Operational assessment of the 5-h on/10-h off watchstanding schedule on a US Navy ship: sleep patterns, mood and psychomotor vigilance performance of crewmembers in the nuclear reactor department

Changes in higher order cognitive function between four watch keeping schedules

Maritime industries utilize many different watch keeping schedules to maintain vigilance and crew safety around the clock. These schedules can be fatiguing, negatively impacting vigilant attention. This has led to the consideration of schedules that might allow for more sleep time, but how these schedules impact higher order cognitive function remains unclear. These schedules require assessment with tasks that are relevant to real-world operations on maritime vessels. This study investigated the effect of four schedules on higher order cognitive function. N = 27 (16 female) participants were recruited to a 10-day laboratory study, comparing four schedules. The schedules investigated were eight-on/eight-off/four-on/four-off (8/8/4/4) with sleep from 09:30 to 16:00 (condition A); six-on/six-off (6/6) with sleep from 08:30 to 12:30 and 21:30 to 00:00 (condition B); four-on/four-off (4/4/4/4/4/4) with sleep from 18:00 to 00:30 (condition C); and four-on/four-off (4/4/4/4/4/4) with sleep from 01:30 to 08:00 (condition D). Higher order cognitive function was assessed 2-3× daily whilst "on watch" using tests of visual scanning, learning, working memory, mental flexibility, and visuomotor control. Conditions were ranked and stability of performance on watch was compared between conditions using Kruskal-Wallis tests. Cognitive function within condition B was ranked the worst for most of the tasks. However, the stability of higher order cognitive function was poorest across the waking day within condition A. These findings highlight the variability in cognitive capacities during different watch keeping schedules.

Advancing a U.S. navy shipboard infrastructure for sleep monitoring with wearable technology

Development of fatigue management solutions is critical to U.S. Navy populations. This study explored the operational feasibility and acceptability of commercial wearable devices (Oura Ring and ReadiBand) in a warship environment with 845 Sailors across five ship cohorts during at-sea operations ranging from 10 to 31 days. Participants were required to wear both devices and check-in daily with research staff. Both devices functioned as designed in the environment and reliably collected sleep-wake data. Over 10,000 person-days at-sea, overall prevalence of Oura and ReadiBand use was 69% and 71%, respectively. Individual use rates were 71 ± 38% of days underway for Oura and 59 ± 34% for ReadiBand. Analysis of individual factors showed increasing device use and less device interference with age, and more men than women found the devices comfortable. This study provides initial support that commercial wearables can contribute to infrastructures for operational fatigue management in naval environments.

Sleepy and grumpy go hand in hand for US Navy Sailors

Study Objectives

The study explores how sleep, sleep-related practices, and behaviors, in addition to various demographic and occupational characteristics, are related to overall mood of US Navy sailors when they are underway.

Methods

Longitudinal assessment of US Navy sailors performing their underway duties (N = 873, 79.2% males, median age 25 years). Participants completed standardized questionnaires, wore wrist-worn actigraphs, and completed daily activity logs.

Results

Sailors who reported worse profile of mood states (POMS) total mood disturbance scores had shorter sleep duration, worse sleep quality, and more episodes of split sleep. The group with worse mood also reported more symptoms of excessive daytime sleepiness as well as more symptoms of insomnia. In addition to sleep results, sailors with worse mood also tended to be younger, more likely to use nicotine and tobacco products, and less likely to have an exercise routine when compared to sailors with better POMS scores. Finally, the group with worse POMS scores included more enlisted personnel, tended to work more hours per day, and were more likely to stand watch-especially on rotating watch schedules.

Conclusions

The results found significant associations between the sleep practices and mood of sailors aboard US Navy ships. Numerous other demographic and occupational factors were also strongly associated with mood. This paper is part of the Sleep and Circadian Rhythms: Management of Fatigue in Occupational Settings Collection.

Steps toward developing a comprehensive fatigue monitoring and mitigation solution: perspectives from a cohort of United States Naval Surface Force officers

Study Objectives

This study analyzed fatigue and its management in US Naval Surface Force warships, focusing on understanding current practices and barriers, and examining the influence of organizational and individual factors on managing chronic fatigue. Furthermore, this study explored the impact of organizational and individual factors on fatigue management.

