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

Abstract

We assessed sleep patterns, psychomotor vigilance performance, work demands and mood of 77 crewmembers of USS NIMITZ (CVN-68) on the rotating 5-h on/10-h off (5/10) watchstanding schedule. Within the 3-day cycle of the 5/10, sleep occurred at distinctly different times each day. On two of these days, sailors typically received only brief, 4-h sleep episodes followed by periods of sustained wakefulness (approximately 22 and 20 h). Crewmembers received approximately seven hours of sleep daily, but reported excessive fatigue and dissatisfaction with their schedule. Crewmembers' mood worsened significantly over the course of the underway phase. Psychomotor vigilance performance (reaction times, lapses) was significantly degraded compared to performance when working circadian-aligned schedules. Overall, standing watch on the 5/10 schedule, combined with other work duties, resulted in poor sleep hygiene. Crewmembers on the 5/10 experienced periodic bouts of sustained wakefulness and accrued a significant sleep debt due to extended workdays and circadian-misaligned sleep. Practitioner summary:We assessed crewmembers' sleep patterns, psychomotor vigilance performance and work demands when working a rotating 5-h on/10-h off (5/10) watchstanding schedule. The 5/10, combined with other work duties, resulted in poor sleep hygiene. Crewmembers experienced periodic bouts of sustained wakefulness and accrued a significant sleep debt due to extended workdays and circadian-misaligned sleep.

Sleep in the United States Military

“…At this ontogenetic time, sleep/wake cycles are still transitioning to adult patterns [11]. This runs counter to the sleep/wake schedules of military training to which these adolescents enter, where <6 h of sleep per night and rise times of 04:30 are commonplace [17–20]. Unfortunately, insufficient sleep <6 h per night becomes chronic and normative during early training and is pervasive even at elite military academies [17, 19].…”

“…One military population that is more conducive to short-term studies of shift work is the Navy, where Sailors are deployed on ships for days to weeks at a time and tend to have more defined watch duties while at sea. Researchers located at the Naval Postgraduate School have published a number of studies that leveraged this population, with particular emphasis on deriving watch schedules that better align with circadian rhythms [34] and offer more time for dedicated sleep [35] than the common rotating 5 h on/10 h off watch schedule [20]. These studies consistently suggest that Sailors prefer the 3 h on/ 9 h off watch schedule, with less reported daytime sleepiness and improved mood and reaction times with fewer errors.…”

Discriminating Between Fatigue and Sleepiness in the Naval Operational Environment

“…This chronic situation may lead to elevated daytime sleepiness which, in turn, can lead to greater caffeine consumption. Even though studies in controlled conditions have showed that caffeine consumption may lead to sleep disruption (Karacan et al, 1976), we believe that the major explanation for sleep deprivation in the naval environment is the restricted opportunities to sleep at circadianappropriate times (Shattuck & Matsangas, 2015c). Previous research has demonstrated that crew members working on circadian-based watch schedules receive better sleep, feel more alert, and their caffeine consumption is reduced (Shattuck, Matsangas, & Brown, 2015).…”

“…The effect of restricted sleep at sea is further magnified by the poor quality of sleep that most crew members get, primarily for two reasons. First, they are working in shifts; therefore, they sleep at irregular times (Shattuck & Matsangas, 2015c). Second, crew members sleep in berthing compartments in which environmental noise (other crew members in the same compartment, external noises, etc.)…”

An update on stress, fatigue and wellbeing: implications for naval personnel

“…Again, research has either focused on specific roles (e.g. naval aviators [25]; commanding officers [26], watch-keepers [27,28] or a range of crew members [29]) often in operational settings [30,31] but sometimes in non-operational settings as well [32].…”