Investigation of the effectiveness of a split sleep schedule in sustaining sleep and maintaining performance

Abstract

Shift work is common in today’s society, and is associated with negative health outcomes, and accidents and incidents. These detrimental effects can be primarily attributed to sleeping and working at an adverse circadian time. The aim of this study was to examine whether a split sleep schedule is as effective as a consolidated day shift or night shift schedule for maintaining performance and sustaining sleep. Fifty-three healthy male volunteers (mean ± SD age = 26.51 ± 4.07 years) underwent a randomized three condition study design. A split sleep condition involving two 5-h sleeping opportunities in 24 h [time in bed (TIB) 0300 h–0800 h and 1500 h–2000 h] was compared to a 10-h consolidated nighttime sleep (TIB 2200 h–0800 h) and 10-h consolidated daytime sleep (TIB 1000 h–2000 h). All participants underwent a baseline period of 10 h of nocturnal time in bed (TIB) followed by a 5-d simulated workweek spent in one of the three conditions. Polysomnography, psychomotor vigilance task, digit-symbol substitution task and subjective state were assessed. During the 5-d simulated workweek, participants in the nighttime sleep condition slept the most (total sleep time per day (TST) 8.4 h ± 13.4 min), followed by the split sleep condition (TST 7.16 h ± 14.2 min) and the daytime sleep condition (TST 6.4 h ± 15.3 min). Subjective sleepiness was highest in the daytime sleep condition and lowest in the nighttime sleep condition. No significant differences in performance were observed between the conditions. Compared to a nighttime consolidated sleep opportunity or split sleep, placement of a consolidated sleep opportunity during the day yielded truncated sleep and increased sleepiness. Further research in real-world situations is warranted to fully assess the efficacy of alternative split sleep schedules for improving safety and productivity.

• Fatigue risk management
• scheduling
• shift work
• sleepiness
• split sleep
• vigilance

Acknowledgements

We thank the peer review committee of the project for their valuable comments and suggestions: Janet M. Mullington, PhD, Goran Kecklund, PhD, and Nancy J. Wesensten, PhD (Chair). We thank Hans P.A. Van Dongen, PhD, for help with study design and for making available data and experimental materials of the study “Duration of Restart Period Needed to Recycle with Optimal Performance: Phase II” from which the data for the daytime sleep condition in this study were drawn. We also wish to thank the staff and students at Sleep and Performance Research Center, Washington State University, Spokane who assisted with data collection.