Methods

As part of a larger study, 154 naval officers (mean ± standard deviation; 31.5 ± 7.0 years; 8.8 ± 6.8 years of service; 125 male, and 29 female) completed a fatigue survey. The survey addressed (1) self-reported fatigue, (2) fatigue observed in others, (3) fatigue monitoring strategies, (4) fatigue mitigation strategies, and (5) barriers to fatigue mitigation. Logistic and ordinal regressions were performed to examine the effect of individual (i.e. sleep quality and years in military service) and organizational (i.e. ship-class) factors on fatigue outcomes.

Results

Fatigue was frequently experienced and observed by 23% and 54% of officers, respectively. Of note, officers often monitored fatigue reactively (i.e. 65% observed others nodding off and 55% observed behavioral impairments). Still, officers did not frequently implement fatigue mitigation strategies, citing few operationally feasible mitigation strategies (62.3%), being too busy (61.7%), and not having clear thresholds for action (48.7%). Fatigue management varies across organizational factors, which must be considered when further developing fatigue management strategies.

Conclusions

Fatigue remains a critical concern aboard surface force ships and it may be better addressed through development of objective sleep and fatigue monitoring tools that could inform leadership decision-making.

Time-of-day effects on speed and accuracy performance during simulated shiftwork

Performance on tasks involving speed and accuracy fluctuate throughout the 24-h day negatively affecting shift workers and organizations. Two simulated work shifts common in occupational settings were used to assess performance on a vigilance and math task. In study 1, 33 sleep-deprived participants completed a nightshift. In study 2, 32 partially sleep-deprived participants completed a dayshift. These studies found that performance differed between the type of task and the type of simulated shift where performance during the nightshift was worse than during the dayshift. In addition, collapsing speed and accuracy on the math task into inverse efficiency scores provided a unique measure that captured the impact of circadian rhythms during shiftwork. The current study also indicated that participants adopted cognitive strategies including speed-accuracy tradeoff and regulatory foci regarding work motivation (prevention focus and promotion focus) when completing the tasks depending on time-of-day, type of shift, circadian rhythms, and amount of sleep deprivation. This suggests that researchers and organizations should consider cognitive strategies in addition to the physiological components of sleep deprivation and circadian rhythms when investigating and documenting the impact of time-of-day due to different types of shiftwork conditions on performance and safety.

Prototyping Apps for the Management of Sleep, Fatigue, and Behavioral Health in Austere Far-Forward Environments: Development Study

BACKGROUND

Military service inherently includes frequent periods of high-stress training, operational tempo, and sustained deployments to austere far-forward environments. These occupational requirements can contribute to acute and chronic sleep disruption, fatigue, and behavioral health challenges related to acute and chronic stress and disruption of team dynamics. To date, there is no centralized mobile health platform that supports self- and supervised detection, monitoring, and management of sleep and behavioral health issues in garrison and during and after deployments.

OBJECTIVE

The objective of this study was to adapt a clinical decision support platform for use outside clinical settings, in garrison, and during field exercises by medics and soldiers to monitor and manage sleep and behavioral health in operational settings.

METHODS

To adapt an existing clinical decision support digital health platform, we first gathered system, content, and context-related requirements for a sleep and behavioral health management system from experts. Sleep and behavioral health assessments were then adapted for prospective digital data capture. Evidence-based and operationally relevant educational and interventional modules were formatted for digital delivery. These modules addressed the management and mitigation of sleep, circadian challenges, fatigue, stress responses, and team communication. Connectivity protocols were adapted to accommodate the absence of cellular or Wi-Fi access in deployed settings. The resulting apps were then tested in garrison and during 2 separate field exercises.

RESULTS

Based on identified requirements, 2 Android smartphone apps were adapted for self-monitoring and management for soldiers (Soldier app) and team supervision and intervention by medics (Medic app). A total of 246 soldiers, including 28 medics, received training on how to use the apps. Both apps function as expected under conditions of limited connectivity during field exercises. Areas for future technology enhancement were also identified.

