The sleep, circadian, and cognitive performance consequences of watchkeeping schedules in submariners: A scoping review.

Watchkeeping schedules are essential for maintaining submarine operations, but come with human risk factors including, disrupted sleep, circadian misalignment, and cognitive deficits. There is now an emerging literature examining the strengths and weaknesses of submarine watchkeeping schedules trialled in the field and under simulated laboratory conditions. The aim of this scoping review was to summarise this literature. A systematic search of peer-reviewed journal articles and industry reports listed in MEDLINE, PsychINFO, PubMed, Scopus, Embase and Google Scholar undertaken in May 2023 returned 7298 papers. Following screening procedures, 13 studies were identified for inclusion. The findings revealed that sleep was sufficiently preserved regardless of watchkeeping schedule (total sleep time = 5.46-7.89 h), circadian misalignment was greater for non-24 h schedules, and longer off-watch periods were associated with better cognitive performance. Taken together, when comparing between watchkeeping schedules, the present findings suggest that the 4 h-on/8 h-off and 8 h-on/16 h-off schedules may be a good compromise when balancing human risk factors and operational demands. However, submarines are complex and challenging environments to study and there is a need to expand the literature. More research comparing watchkeeping schedules is needed. Future studies should focus on cognitive performance measures, such as problem-solving, prioritisation and executive decision-making to address present shortcomings, and an examination of sleep and circadian countermeasures to assist with adaptation either initiated pre-deployment or by modifying the submarine environment itself should be considered.

The effect of time on task, sleep deprivation, and time of day on simulated driving performance.

Sleep deprivation and time of day have been shown to play a critical role in decreasing ability to sustain attention, such as when driving long distances. However, a gap in the literature exists regarding external factors, such as workload. One way to examine workload is via modulating time on task. This study investigated the combined effect of sleep deprivation, time of day, and time on task as a workload factor on driving performance. Twenty-one participants (18-34 years, 10 females) underwent 62 h of sleep deprivation within a controlled laboratory environment. Participants received an 8-h baseline and 9.5-h recovery sleep. Every 8 h, participants completed a Psychomotor Vigilance Task (PVT), Karolinska Sleepiness Scale (KSS), 30-min monotonous driving task and NASA-Task Load Index (TLX). Driving variables examined were lane deviation, number of crashes, speed deviation and time outside the safe zone. Workload was measured by comparing two 15-min loops of the driving track. A mixed model ANOVA revealed significant main effects of day and time of day on all driving performance measures (p < .001). There was a significant main effect of workload on lane deviation (p < .05), indicating that a longer time on task resulted in greater lane deviation. A significant main effect of day (p < .001) but not time of day for the NASA-TLX, PVT and KSS was found. Time on task has a significant further impact on driving performance and should be considered alongside sleep deprivation and time of day when implementing strategies for long-distance driving.