across time in the 10-NAP condition. In the 30-NAP condition, performance immediately deteriorated from pre-nap (4.3 ± 0.3 1/sec) and was still worse at 47 min post-nap (4.0 ± 0.5 1/sec; P < 0.015). DSST performance deteriorated in the NO-NAP (worse than pre-nap from 17 to 47 min; P < 0.008), did not change in the 10-NAP, and was impaired 2 min post-nap in the 30-NAP condition (P = 0.028). All conditions self-rated performance as better than pre-nap for all post-nap test points (P < 0.001).

CONCLUSIONS

This study is the first to show that a 10-min (but not a 30-min) nighttime nap had minimal sleep inertia and helped to mitigate short-term performance impairment during a simulated night shift. Self-rated performance did not reflect objective performance following a nap.

Hypersomnia subtypes, sleep and relapse in bipolar disorder

BACKGROUND

Though poorly defined, hypersomnia is associated with negative health outcomes and new-onset and recurrence of psychiatric illness. Lack of definition impedes generalizability across studies. The present research clarifies hypersomnia diagnoses in bipolar disorder by exploring possible subgroups and their relationship to prospective sleep data and relapse into mood episodes.

METHOD

A community sample of 159 adults (aged 18-70 years) with bipolar spectrum diagnoses, euthymic at study entry, was included. Self-report inventories and clinician-administered interviews determined features of hypersomnia. Participants completed sleep diaries and wore wrist actigraphs at home to obtain prospective sleep data. Approximately 7 months later, psychiatric status was reassessed. Factor analysis and latent profile analysis explored empirical groupings within hypersomnia diagnoses.

RESULTS

Factor analyses confirmed two separate subtypes of hypersomnia ('long sleep' and 'excessive sleepiness') that were uncorrelated. Latent profile analyses suggested a four-class solution, with 'long sleep' and 'excessive sleepiness' again representing two separate classes. Prospective sleep data suggested that the sleep of 'long sleepers' is characterized by a long time in bed, not long sleep duration. Longitudinal assessment suggested that 'excessive sleepiness' at baseline predicted mania/hypomania relapse.

CONCLUSIONS

This study is the largest of hypersomnia to include objective sleep measurement, and refines our understanding of classification, characterization and associated morbidity. Hypersomnia appears to be comprised of two separate subgroups: long sleep and excessive sleepiness. Long sleep is characterized primarily by long bedrest duration. Excessive sleepiness is not associated with longer sleep or bedrest, but predicts relapse to mania/hypomania. Understanding these entities has important research and treatment implications.

Natural light exposure, sleep and depression among day workers and shiftworkers at arctic and equatorial latitudes

OBJECTIVES

This study aimed to investigate the relationship between individual natural light exposure, sleep need, and depression at two latitudes, one extreme with a few hours of light per day during winter, and the other with equal hours of light and darkness throughout the year.

METHODS

This cross-sectional study included a sample of Brazilian workers (Equatorial, n = 488 workers) and a Swedish sample (Arctic, n = 1,273).

RESULTS

The reported mean total natural light exposure per 4-week cycle differed significantly between the Equatorial and Arctic regions. However, shiftworkers from both sites reported similar hours of natural light exposure. Short light exposure was a predictor for insufficient sleep.

CONCLUSION

Reduced exposure to natural light appears to increase the perception of obtaining insufficient sleep. Arctic workers were more prone to develop depression than Equatorial workers.

Driving fatigue in professional drivers: a survey of truck and taxi drivers

OBJECTIVES

Fatigue among truck drivers has been studied extensively; however, less is known regarding the fatigue experience of taxi drivers in heavily populated metropolitan areas. This study aimed to compare the differences and similarities between truck and taxi driver fatigue to provide implications for the fatigue management and education of professional drivers.

METHODS

A sample of 274 truck drivers and 286 taxi drivers in Beijing was surveyed via a questionnaire, which included items regarding work characteristics, fatigue experience, accident information, attitude toward fatigue, and methods of counteracting fatigue.

RESULTS

Driver fatigue was prevalent among professional drivers, and it was even more serious for taxi drivers. Taxi drivers reported more frequent fatigue experiences and were involved in more accidents. Among the contributing factors to fatigue, prolonged driving time was the most important factor identified by both driver groups. Importantly, the reason for the engagement in prolonged driving was neither due to the lack of awareness concerning the serious outcome of fatigue driving nor because of their poor detection of fatigue. The most probable reason was the optimism bias, as a result of which these professional drivers thought that fatigue was more serious for other drivers than for themselves, and they thought that they were effective in counteracting the effect of fatigue on their driving performance. Moreover, truck drivers tended to employ methods that require stopping to counteract fatigue, whereas taxi drivers preferred methods that were simultaneous with driving. Although both driver groups considered taking a nap as one of the most effective means to address fatigue, this method was not commonly used. Interestingly, these drivers were aware that the methods they frequently used were not the most effective means to counteract fatigue.

CONCLUSIONS

This study provides knowledge on truck and taxi drivers' characteristics in fatigue experience, fatigue attitude, and fatigue countermeasures, and these findings have practical implications for the fatigue management and education of professional drivers.