CONCLUSIONS

We demonstrated the feasibility of adapting a clinical decision support platform into Android smartphone-based apps to collect, save, and synthesize sleep and behavioral health data, as well as share data using adaptive data transfer protocols when Wi-Fi or cellular data are unavailable. The AIRE (Autonomous Connectivity Independent System for Remote Environments) prototype offers a novel self-management and supervised tool to augment capabilities for prospective monitoring, detection, and intervention for emerging sleep, fatigue, and behavioral health issues that are common in military and nonmilitary high-tempo occupations (eg, submarines, long-haul flights, space stations, and oil rigs) where medical expertise is limited.

Who sleeps more and who works longer in the US Navy: Officers or enlisted personnel?

OBJECTIVES

To determine whether United States Navy (USN) officers and enlisted personnel have different sleep and work patterns while underway on USN surface ships.

METHODS

Variables of interest were assessed by actigraphy, activity logs, and validated questionnaires.

RESULTS

The 2 groups had similar daily sleep (officers: 6.41 ± 0.95 hrs/day; enlisted: 6.57 ± 0.97 hrs/day) and work duration. Enlisted personnel, however, were more likely to report excessive daytime sleepiness-EDS (41% more likely), clinically relevant insomnia (105%), to have both EDS and elevated insomnia (121%), to be classified as poor sleepers (17%), to use nicotine products (174%), and to forego routine exercise (57%). Enlisted personnel were 487% more likely to report all 3 of these behaviors: drink caffeinated beverages, use nicotine/tobacco products, forego routine exercise.

CONCLUSIONS

Even though the work and sleep hours do not differ significantly, the state of well-being of enlisted personnel is in general lower than officers. Our findings can provide insight to Navy leadership towards improving sailor well-being and crew endurance.

Measurement Methods of Fatigue, Sleepiness, and Sleep Behaviour Aboard Ships: A Systematic Review

Since seafarers are known to be exposed to numerous job-related stress factors that can cause fatigue, sleepiness, and disturbed sleep behaviour, the aim of this review was to provide an overview of the subjective and objective measurement methods of these strains. Using a systematic review, 166 studies were identified within the period of January 2010 to December 2020 using the PubMed database. Of the 21 studies selected, 13 used both subjective and objective measurement methods. Six studies used only subjective and two studies only objective methods. For subjective assessment, 12 different questionnaires could be identified as well as activity and sleeping logs. Actigraphy and reaction time tests (RTT) were the most common objective methods. In single cases, electrooculography (EOG), pupillometry and ambulatory polysomnography (PSG) were used. Measurement-related limitations due to vessel-related impacts were less often reported than expected. No restrictions of daily routines on board were described, and only single-measurement disturbances due to ship movements were mentioned. The present literature review reveals that there are various routines to measure fatigue, sleepiness, and sleep behaviour on board. A combination of subjective and objective methods often appears to be beneficial. The frequent use of actigraphy and RTT on board suggests good feasibility and reliable measurements with these methods. The use of ambulatory PSG in maritime-like contexts suggests that this method would also be feasible on board.

Self-reported sleep and sleep deficiency: Results from a large initiative of sailors attached to U.S. Navy warships

Chronic insufficient sleep is known to lead to a broad range of negative consequences (e.g. poor health and cognitive performance). While insufficient sleep and associated fatigue are present in many diverse populations, it is of special concern in high-risk military environments, where a mishap can result in catastrophic outcomes. Although many studies have been conducted to characterise sleep in general military populations, relatively few have been conducted using a large representative sample of sailors assigned to United States Naval warships. The present cross-sectional study characterises self-reported sleep parameters in sailors (N = 11,738) and explores the role of possible contributors to insufficient sleep. The results indicate that sailors, across a variety of different subgroups, do not obtain the amount of sleep that they report requiring for feeling well-rested. Of the many potential factors thwarting sleep, workload and an uncomfortable mattress are the most promising candidates to target for improvement.

