Impact of nap length, nap timing and sleep quality on sustaining early morning performance.

The study examined how nap length, nap timing and sleep quality affect early morning performance (6:00 to 8:00). Twelve students participated in a simulated nightshift schedule (22:00 to 8:00) where the length and timing of nocturnal naps were manipulated (0:00-1:00, 0:00-2:00, 4:00-5:00 and 4:00-6:00). A performance test battery was administered consisting of a psychomotor vigilance test, a logical reasoning test, and a visual analogue scale for subjective fatigue and sleepiness. The results showed that a 120-min nap sustained early morning performance better than a 60-min nap. Taking a nap earlier or later did not affect the neurobehavioral performance tests, although participants slept more efficiently during naps later in the night shift. A negative effect of a nocturnal nap during the night shift on subsequent daytime and nocturnal sleep was not observed in the sleep architecture. It still remains unclear whether slow wave sleep plays an important role in sustaining early morning performance. In terms of work safety and sleep health, the results suggest that a longer and later nap is beneficial during night shifts.