When the human circadian system is caught napping: evidence for endogenous rhythms close to 24 hours

Sleep. 1993 Oct;16(7):638-40.


It is now well acknowledged that napping constitutes an inherent component of the human circadian system. To date, however, few studies have examined the effects of spontaneous napping on human free-running rhythms. This study investigated the free-running circadian periods of rest/activity and body core temperature in a group of young subjects who were permitted to nap during their time in isolation. Based on the frequency of self-reported sleep bouts, subjects were classified as Nappers or Nonnappers. Nappers exhibited free-running rhythms in both rest/activity and body core temperature that were not significantly different from 24 hours. Nappers showed a tendency for shorter free-running periods in both variables, when compared with Nonnappers. These findings emphasize the need for careful reassessment of data obtained from traditional free-run protocols.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Circadian Rhythm / physiology*
  • Female
  • Humans
  • Male
  • Sleep / physiology*