The risk factors for insomnia and sleep-disordered breathing in military communities: A meta-analysis

BACKGROUND

Many reviews and meta-analyses had been conducted to investigate risk factors for sleep disorders in the general population. However, no similar research has been performed in the military population though insomnia and sleep-disordered breathing are quite prevalent in that population.

OBJECTIVES

To investigate risk factors for insomnia and sleep-disordered breathing in military personnel.

METHODS

A systematic literature search was performed from inception to March 2021 and 6496 records were produced. Two authors independently screened records for eligibility. Results were presented as odds ratios, and a random-effect model was used to pool results. Data analysis was performed respectively according to military personnel type (i.e., veteran, active-duty personnel). Risk factors were sorted into three categories: sociodemographic, army-specific, and comorbidity. This meta-analysis was registered in PROSPERO before data analysis (registration No: CRD42020221696).

RESULTS

Twenty-seven articles were finally included in the quantitative analysis. For sleep-disordered breathing in active-duty personnel, four sociodemographic (i.e., overweight/obesity, higher body mass index, male gender, >35 years old) and one comorbidity (i.e., depression) risk factors were identified. For insomnia in active-duty personnel, four sociodemographic (i.e., aging, alcohol dependence, white race, and female gender), two army-specific (i.e., deployment experience, combat experience), and four comorbidity (i.e., depression, post-traumatic stress disorder, traumatic brain injury, and anxiety) risk factors were identified. For insomnia in veterans, one army-specific (i.e., combat experience) and one comorbidity (i.e., post-traumatic stress disorder) risk factor was identified.

CONCLUSIONS

Several risk factors were identified for insomnia and sleep-disordered breathing in the current meta-analysis. Risk factors for veterans and active-duty personnel were partially different. Research on sleep breathing disorders remains limited, and more convincing evidence would be obtained with more relevant studies in the future.

Habitability in Berthing Compartments and Well-Being of Sailors Working on U.S. Navy Surface Ships

OBJECTIVE

The study had two objectives: (a) to assess the prevalence of sleep-related habitability concerns in the berthing compartments of U.S. Navy surface ships and (b) to assess whether habitability issues in berthing compartments affected the sleep and well-being of crew members.

BACKGROUND

The importance of habitability for human well-being is recognized. Little is known, however, about the association between habitability factors in the sleeping/berthing compartments and sailor well-being in operational conditions.

METHOD

Fit-for-duty sailors (N = 1,269; from six ships) participated in this naturalistic and longitudinal study. Sailors reported habitability factors affecting their sleep and completed four standardized questionnaires to assess daytime sleepiness, insomnia, sleep quality, and mood. Sleep was assessed through wrist-worn actigraphy and activity logs.

RESULTS

Noise, ambient temperature, poor bedding conditions, and ambient light were the most frequently reported factors of concern. Compared to their peers with fewer complaints, sailors with more habitability-related complaints were more likely to have elevated daytime sleepiness (by 23%) and to report insomnia symptoms (145%) and lower sleep quality (21%). Sailors who reported more habitability-related issues also tended to sleep longer. Individuals with more complaints about habitability also tended to report worse mood (total mood disturbance, tension/anxiety, depression, fatigue, and confusion/bewilderment).

CONCLUSION

Habitability-related complaints are associated with sailor well-being and sleep. Future studies should expound on the various detrimental factors that degrade conditions in berthing compartments and negatively impact crew well-being.

APPLICATION

Habitability in berthing compartments of surface ships is associated with sailors' daytime sleepiness, insomnia severity, mood, and sleep attributes. Ship designers should take these findings into consideration and investigate viable and cost-effective methods to mitigate the problems we identified.

The impact of shift work schedules on PVT performance in naturalistic settings: a systematic review

OBJECTIVE

The Psychomotor Vigilance Test (PVT) is considered the gold standard for detecting sleep loss and circadian misalignment related changes in performance in laboratory and field settings. This short 3-, 5- or 10-min test appraises an individual's sustained vigilant attention on a visual stimulus through reaction time, false starts and performance lapses. The PVT has been widely used as a measure to assess vigilant attention among shift workers, but information evaluating the application and performance of this test in different naturalistic shift work settings is limited. The purpose of this review is to synthesise and evaluate existing literature which has used the PVT to assess and monitor psychomotor performance in response to shift work schedules and rosters performed in real-world settings.

