DELAYING AND EXTENDING SLEEP DURING WEEKENDS - SLEEP RECOVERY OR CIRCADIAN EFFECT

There is a well-known tendency to delay and prolong our sleep during w eekends (Saturday and Sunday), with an advance and reduction of sleep during workdays (Monday to Friday). The objective of this work was to determine if the changes of sleep during weekends are produced by a pa rtial sleep deprivation or a lack of entraining of circadian rhythms t o an advanced phase, during workdays. The subjects were 52 undergradua te female students, mean age = 17.5 years, SD = 1.32. All students att ended school following a regular schedule, from Monday to Friday. Two groups of students were studied: one attended school from 07:00 to 12: 00 h (morning group, n = 30); the other attended school from 14:00 to 18:00 (afternoon group, n = 22). None of the students worked or was en gaged in other activity with a fixed schedule. All kept a sleep-wake d iary for 2 weeks, in which they recorded their bedtimes, wakeup times, and sleep-onset latencies. The morning group delayed 47.4 min [t(29) = 4.72, p < 0.0001] and prolonged their sleep 118.2 min [t(29) = 9.4, p < 0.0001] during weekends. Although the afternoon group had the oppo rtunity to maintain a delayed phase and a long sleep time throughout t he week, they delayed their bedtime by 24 min [t(21) = 2.99, p < 0.01] during weekends, without changing their sleep duration. The findings suggest that the prolonged sleep during weekends is due to reduction o f sleep during workdays, whereas the delay of bedtime seems to be asso ciated with a tendency of the human circadian system to maintain a del ayed phase with respect to the solar daylight period.