The purpose of this workplace evaluation was to assess the effects on performance,
alertness and subsequent sleep of strategic napping on 12-h overnight shifts. In a
counterbalanced crossover design, 24 male aircraft maintenance engineers working in a
forward rotating 12-h shift pattern volunteered to take part in the study for two work
weeks. During the experimental week, each subject was given the opportunity to take a
20-min nap at work between 01:00 and 03:00 h on each of their two overnight shifts. On
the control week no naps were taken on the night shifts. A computerized neurobehavioural
test battery was employed to assess performance and subjective levels of fatigue
at the beginning and end of each night shift, and pre- and postnap. Subjects were also
asked to rate how near they had come to falling asleep while driving to and from work.
The results revealed that taking a single 20-min nap during the first night shift
significantly improved speed of response on a vigilance task measured at the end of the
shift compared with the control condition. On the second night shift there was no effect
of the nap on performance. Taking a short nap during either night shift had no
significant effect on subjective ratings of fatigue, the level of sleepiness reported while
driving to and from work, or subsequent sleep duration and sleep quality. Overall the
results suggest some promise for a short duration nap taken in the workplace to
counteract performance deficits associated with the first night shift.