METHODS

A systematic search of studies examining PVT performance in response to 24/7 shift work schedules (e.g., day, afternoon, evening and night shifts) performed under naturalistic conditions was conducted. Articles were identified by searching Medline, Embase, CINHAL and PsycINFO databases in April 2020.

RESULTS

The search yielded 135 results, of which 16 publications were suitable to be included in this review. Articles were grouped according to when the PVT was applied to a research cohort, which included (a) multiple instances per shift, (b) commencement and cessation of shift and (c) other varying times.

CONCLUSIONS

This review suggests PVT performance is typically congruent across studies when the test is applied at generally consistent time intervals. The lack of research concerning the use of the PVT during extended duty shifts (e.g., shifts and on call work > 30 h) is an area for future research.

Comparison of Royal Canadian Navy Watchstanding Schedules

INTRODUCTION

Life on board a naval vessel is exceptionally demanding. Workdays for naval sailors can quite easily become 18+ hours long when watch schedules, training, and drills/evolutions are taken into account. Rotating watches and short off-watch periods can force sailors into a biphasic sleep pattern that is not sufficiently restful or a rotating pattern that is impossible to adapt to.

MATERIALS AND METHODS

Six different watch systems were evaluated over four separate at-sea trials. Engineering and tactical/combat departments have had different watch systems in the past because of constraints related to the specific environment in which they work. Therefore, two of the watch systems were engineering-specific watch evaluations, three of the systems were specific to tactical/combat departments, and one watch system was evaluated with the entire company of the naval vessel.

RESULTS

Both two-section (1-in-2) watch systems and three-section (1-in-3) watch systems were evaluated, which involve two or three shifts of sailors rotating through a full continuous 24-h day, respectively. Moving beyond three rotations of sailors is impossible on Canadian naval vessels due to bunk space and other limitations. The best watch system that we evaluated with respect to fatigue and quality of life at sea was the 1-in-3 straight 8-h shift system that was tested for the entire ships' company. The system has a single 8-h daily watch obligation (red watch, 4:00 am-12:00 pm; white watch 12:00 pm-8:00 pm; and blue watch, 8:00 pm-4:00 am). The best 1-in-2 system was the 8-4-4-8 system in which sailors are on-watch for 8 h, off-watch for 4 h, on-watch for 4 h, and then rest for 8 h. Both of these two systems have the advantage of equitably sharing the Window of Circadian Low (from about midnight to about 8:00 am), especially when melatonin concentration in the body is usually at its peak, between 2:00 am and 6:00 am.

CONCLUSIONS

The goal of this work was to comprehensively evaluate both submarine and surface fleet watch systems. We were able to develop alternative watch systems that increased Royal Canadian Navy operational readiness and improved the quality of life of our sailors at sea.

Analyzing the effect of social interaction on job demands and health in the example of flexible shiftwork

In the literature, shiftwork-related stress is often connected with health complaints. However, it has been shown that these are not equally distributed. Further reasons must exist as to why stress resulting from shiftwork only affects health in some cases. In a study with 653 employees working in highly flexible shiftwork conditions, an examination was made of the factors affecting the relationship between job demands and health status. The results show that satisfaction with leadership influences whether unevenly distributed work and time pressure have a significant impact on health. The factor of other people living in the household significantly influences whether time pressure and emotional stress lead to health complaints. The study concluded that the impact of social interaction as a resource is not limited to the workplace. Social interaction, as a personal resource, can be helpful in both the professional and private spheres.

