Effect of Day Length on Sleep Habits and Subjective On-Duty Alertness in Irregular Work Schedules

Abstract

The human circadian system is sensitive to environmental conditions, such as those created by shift work, that affect the timing and duration of sleep. Previous research on the effects of shift work, however, has focused primarily on regularly scheduled shifts. Few studies have focused on irregular and unpredictable on-call shift systems, such as those found in much of railroad operations. The purpose of the current study was to examine the effect of irregular shift systems experienced by locomotive engineers on the length of sleep-wake periods and the effect of different length sleep-wake periods on self-reported sleep quantity, sleep quality, and on-duty alertness. A total of 179 locomotive engineers provided information on work times, sleep habits, and on-duty alertness as part of a 14-day activity log. Sleep-wake periods were first divided into three categories: short (<22 h), normal (22 to 26 h, inclusive), and long (>26 h). A one-way analysis of variance for multiple variables was completed on sleep quantity, sleep quality, and on-duty alertness by using the three sleep-wake period categories as the factor. The results indicated that normal-length periods occurred in less than half of the sleep-wake periods. The remaining sleep-wake periods were divided approximately equally between short and long periods. In addition, short sleep-wake periods resulted in less sleep and generally poorer sleep than normal length sleep-wake periods. Long sleep-wake periods resulted in more sleep but poorer sleep and lower levels of on-duty alertness than normal sleep-wake periods. Furthermore, on-duty alertness followed a circadian rhythm with the most well defined rhythm seen in normal length sleep-wake periods and less pronounced rhythms seen in short and long sleep-wake periods. The current data indicated that the range of sleep-wake periods caused by irregular working conditions negatively impacted sleep habits and on-duty alertness in locomotive engineers.