A polysomnographic study of morning and afternoon sleep quality during simulated night shift work.

Shiftworkers differ as to scheduling their day sleep between night shifts. An experimental study was carried out to compare the effects of morning and afternoon sleep behaviour on sleep quality within and after a period of seven night shifts. Twelve young males participated in a repeated-measures design, six sleeping in the morning and six in the afternoon after night shifts. Sleep quality was evaluated by polysomnographic and subjective measures. Morning and afternoon sleepers showed some differences in the trend of sleep changes over successive sleep periods. However, at the end of the night shift week, there were no marked differences in sleep quality. Both morning and afternoon sleep were characterized by deep sleep, and short sleep onset latencies.