The use of a short (< 1 h) nap in improving alertness during the early morn
ing hours in the first night shift was examined under laboratory conditions
. The study contained four experimental, non-consecutive night shifts with
a nap of either 50 or 30 min at 01.00 or 04.00 hours. An experimental night
shift without a nap served as a control condition. Each experimental shift
was followed by daytime sleep. Fourteen experienced male shift workers wen
t through all of the experimental conditions. The results showed that the n
aps improved the ability eo respond to visual signals during the second hal
f of the night shift. Physiological sleepiness was alleviated by the early
naps, as measured 50 min after awakening, but not at the end of the shift.
Subjective sleepiness was somewhat decreased by the naps. The naps produced
sleep inertia which lasted for about 10 15 min. Daytime sleep was somewhat
impaired by the 50 min naps. The study shows that a nap shorter than I h i
s able to improve alertness to a certain extent during the first night shif
t.