J. Axelsson et al., Effects of alternating 8- and 12-hour shifts on sleep, sleepiness, physical effort and performance, SC J WORK E, 24, 1998, pp. 62-68
Objectives The aim of the present study was to compare 12-hour shifts durin
g weekends with 8-hour shifts during weekdays with respect to sleep, sleepi
ness, physical effort, and performance.
Methods Thirty-one subjects at a power plant participated. Sleep, sleepines
s, and physical effort were measured with a diary. About half of the subjec
ts carried out a reaction-time test during both 8- and 12-hour morning and
night shifts. The remaining subjects carried out a vigilance task.
Results sleepiness was higher and physical effort lower on the 12-hour nigh
t shift than on the 8-hour night shift. However, the subjects who had the s
ame level of physical effort on 8- and 12-hour night shifts did not differ
with respect to sleepiness. During the 12-hour morning shift, sleepiness wa
s lower and the sleep length was longer than on the 8-h morning shift. The
subjects who had the same amount of sleep for 8- and 12-hour morning shifts
showed no difference in sleepiness. sleep did not differ between 8- and 12
-hour night shifts. There was no difference between 8- and 12-hour shifts w
ith respect to performance.
Conclusions It was suggested that the difference in sleepiness between 8- a
nd 12-hour shifts is related to differences in sleep length for the morning
shift, and to differences in physical effort for the night shift, rather t
han to shift duration. Thus the most likely conclusion is that 12-hour shif
ts do not cause increased sleepiness or impaired performance or disturbed s
leep.