Effects of physical positions on sleep architectures and post-nap functions among habitual nappers.

The post-lunch sleepiness is considered to be part of biological rhythm. Many people take nap as a countermeasure to this afternoon circadian nadir. The aim of the study is to investigate the effect of a short-term midday nap in different physical positions after a full night sleep on subjective and physiological measures. Thirty-six young healthy habitual nappers (18 men, 18 women) aged 18-23 participated in the study. They were randomly assigned to three experimental conditions: to nap in a seat (NS), to nap in a bed (NB) and no-nap (NN). Measures of subjective sleepiness, mood, fatigue, and P300 component were taken before and after a 20min nap. Results showed that sleepiness, fatigue, and mood for both NS and NB were improved after napping. Moreover, objective alertness was enhanced in NB relative to NS and NN, which showed the larger P300 amplitude after nap. The delta power during sleep stage 2 of NS was inferior to that of NB, which induced a lower alertness after the sitting nap. Consequently, the result demonstrated the function of delta wave during stage 2 on arousal level following the brief midday nap. In general, taking a nap in a seat is a way to subjective restoration but taking a nap in a bed benefits the habitual nappers subjectively and physiologically.