Equation representing the dark-entrained transition from inaction to action in male and female mice

The activation of behaviour in a daily rhythm governed by the light cycle is a universal phenomenon among humans, laboratory mammals and other vertebrates. For mice, the active period is during the dark. We have quantified the increase in activity when the lights shut off (Light to Dark, L to D) using a generalized CNS arousal assay with 20 ms resolution, rather than traditional running wheels. Data analysis yielded the rare demonstration of an equation which precisely tracks this behavioural transition and, surprisingly, its reverse during D to L. This behavioural dynamic survives in constant darkness (experiment 2) and is hormone-sensitive (experiment 3). Finally (experiment 4), mice on a light schedule analogous to one which proved troublesome for U.S. Navy sailors, had dysregulated activity bursts which did not conform to the transitions between D and L. These experiments show the lawfulness of a behavioural phase transition and the consequence of deviating from that dynamic pattern. And, in a new way, they bring mathematics to the realm of behavioural neuroscience.

Sleep-Related Practices, Behaviors, and Sleep-Related Difficulties in Deployed Active-Duty Service Members Performing Security Duties

Objective: To assess sleep-related difficulties (e.g., trouble staying asleep, oversleeping, falling asleep while on duty, disturbing dreams, sleep paralysis) and behavioral patterns of active-duty service members (ADSMs) performing security duties. Participants: The participants were 1,169 ADSMs (20-44 years of age). Methods: ADSMs completed an online survey (67.3% response rate) with items assessing demographics, the occupational environment, sleep-related attributes, habits, or difficulties, factors affecting sleep, aids and techniques used to improve sleep, and the use of sleep-related products. Results: ADSMs reported sleeping ~6.5 hr/day (~56% reported sleeping < 6 hr). Sleep-related difficulties were reported by ~72% of the ADSMs (i.e., 55.1% had problems staying asleep, 33.1% reported experiencing sleep paralysis, 25.6% reported oversleeping, 21.6% had disturbing dreams, and 4.79% reported falling asleep while on duty). Daily sleep duration and quality, occupational factors (shift work, operational commitments, collateral duties, habitability, taking antimalarial medication, years deployed), and personal factors or behaviors (history of sleep problems, problems in personal life, late exercise times, altering sleep schedule to talk or text with family or friends) were associated with sleep-related difficulties. Some ADSMs reported using alcohol (~14%) or exercising prior to bedtime (~34%) in an attempt to fall sleep faster. Conclusions: We identified a high prevalence of sleep-related difficulties in our military sample. Even though most ADSMs used sleep hygiene practices to improve their sleep, some ADSMs used methods not recommended. Improving ADSMs' daily schedule (to include periods for exercising, and protected sleep periods), and further emphasis on sleep hygiene practices may be viable methods to reinforce behaviors promoting healthy sleep and improve performance.

Sleep in the United States Military

The military lifestyle often includes continuous operations whether in training or deployed environments. These stressful environments present unique challenges for service members attempting to achieve consolidated, restorative sleep. The significant mental and physical derangements caused by degraded metabolic, cardiovascular, skeletomuscular, and cognitive health often result from insufficient sleep and/or circadian misalignment. Insufficient sleep and resulting fatigue compromises personal safety, mission success, and even national security. In the long-term, chronic insufficient sleep and circadian rhythm disorders have been associated with other sleep disorders (e.g., insomnia, obstructive sleep apnea, and parasomnias). Other physiologic and psychologic diagnoses such as post-traumatic stress disorder, cardiovascular disease, and dementia have also been associated with chronic, insufficient sleep. Increased co-morbidity and mortality are compounded by traumatic brain injury resulting from blunt trauma, blast exposure, and highly physically demanding tasks under load. We present the current state of science in human and animal models specific to service members during- and post-military career. We focus on mission requirements of night shift work, sustained operations, and rapid re-entrainment to time zones. We then propose targeted pharmacological and non-pharmacological countermeasures to optimize performance that are mission- and symptom-specific. We recognize a critical gap in research involving service members, but provide tailored interventions for military health care providers based on the large body of research in health care and public service workers.

The complexity of human performance variability on watch standing task

The primary objective of this study was to examine the complexity of human temporal variability of topside roving watch task in naval operations concerning the reported times of ship status and to explore the potential presence of chaotic behavior and fractal properties of the reported log times. Topside rover reporting time intervals recorded in the deck logs of the USS Jason Dunham over the 2013-2015 period were analyzed to understand the underlying complexity of the watch standing task that is critical to the success of naval operations. The results on the 0-1 test, analysis of the largest Lyapunov exponents, as well the exploration of the fractal dimension and 1/f spectral analyses, showed that the fluctuation of standing watch time reports data exhibits chaotic and fractal system properties. The critical implications of the study findings for the human-centered design of complex systems were also discussed.

