Effect of a relatively long afternoon nap on autonomous nervous activity, sleep architecture, and subjective sleep quality

Abstract

Post‐lunch sleepiness and deterioration in performance, or ‘post‐lunch dip’, is considered a part of the biological rhythm. A short nap is a promising countermeasure to the post‐lunch dip. Compared to the extensive studies on the effects of a short nap, there is limited research on the physiological impact of a relatively long nap such as 60 min or more in the afternoon. Forty‐three male university students with normal sleep–wake cycles were assigned to two groups: group 1 slept for 6 h from 0:00 to 6:00, and group 2 napped for 2 h from 13:15 to 15:15. There was no prominent difference in the subjective quality of sleep between the groups. This was supported by the lack of any significant difference in sleep efficiency and latency between the groups. Additionally, the heart rate after the afternoon nap was significantly higher than the baseline level before nap (overshoot), whereas the heart rate in the morning was the same as recorded the night before. The relatively long afternoon nap may be comparable with a night's sleep in terms of sleep quality, whereas it may enhance greater autonomic arousal after awakening than that in the morning. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.