The impact of returning to a daytime schedule on sleep, performance and mood after simulated fixed and rotating split shift schedules

Split shift schedules which minimise consecutive hours awake and maintain adequate total sleep time per 24h may be a suita-ble alternative to long shifts. However, when returning to a daytime schedule (RTDS), performance and sleep deficits may occur as a result of changing the timing of sleep and wake periods. The first aim of the current study was to check whether fixed and rotating split shift schedules with 20h time in bed (TIB) per 48h minimised cumulative deficits in sleep, performance and mood. The second aim was to investigate whether RTDS following these shift schedules had a negative impact on sleep, per-formance and mood. Twenty four participants (10M, 21-36y) completed a 9-day laboratory study with two 10h baseline sleeps (22:00h-08:00h); one of three shift conditions for four 24h periods: one of two 6h on / 6h off schedules, (Fixed A: 5h TIB at 03:00h/15:00h, or Fixed B: 5h TIB at 09:00h/21:00h), or an 8h on / 8h off schedule (Rotating: 6h40 TIB); and RTDS with 10h TIB for 2-nights (22:00h-08:00h). Psychomotor vigilance was stable throughout the shift schedule period. Subjective sleepi-ness (p<0.001), positive affect (p<0.01) and negative affect (p<0.001) were all significantly worse by the second 48h shift schedule period (SS2) compared to baseline (BL). Amount of Stage R sleep was significantly lower by SS2 compared to BL. Subjective sleepiness and positive affect returned to BL levels upon RTDS. Negative affect was significantly higher than BL upon RTDS (p<0.001). Stage R sleep was not significantly different to BL upon RTDS, however amount of N3 sleep upon RTDS was significantly reduced compared to BL in the Fixed B condition. For all conditions, sleep onset latency, N2 onset latency and N3 onset latency were significantly longer during RTDS compared to baseline (p<0.05). Consistent with previous litera-ture, split shift schedules did not result in cumulative impairments to sleep and performance. However, findings suggest that workers may still experience sleepiness and worsened mood. Switching back to a daytime schedule may also result in delays in falling asleep and also deep sleep