Improving Work and Rest Patterns of Military Personnel in Operational Settings with Frequent Unplanned Events

Members of the military get inadequate sleep due to a variety of reasons. Reduced manning, extended work hours, shiftwork schedules that result in circadian misalignment – all of these factors contribute to the sleep debt and degraded alertness observed in much of the military population. The issue of watchstanding schedules, performance, and alertness is of critical importance to the US military and is the focus of the current study. Based on a sample of active duty military members (N=75), this study had two goals. First, to conduct a field-based monitoring of the sleep and performance of military personnel while performing their duties. Second, to create and validate optimal recommendations based on the results of this empirical study. Participants wore actigraphs over a two-week period, completed daily activity logs, and took three-minute reaction time tests before and after standing watch on their regular schedules. Participants worked on a 2-day on/2-day off schedule, either in 3-section 8-hour shifts, or 2-section 12-hour shifts. Although there were no significant differences in the sleep amounts between the two schedules, results showed that participants on 8-hr shifts had fewer errors and less variable reaction time performance than those working 12-hr shifts. The 8-hr group reported better sleep quality, too. Our results suggest that the 8-hour schedule is better than the 12-hour schedule in terms of sleep and performance but may be more difficult to be applied. This study clearly shows the difficulty of implementing a specific watchstanding schedule in operational environments overloaded with unplanned, and irregular operational duties.

Discriminating Between Fatigue and Sleepiness in the Naval Operational Environment

OBJECTIVE

To assess the similarities and differences between reported levels of fatigue and sleepiness as a consequence of working at sea.

PARTICIPANTS

767 crewmembers of a U.S. Navy ship.

METHODS

Retrospective analysis of a survey to include questions about demographics, caffeine consumption, sleep adequacy, the Epworth Sleepiness Scale (ESS), and the Fatigue Severity Scale (FSS).

RESULTS

ESS scores (8.41 ± 4.66) indicated that 32% of the participants had excessive daytime sleepiness (ESS score > 10), while approximately 7% had an ESS score of 16 or more. FSS scores (average FSS = 3.01 ± 1.37) indicated that 28% of the participants had elevated fatigue (FSS score ≥ 4). Even though ESS and FSS scores were correlated (r = 0.39), their association explained only 15% of the variability observed. In terms of behavioral and lifestyle patterns, crewmembers with elevated fatigue (FSS ≥ 4) reported getting less exercise than those reporting less fatigue. Individuals with excessive sleepiness (ESS > 10) reported higher caffeine consumption. Crewmembers with elevated fatigue and comorbid sleepiness (FSS ≥ 4 and ESS > 10) reported receiving less sleep than other crew members.

CONCLUSIONS

These results suggest that subjective fatigue and subjective sleepiness, as measured by the FSS and ESS scales, are distinct constructs and both are consequences of working at sea. The scores on the two scales correlate differentially with behavioral and lifestyle patterns of the crewmembers.

Exploring Sleep-related Habitability Issues in Berthing Spaces on U.S. Navy Ships

Sleep problems are prevalent in the naval operational environment. Crewmembers attribute some of these problems to habitability-related issues in their berthing compartments. This study has two goals: first, to assess the provisions in current habitability standards used in ship design; and second, to assess the extent to which habitability factors in berthing compartments affect the sleep of crewmembers in United States Navy (USN) ships. Results from eight field studies show that environmental conditions (e.g., temperature, noise, light, air quality) affect sleep quality in berthing spaces. Despite the provisions in current standards, sleep-related habitability issues remain a concern for crewmembers in the USN. Our findings suggest that living conditions may be improved in berthing compartments by revising current standards. We have identified three areas for improvement: noise (both continuous and intermittent), temperature within the compartment, and designing berthing compartments according to the organizational structure of the ship.