Unsolved Issues: Part V, Amber Berlin
Are you tired? Maybe you need a nap.
Naps decrease the homeostatic drive for sleep by reducing the number of hours continuously awake, which results in a greater ability to focus. It’s like a reboot for your brain, shutting down the conscious processes of thought in favor of cellular recovery and the cleanup of waste chemicals. Studies indicate pilots afforded sleep during in-flight crew rest performed better on cognitive tests than those pilots who were only given a rest period where sleep was not permitted. But to most effectively combat aviation fatigue, when is the best time of day to take a nap? And how long should you nap to get the most benefit?
The best time of day to nap is during a Window of Circadian Low. The Window of Circadian Low refers to a specific time of day within the 24-hour circadian cycle in which subjects are primed for sleep. During times of circadian peak, the body’s physiological processes are programmed for an increased level of wakefulness. Conversely, during dips in the circadian cycle the body is gearing down for sleep.
Staying awake during a Window of Circadian Low can cause an increased level of fatigue because the pilot is working against the physiological processes which are preparing for sleep. Quite literally, you are fighting against your body to stay awake. Within the circadian cycle, researchers have identified two Windows of Circadian Low: at approximately 3am-5am and 3pm-5pm (Rosekind, Co, Gregory, and Miller, 2000). Many of us struggle through the afternoon hours yawning and drinking coffee, so if you get the opportunity, take advantage of the 3pm circadian siesta. Studies have also shown operations during a Window of Circadian Low can result in reductions in performance and alertness and increases in micro sleeps and errors (Rosekind, Gander, Connell, & Co, 2001; Caldwell et al., 2006).
The normal sleep cycle runs approximately 90 minutes and is comprised of sleep stages 1-4 and rapid-eye-movement (REM). Getting through an entire sleep cycle is a good idea, however, there are hazards to sleeping too long on your nap. Sleep inertia is defined by the Federal Aviation Administration as “… a period of impaired performance and reduced vigilance following awakening from the regular sleep episode or nap. This impairment may be severe, last from minutes to hours, and be accompanied by micro-sleep episodes” (FAA, 2010). Otherwise known as grogginess, sleep inertia can make waking up from your nap an undesirable experience as you try to get your bearings.
If you can’t get the full sleep cycle in, aim for less than 45 minutes, which reduces the occurrence of sleep inertia. By avoiding the deeper stages of sleep, you can also avoid the grogginess that comes with waking up in them. But remember, the best recovery happens in those final sleep stages and it’s important to spend as much time there as possible.
Flying unconscious….have you done it lately? Find out how you can combat aviation fatigue and this zombie-like behavior in the next Unsolved Issues: Part VI – Nocturnal Window of Unconscious Flight.
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Caldwell, J., Mallis, M., Colletti, L., Oyung, R., Brandt, S., Arsintescu L., . . . & Chapman, P. (2006). The Effects of Ultra-Long-Range Flights on the Alertness and Performance of Aviators. NASA/TM-2006-213484.
Federal Aviation Administration (2010). Advisory Circular. Basics of Aviation Fatigue. AC No. 120-100.
Rosekind, M., Co, E., Gregory, K., and Miller, D. (2000). Crew Factors in Flight Operations XIII: A Survey of Fatigue Factors in Corporate/Executive Aviation Operations. NASA/TM–2000-209610.
Rosekind, M., Gander, P., Connell, L. and Co, E. (2001). Crew Factors in Flight Operations X: Alertness Management in Flight Operations Education Module. NASA/TM-2001-211385/DOT/FAA/AR-01-01.
Featured Image: Kent Wien