Recuperative Power of a Short Daytime Nap With or Without Stage 2 Sleep

STUDY OBJECTIVESThe recuperative effect of a nap of less than 30 minutes has been confirmed. Such naps consist mainly of stages 1 and 2 sleep. The present study examined whether sleep stage 1 or 2 contributed to the recuperative effect of a short nap.DESIGNRepeated-measurement within-subject design. After sleep was restricted to 1.5 hours less than their usual nocturnal sleep, participants took a rest (No-nap condition) or a nap at 2:00 PM. In the nap condition, they were awakened after 5 minutes of stage 1 sleep (S1-nap condition) or 3 minutes after stage 2 sleep appeared (S2-nap condition).SETTINGUniversity sleep laboratory.PARTICIPANTSTen healthy university students (aged 19 to 24 years).MEASUREMENTSSubjective mood, performance on visual detection and symbol-digit substitution tasks, and the number of slow eye movements during a performance task were measured before and after the nap or rest.RESULTSIn the No-nap condition, subjective mood and performance deteriorated, and Slow eye movements increased during mid-afternoon, suggesting that the post-lunch dip occurred. In contrast, subjective alertness and performance improved and slow eye movements rarely occurred in the S2-nap condition. Although subjective sleepiness and fatigue improved, performance deteriorated and slow eye movements increased in the S1-nap condition.CONCLUSIONA daytime short nap containing 3 minutes of stage 2 sleep has recuperative effects, whereas these effects are limited following only stage 1 sleep.