Guiding principles for determining work shift duration and addressing the effects of work shift duration on performance, safety, and health: guidance from the American Academy of Sleep Medicine and the Sleep Research Society

Abstract

Risks associated with fatigue that accumulates during work shifts have historically been managed through working time arrangements that specify fixed maximum durations of work shifts and minimum durations of time off. By themselves, such arrangements are not sufficient to curb risks to performance, safety, and health caused by misalignment between work schedules and the biological regulation of waking alertness and sleep. Science-based approaches for determining shift duration and mitigating associated risks, while addressing operational needs, require: (1) a recognition of the factors contributing to fatigue and fatigue-related risks; (2) an understanding of evidence-based countermeasures that may reduce fatigue and/or fatigue-related risks; and (3) an informed approach to selecting workplace-specific strategies for managing work hours. We propose a series of guiding principles to assist stakeholders with designing a shift duration decision-making process that effectively balances the need to meet operational demands with the need to manage fatigue-related risks.

Keywords: alertness; circadian rhythms; mental fatigue; occupational medicine; policy making; productivity; shift scheduling; sleep homeostasis; sleepiness; working time arrangements.

Figure 1. Factors influencing the performance, safety and health risks associated with shift duration.

This diagram illustrates the multiple factors to be considered in balancing the needs of an operational setting, the human resource requirements to meet those needs, and the pivotal and complex role of shift duration. Shift duration competes with other demands on people’s time—for example, for commuting, eating, personal hygiene, non-work-related commitments, and social activities—and restricts the time available for sleep.^,, Fatigue/sleepiness associated with reduced and displaced sleep and with the timing of the biological clock (circadian rhythm), in conjunction with individual traits (e.g. vulnerability to sleep loss) and workplace characteristics and hazards determines overall risk levels.^, Evaluation of these interconnected factors is pertinent to decision making about shift duration.

Figure A1. Regulation of sleepiness by two biological processes.

A circadian process (red) produces a rising pressure for wakefulness, which counteracts fatigue, during the day; and a withdrawal of that pressure for wakefulness, thereby promoting sleepiness, during the night. Simultaneously, a homeostatic process (blue) builds up a pressure for sleep, thereby promoting sleepiness, during periods of wakefulness; and dissipated that pressure for sleep (dark gray), thereby providing recovery, during periods of sleep (top panels). The combined effect of the circadian and homeostatic processes on sleepiness may be calculated as the net difference between the homeostatic pressure for sleep and the circadian pressure for wakefulness (bottom panels, green), as illustrated here for a scenario with a daytime duty period (light blue) and an 8-h nighttime sleep opportunity (left panels) and for a scenario with a nighttime duty period (light blue) with an 8-h daytime sleep opportunity (right panels). Note that in the day work scenario, the sleep opportunity is ended (e.g. through use of an alarm clock) somewhat prematurely, as there is still some homeostatic pressure for sleep left to be dissipated (top left). In the night work scenario, however, sleep is curtailed much more, with the rising circadian wake pressure causing awakening from daytime sleep well before the end of the sleep opportunity. The early awakening leaves a higher level of homeostatic sleep pressure at the end of the shortened sleep period (dark gray) and causes a portion of time available for sleep in this scenario (light gray) to remain unutilized (top right). The combined effect of the two processes—sleepiness calculated as the net difference between the homeostatic pressure for sleep and the circadian pressure for wakefulness—is that sleepiness is low and stable throughout the duty period in the daytime duty scenario (bottom left), whereas sleepiness increases and peaks toward the end of the duty period in the nighttime duty scenario (bottom right). Note that the transient cognitive impairment immediately after awakening known as sleep inertia is not depicted in this figure.