A Brief Afternoon Nap Following Nocturnal Sleep Restriction: Which Nap Duration is Most Recuperative?

STUDY OBJECTIVES: The purposes of this study were to compare the benefits of different length naps relative to no nap and to analyze the electroencephalographic elements that may account for the benefits. DESIGN: A repeated-measures design included 5 experimental conditions: a no-nap control and naps of precisely 5, 10, 20, and 30 minutes of sleep. SETTING: Nocturnal sleep restricted to about 5 hours in participants' homes was followed by afternoon naps at 3:00 PM and 3 hours of postnap testing conducted in a controlled laboratory environment. PARTICIPANTS: Twenty-four healthy, young adults who were good sleepers and not regular nappers. MEASUREMENTS AND RESULTS: The 5-minute nap produced few benefits in comparison with the no-nap control. The 10-minute nap produced immediate improvements in all outcome measures (including sleep latency, subjective sleepiness, fatigue, vigor, and cognitive performance), with some of these benefits maintained for as long as 155 minutes. The 20-minute nap was associated with improvements emerging 35 minutes after napping and lasting up to 125 minutes after napping. The 30-minute nap produced a period of impaired alertness and performance immediately after napping, indicative of sleep inertia, followed by improvements lasting up to 155 minutes after the nap. CONCLUSIONS: These findings suggest that the 10-minute nap was overall the most effective afternoon nap duration of the nap lengths examined in this study. The implications from these results also suggest a need to consider a process occurring in the first 10 minutes of sleep that may account for the benefits associated with brief naps.