0284 The Effects of a Circadian-Aligned Watchbill Shift Work Schedule on Sleep Quality and Quantity in U.S. Navy Submarine Personnel

Introduction Prior to 2014, the U.S. Navy Submarine Force operated on a non-circadian-aligned watchbill shift work schedule (18-hour day-length) that resulted in insufficient sleep. For instance, prior research reported that submariners received insufficient sleep on this schedule, and modest sleep restrictions can adversely affect performance, alertness, and, ultimately, negatively impact mission outcomes. Thus, the present study characterized sleep patterns of submariners operating on a newer, circadian-aligned 24-hour day-length watchbill. Methods Submariners (n=58; 27.8±5.9 years) of various ranks volunteered from a U.S. Navy submarine. Submariners wore a research-grade actigraphy watch over a 30-day underway mission, for objective sleep measurement of time in bed (TIB), total sleep time (TST), and sleep efficiency (SE). Subjective sleep was measured from questionnaires (Pittsburgh Sleep Quality Index [PSQI], Insomnia Severity Index [ISI], Profile of Mood States [POMS-fatigue subscale]) that were taken pre- and post-underway. Results Compared with pre-underway, at post-underway submariners reported significantly higher scores on the ISI, PSQI global sleep quality, and POMS-fatigue (all p<0.05, indicating worse sleep and fatigue ratings). According to actigraphy, submariners acquired on average 6.7±1.0 hours TST, 7.5±1.1 hours TIB, and 88.9±3.9 % SE per day throughout the underway mission. Actigraphy-determined TIB and TST were variable compared with PSQI self-reported TIB and TST. Conclusion Study results indicate that submariners experience modest sleep restriction on a newly implemented 24-hour watchbill, which is an improvement in sleep relative to prior assessments of the former standard 18-hour watchbill. However, submariners endorsed lower sleep quality and higher fatigue levels from a month-long underway mission. This study is one of the first examinations of sleep under the 24-hour watchbill mandate that was instated in 2014. Future studies should further evaluate sleep and test fatigue mitigation strategies in different shift configurations of the 24-hour watchbill. Support Joint Program Committee-5 Fatigue Mechanisms and Countermeasures Working Group