The influence of split sleep-wake schedules and daytime sleep strategies on neurobehavioural performance

Introduction: Consumer demands for 24‐h services have led to an increase in employees engaged in shiftwork. However, since these schedules often restrict sleep to biologically inopportune times, the risk of fatigue‐related accidents is a significant concern. As such, two studies were conducted to evaluate alternative sleep‐scheduling options that might optimise performance in situations where long nocturnal sleep episodes are not feasible. Methods: Study 1 considered the effectiveness of short sleep‐wake cycles at sustaining performance around the clock. Twenty‐nine males participated in a 13‐day, 28 h forced desynchrony (FD) protocol in one of two conditions. All obtained the same total time in bed, allocated as one 9.3 h episode per 28 h in the “standard sleep” condition or 4.7 h per 14 h in the “split sleep” condition. Circadian time was estimated from body temperature. Study 2 assessed different daytime sleep strategies between two simulated 12‐h night shifts. Twelve males each participated in three conditions, which differed only in the timing of sleep. The strategies included an immediate sleep, a delayed sleep, and two short sleeps. Performance in both studies was assessed regularly in terms of lapses on the PVT. Results: For the first study, mixed‐models ANOVAs revealed no overall difference between consolidated and split schedules [F(1,30)=2.20, p > .05]. However, there was a significant interaction between schedules and circadian phase such that fewer response lapses occurred at night in the split schedule than the consolidated schedule [F(5,795)=3.8, p > .05]. For Study 2, repeated measures ANOVA showed no differences between the three sleep strategies in night‐time mean lapse count [F(2,183)=0.79, p > .05]. Discussion: The results from both studies indicate that splitting sleep episodes is not inherently harmful to performance provided the total duration is sufficient. Study 1 suggests split work‐rest schedules may be preferable to traditional night shifts for sustaining performance in some industries. Study 2 suggests the timing and arrangement of daytime sleep between long 12 h nights shifts is not critical for nocturnal function.