title: The efficacy of a restart break for recycling with optimal performance depends critically on circadian timing.
abstract: OBJECTIVE
  Under simulated shift-work conditions, we investigated the efficacy of a restart break for maintaining neurobehavioral functioning across consecutive duty cycles, as a function of the circadian timing of the duty periods.
  
  
  METHODS
  As part of a 14-day experiment, subjects underwent two cycles of five simulated daytime or nighttime duty days, separated by a 34-hour restart break. Cognitive functioning and high-fidelity driving simulator performance were tested 4 times per day during the two duty cycles. Lapses on a psychomotor vigilance test (PVT) served as the primary outcome variable. Selected sleep periods were recorded polysomnographically.
  
  
  METHODS
  The experiment was conducted under standardized, controlled laboratory conditions with continuous monitoring.
  
  
  METHODS
  Twenty-seven healthy adults (13 men, 14 women; aged 22-39 years) participated in the study.
  
  
  METHODS
  Subjects were randomly assigned to a nighttime duty (experimental) condition or a daytime duty (control) condition. The efficacy of the 34-hour restart break for maintaining neurobehavioral functioning from the pre-restart duty cycle to the post-restart duty cycle was compared between these two conditions.
  
  
  RESULTS
  Relative to the daytime duty condition, the nighttime duty condition was associated with reduced amounts of sleep, whereas sleep latencies were shortened and slow-wave sleep appeared to be conserved. Neurobehavioral performance measures ranging from lapses of attention on the PVT to calculated fuel consumption on the driving simulators remained optimal across time of day in the daytime duty schedule, but degraded across time of night in the nighttime duty schedule. The 34-hour restart break was efficacious for maintaining PVT performance and other objective neurobehavioral functioning profiles from one duty cycle to the next in the daytime duty condition, but not in the nighttime duty condition. Subjective sleepiness did not reliably track objective neurobehavioral deficits.
  
  
  CONCLUSIONS
  The 34-hour restart break was adequate for maintaining performance in the case of optimal circadian placement of sleep and duty periods (control condition) but was inadequate (and perhaps even detrimental) for maintaining performance in a simulated nighttime duty schedule (experimental condition). Current US transportation hours-of-service regulations mandate time off duty but do not consider the circadian aspects of shift scheduling. Reinforcing a recent trend of applying sleep science to inform policymaking for duty and rest times, our findings indicate that restart provisions in hours-of-service regulations could be improved by taking the circadian timing of the duty schedules into account.
authors: Sleep and Performance Research Center, Washington State University Spokane, PO Box 1495, Spokane, WA 99210-1495, USA. hvd@wsu.edu
authors: Hans P A
authors: HP
authors: Van Dongen
authors: Gregory
authors: G
authors: Belenky
authors: Bryan J
authors: BJ
authors: Vila
mesh_terms: D000328:Adult; D003071:Cognition; D003072:Cognition Disorders / Q000209:etiology; D005260:Female; D006801:Humans; D008297:Male; D017286:Polysomnography; D011640:Public Policy; D012890:Sleep / Q000502:physiology; D012892:Sleep Deprivation; D020178:Sleep Disorders, Circadian Rhythm / Q000503:physiopathology*; D013647:Task Performance and Analysis; D014186:Transportation; D014940:Work Schedule Tolerance; D055815:Young Adult