I rarely nap, but when I do it’s absolutely delicious. To me, there are few things better than a Sunday afternoon couch nap in the sun (perhaps I was a cat in a past life). Yet, sometimes you can wake from a nap feeling just as unrested as when you started, in fact your grogginess level can be worse. Why could a few minutes of zzzz’s lead to such feelings?
In 1995, NASA performed a study to evaluate the benefits of napping in long-flight pilots. Pilots were divided into a Rest Group and a No-Rest Group (yes, very creative names, but you get the picture) and evaluated, over the course of a series of trans-Pacific flights, on their performance and sleepiness level. Pilots in the Rest Group were given a 40-minute window of opportunity to nap as researchers wanted to reduce likelihood of pilots progressing into slow wave sleep (stages 3 & 4; I will explain why later). A whopping 93% were able to nap in the Rest Group, while those in the No-Rest Group were required to maintain normal flight activities during their 40-minute “rest” window. Pilots, on average, fell asleep in 5.6 minutes and slept for 25.8 minutes.
Not surprisingly, pilots in the Rest Group demonstrated a 16 per cent improvement in reaction time and a 34 per cent improvement in concentration relative to the No-Rest Group. Sleepiness, as measured by EEG during the last 90 minutes of the flight, was lower in the Rest-Group with 34 micro-events (physiological changes in EEG waves indicative of micro-sleeps) relative to 120 micro-events in the No-Rest Group. It’s a little frightening to think of our pilots to be this sleepy during their shift, but it isn’t surprising.
Following this study, NASA started to promote the benefits of the 26-minute nap for astronauts and long-flight pilots. Why just 26 minutes? Well, pilots in the Rest Group who slept an average of 26 minutes experienced significant improvements in performance relative to pilots who didn’t. And also because after about 30 minutes of sleep, we typically enter stages 3 & 4 of our sleep cycle, commonly known as deep sleep. Stages 3 & 4 are necessary for physiological recovery (stages 2 and REM are associated with mental and cognitive recovery) and waking from these stages of sleep is often accompanied by feelings of grogginess, fatigue, and a general malaise. The further we get into our sleep cycle (typically 90 minutes in length), the more “painful” it is to awaken.
So next time you are planning an afternoon snooze or a recovery nap, it is recommended that you set your clock for 26 minutes or 90 minutes. If you’re able to do 90 minutes, you’ll achieve one entire sleep cycle and feel ready and rested; however, most of us aren’t able to take a 90 minute snooze at work, so set your clock for 26 minutes and enjoy the benefits of some mid-afternoon zzzz’s .
Now you have a legitimate and evidence-based excuse to nap (not that you needed one).