Improving sailor's amount and efficiency of sleep in two-section watchkeeping schedules: A cluster randomized trial...

The present study aimed at comparing sailors' amount and efficiency of sleep in two two-section watchkeeping schedules, i.e. the traditional 6/6 and the 7-5-5-7. Intention for the latter schedule was to align the major sleep episodes with biologically driven nocturnal sleep patterns.

Using a parallel crossover design with cluster randomized trials, forty-eight crew members from two vessels of the German Navy participated in a field trial with two 1-week underway periods varying the watchkeeping schedule in randomized order. Sleep minutes and sleep efficiency were assessed on the participant level using wrist-worn actigraphs and analyzed for sleep episodes occurring during the day (i.e. between 10:00 am and 10:00 pm) and during the night (i.e. between 10:00 pm and 10:00 am).

Nighttime sleep duration was 14 min longer and with 10% higher sleep efficiency in the 7-5-5-7 schedule compared to the 6/6. In contrast, daytime sleep duration was 40 min longer in the 6/6 with no statistically significant differences in sleep efficiency between the two watchkeeping schedules.

Our results suggest that the amount and efficiency of nighttime sleep can be enhanced with the 7-5-5-7. Hence, even in shift schedules with restricted periods for rest, recuperation can be improved by more closely aligning watchkeeping schedules to the innate human diurnal circadian cycles. Statement of Significance The size of ships and the associated limitations on the size of their crews make two-section watchkeeping schedules common in civil and military maritime settings. Such watchkeeping schedules-in which the 24-h day must be shared between two watches-limit time available for rest and recuperation. The present study shows that even in this context, slight modifications in two-section watchkeeping schedules lead to more and better nighttime sleep because the circadian fluctuations of sleep and performance are considered. Our research findings have high practical significance for all industries with shift workers and demonstrate how the negative effects of watchkeeping schedules can be reduced if they are adapted to better align with innate human circadian rhythms.