Cognitive Performance and Sleep Inertia in Shift Work

Shift work disrupts the alignment between the biological clock and work hours, leading to impaired alertness, slowed reaction times and reduced decision-making capacity upon awakening or during night shifts. The phenomenon of sleep inertia—a transient decline in cognitive performance and subjective alertness following sleep offset—exacerbates risks in safety-critical professions such as healthcare, transport and emergency services. Labour patterns that fragment sleep, such as extended shifts and on-call duties, intensify circadian misalignment and deepen sleep inertia. Research has sought to characterise how sleep architecture, nap timing and recovery strategies influence vigilance, working memory and psychomotor speed. Understanding these interactions has global significance for occupational health policy, shift scheduling and real-world countermeasures designed to safeguard performance and well-being in around-the-clock operations.

Research from Nature Portfolio

A controlled laboratory study compared a single 120-minute monophasic nap with a split schedule of 90-minute and 30-minute naps during a simulated 16-hour night shift. Findings indicate that although total sleep time increased with longer naps, subjective fatigue and drowsiness immediately after awakening were higher when deep-sleep latency shortened. The split-nap protocol attenuated fatigue and drowsiness through the pre-dawn hours compared with both no-nap and single-nap conditions. However, neither nap strategy yielded significant improvements in cognitive throughput during morning assessments. These results highlight the complexity of balancing sleep duration, sleep stages and operational feasibility when designing nap schedules to mitigate sleep inertia in shift work.

Cognitive Performance and Sleep Inertia in Shift Work publication trend

The graph below shows the total number of articles in cognitive performance and sleep inertia in shift work across all publications each year (not limited to Nature Index journals).

Technical terms

Sleep inertia: A transient impairment in alertness and performance immediately after awakening.

Circadian rhythm: The endogenous ∼24-hour cycle regulating physiological and behavioural processes.

Slow-wave sleep: The deepest stage of non-rapid eye movement sleep, associated with high-amplitude, low-frequency brain waves.

Split nap: A sleep strategy dividing rest into two separate nap opportunities within a shift.

Psychomotor Vigilance Task: A sustained-attention test measuring reaction time to visual stimuli, used to assess alertness.

References

1. Effects of 90- and 30-min naps or a 120-min nap on alertness and performance: reanalysis of an existing pilot study. Scientific Reports (2023).
2. Strategic naps in automated driving − Sleep architecture predicts sleep inertia better than nap duration. Accident Analysis & Prevention (2024).
3. Exercising Caution Upon Waking–Can Exercise Reduce Sleep Inertia?. Frontiers in Physiology (2020).
4. Sleep and recovery in physicians on night call: a longitudinal field study. BMC Health Services Research (2010).