As part of our Biohacking Masterclass Series, we will explore a number of different techniques and practices to improve your daily performance. This series will range from obvious subjects like exercise and nutrition to fringe subjects like breathing techniques and sleep hygiene. Consult your physician before implementing any of these topics. We are not your physician. Note: This post may contain affiliate links to the products we use.
Unlike the sleep you get at night, hitting the pillow too long in the middle of the day can wreak mental havoc. While sleeping 9 hours at night instead of 8 will boost mental and physical performance, choosing a longer 1 hour nap over the short 20 minute nap could leave your brain slow and foggy. This phenomenon, called ‘sleep inertia’, has helped sleep researchers unlock the optimal window for power naps - the naps that are gaining popularity for their short duration and immediate cognitive and physical benefits. [1-7]
Specifically, sleep researchers define sleep inertia as “the transitional state between sleep and wake, marked by impaired performance, reduced vigilance, and a desire to return to sleep” . In other words, sleep inertia might be characterized more simply as the grogginess one occasionally feels upon waking (perhaps more commonly experienced after a short night of sleep). Sleep inertia is associated with sleepers who wake after entering into deeper non-REM stages (SWS, stages 3&4 NREM).
What window enables a sleeper to take advantage of a nap’s performance enhancing benefits while avoiding the fog that might ensue?
On the high end, a NASA study found 26 minutes of sleep time was associated with significantly improved performance and psychological alertness. In this study, crewmembers averaged a sleep latency (time to fall asleep) of approximately 5.6 minutes so the total nap ‘window’ was just over 31 minutes. Subjects were able to spend 20 minutes recuperating from any sleep inertia after the nap before performance was tested. 1
Other studies have gone on to show that shorter naps lead to less time spent recovering from inertia. When comparing 30 minute naps to 10 minute naps, researchers found benefits in both groups. Unlike the 30 minute group, the participants who took 10 minute naps saw no delay caused by sleep inertia. Some of the performance-boosting effects of 10 minute naps include “improved subjective and objective alertness, decreased fatigue, increased vigor, and improved performance” [2-7]
In a subsequent study, researchers evaluated the impact of 5, 10, 20, and 30 minute naps on performance. The 10, 20, and 30 minute naps led to improvements in performance and cognitive alertness. The 5-minute nap and no-nap groups saw no such improvements. The 10-minute group gained immediate benefits while the 20- and 30-minute subjects had to wait between 35 and 155 minutes for sleep inertia to wear off. Specifically, the 20-minute group did not see performance gains until 95 minutes after waking.  This study was repeated with sleep deprived participants in another lab and led to nearly identical overall results. [2-7]
How many minutes ahead should you set your alarm?
According to several of the studies and NASA’s crewmember experiments, set your total head-on-pillow through alarm napping window between 10 and approximately 30 minutes. If you have tracked your sleep with biometric wearables and know your average sleep latency (time to fall asleep), account for that when planning your alarm.
What is good timing for a power nap on a given day?
Generally, your circadian rhythm follows periods of alertness and periods of sleepiness. Peak sleepiness obviously occurs at night following sunset and cooling temperatures. There is also a period of sleepiness that occurs in the afternoon, a phenomenon called the post-prandial alertness dip.
The post-prandial dip is a biologically hardwired lull in alertness that happens in all humans in the midafternoon hours every day. This genetically-driven drop in attention is a cue to take a nap, making it the perfect placement for a 10-minute “power nap”.
- Rosekind et al. Alertness management: strategic naps in operational settings. J Sleep Res. 1995. Suppl. 2, 62-66.
- Milner et al. Benefits of napping in healthy adults: impact of nap length, time of day, age, and experience with napping. J. Sleep Res. 2009. 272-281.
- Trotti, Lynn Marie. Waking up is the hardest thing I do all day Sleep inertia and sleep drunkenness. Sleep Med Rev. 2018.
- Brooks, A. J. and Lack, L. C. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep, 2006, 29: 831–840.
- Tietzel, A. J. and Lack, L. C. The short-term benefits of brief and long naps following nocturnal sleep restriction. Sleep, 2001, 24: 293–300.
- Tietzel, A. J. and Lack, L. C. The recuperative value of brief and ultrabrief naps on alertness and cognitive performance. J. Sleep Res., 2002a, 11: 213–218.
- Tietzel, A. J. and Lack, L. C. Alertness and cognitive performance benefits associated with brief daytime naps. Sleep, 2002b, 25 (Abstract Supplement): A402