Work activity during night shifts:: A review of 25 years of research and perspectives

This paper proposes a review of shift work research based on work analysis. Most studies on this topic have been conducted in the fields of ergonomics, psychophysiology, or chronobiology. First, we recall the impact of shift-work on the human organism, while taking into account the normal circadian rhythm of the body's psychophysiological functions. Shift-workers and especially night workers have difficulty maintaining a high level of alertness at work, due to both a circadian decrease in the middle of the night and an accumulation of wakefulness during the night shift. This phenomenon is manifested during night shifts by a performance decline in various work situations. In most cases, though, shift-workers manage to accomplish their tasks in a satisfactory way. Consequently, a simple study of "performance" is insufficient for understanding work strategies and the true work load. We then take a more in depth look at the specificities of shift work. Hourly variations in activity have been found in some ergonomic studies. Operators perform their tasks in a different way according to both the type of shift and the work hours. A few studies have stressed that shift workers use a different work strategy at night than in the morning or afternoon. In the same way, hour-dependent fluctuations in work activity are observed during night shifts. Thus, shift workers adapt their work strategies to their physiopsychological capacities as well as to the task demands. Finally, the means of compensating for difficulties related to night work are discussed A decrease in alertness during night shifts can be managed on least two levels. Firstly, taking regular night naps can have number of benefits for operators and their reliability. Secondly, some results have revealed that the cooperative aspects of work can mask individual rhythmicities and can provide a way for operators to cope with decreases in alertness. These findings underline the importance of cooperative activity in managing individual chronobiological constraints, particularly by specific mutual aids or task transference.