A Nap and 20 Minutes of Exercise May Help Memory After Sleep Loss

You know the situation: perhaps you have managed only four hours of sleep, a packed day lies ahead, and coffee will take you only so far.

Should you fit in a nap, or carry on and do a workout instead?

Nap or exercise after sleep loss?

New research in Proceedings of the National Academy of Sciences indicates that, for memory, a nap and 20 minutes of exercise could deliver broadly comparable benefits.

Scientists at Canada's McGill University asked 54 healthy young adults to remain awake for an exhausting 30 consecutive hours in laboratory conditions, before dividing them into three groups.

One group completed 20 minutes of moderate-to-vigorous cycling. A second had a 90-minute nap. For comparison, the control group spent 20 minutes sitting on an exercise bike without pedalling.

Soon afterwards, participants viewed a collection of images without being told to commit them to memory. Three days later, they were asked which images they could recognise.

Those who napped and those who exercised both recalled substantially more images than people in the control group.

The improvement was almost the same in each case: recognition was 23 per cent better among nappers and 21 per cent better among exercisers, relative to the control group.

There was no statistically meaningful difference between the two interventions.

The findings echo a 2023 study from the University of Portsmouth, which showed that 20 minutes of moderate cycling enhanced cognitive performance in people who were partly or completely sleep-deprived, including in low-oxygen environments.

EEG results reveal different routes to better memory

What makes the latest study particularly notable is that the researchers also monitored brain activity with electroencephalography (EEG). Although both groups achieved a similar outcome, they appeared to reach it through entirely different neurological pathways.

Among the nap group, researchers identified signs that sleep pressure and brain fatigue had fallen, including a reduction in slow-wave activity. The 90 minutes seemed to have genuinely restored some lost rest, which is unsurprising because participants had slept more.

The greater the fall in this fatigue-related signature, the more successfully people later recognised the images.

Almost none of this pattern appeared in the exercise group. Their fatigue indicators remained as high as those seen in the control participants, who had done nothing at all; the workout did not appear to leave them feeling less tired.

Instead, their improved memory corresponded with a very different group of signals: those directly associated with how efficiently the brain processed images as they were being viewed.

Put simply, the nap gave the brain rest. Exercise did not rest it, but nevertheless seemed to help it function more effectively.

"Sleep loss affects nearly every aspect of how we think and function, but many people can't simply stop what they're doing and get more sleep," says Marc Roig, the study's senior author and a sports scientist at McGill's School of Physical and Occupational Therapy.

"Our findings show that even a brief bout of exercise may help preserve one of our most important cognitive abilities."

Exercise when a nap is not possible

That difference is especially relevant to people with little choice in the matter.

As neuroscientist Madhura Lotlikar, the study's first author, notes, many of those who could benefit most - nurses, pilots, new parents and night-shift workers - cannot simply take a nap during a shift.

"Exercise is accessible, inexpensive, and easy to implement. That makes it a promising tool to help people stay cognitively sharp when sleep is limited," explains Lotlikar.

Neither approach should be treated as an ideal alternative to a proper night's sleep. The researchers stress that a workout and a nap are temporary measures, rather than replacements: they may help you get through an unavoidable day, but are not a long-term way to live with reduced rest.

That matters because an estimated 20 to 40 per cent of adults globally already fail to get enough sleep. RAND has estimated that the resulting shortfall costs the US, UK, Germany, Japan and Canada a combined $680 billion annually in lost economic output.

So, when you are facing a day after just four hours of sleep, a nap may be the most useful option if one is available.

When it is not, a brisk 20-minute walk or cycle could offer more than a temporary distraction from tiredness. It appears to provide a genuine benefit to the brain, whether or not it leaves you feeling less exhausted.

The research was published in Proceedings of the National Academy of Sciences.

This article was fact-checked and edited by Rebecca Dyer. Although we take pride in our process, we are only human. If you notice an error, please let us know.