Factors Affecting the Recuperative Value of Naps

The extent to which naps will be beneficial, in terms of improved self-perceived alertness, performance, and objective alertness, is likely to depend on a number of factors. The factors of particular significance that will be addressed in this chapter include (a) sleep inertia, (b) nap duration, (c) nap sleep infrastructure, (d) circadian timing, (e) prior wake time, (f) napping strategies for periods of extended wakefulness, (g) individual differences, and (h) the setting (laboratory vs. applied settings). The discussion will now turn to the first of these factors, sleep inertia. 

Sleep inertia, the experience of inferior task performance and/or disorientation occurring immediately after awakening from sleep (10, p. 226), is a well-documented consequence of napping (11). Although sleep inertia is said to dissipate 

To summarize, sleep inertia is a factor to consider when implementing a napping strategy. As sleep inertia appears to be affected by the duration of slow-wave sleep within the sleep period and slow-wave sleep occurring at arousal, sleep inertia tends to accompany naps in excess of 20-30 min. For this reason, as well as the fact that naps greater than 20 min appear to produce characteristically different postnap effects compared to naps of shorter duration, naps in excess of 20 min duration will henceforth be referred to as long naps and those 20 min and shorter will be termed brief naps. 

Notwithstanding the initial effects of sleep inertia that may accompany long naps, they have been shown to produce beneficial effects after normal nocturnal sleep (26-29), sleep restriction (30), total sleep deprivation (31), as well as during experimental night shifts (32,33) and periods of sustained wakefulness (1). Reported benefits include increased post-nap sleep latency (30,31,33), improved 

However, as an additional factor to consider, the benefits of long naps may be tempered by the fact that they may disrupt the duration and architecture of the subsequent sleep period (3,34). In this capacity, long naps may lead to further sleep loss (15). Brief naps, on the other hand, do not appear to affect subsequent sleep duration and quality (35). 

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