We've all been there: it's 3pm and keeping your eyes open has become a real struggle. You spent the previous night tossing and turning, achieving a less-than-optimal sleep score as a result, and now you're struggling to think straight. All you really want is to curl up on the sofa for an hour and give yourself a top-up to get through the rest of the day.
But according to a new study led by researchers at McGill University in Canada, that might not be the best way to counter the effects of sleep deprivation on memory
The research suggests that 20 minutes of exercise may be as effective as 90 minutes of shut-eye for helping people form new memories after sleep deprivation. Here's what the study found.
What did the study find?
The researchers got 54 healthy adults aged 18-35 to stay awake for 30 hours in a lab before assigning them to one of three groups.
One group did 20 minutes of aerobic cycling on a stationary bike at 80% of their max heart rate and one group napped for 90 minutes, while the control group simply sat on the stationary bike without pedalling for 20 minutes.
Participants in each group then waited 30 minutes before viewing 150 images. Three days later, they undertook a recognition test – designed to test how well they had formed new memories after sleep deprivation – in which they were shown a combination of previously seen and new images and asked which they recognised.
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Interestingly, the group who did 20 minutes of exercise performed almost as well on the memory test as the group who napped (the former had a 21% higher memory hit rate than the control group, compared to the latter having a 23% higher rate), suggesting that exercise could be just as effective at giving the brain a boost following sleep deprivation.
And as well as the memory benefits, those who exercised didn’t report feeling any more fatigued than the group who simply sat on the bike – despite the exercise group sweating it out on a bike for 20 minutes. Although perhaps unsurprisingly, the nappers reported feeling less fatigued than the exercisers.
What does this mean for us?
‘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,’ senior author Professor Marc Roig noted. ‘Our findings show that even a brief bout of exercise may help preserve one of our most important cognitive abilities.’
‘A nap isn't always possible in the middle of a shift,’ added the study’s lead author Madhura Lotlikar. ‘Exercise is accessible, inexpensive and easy to implement. That makes it a promising tool to help people stay cognitively sharp when sleep is limited.’
However, the researchers stress that this study doesn’t mean exercise can replace sleep – rather, that it may be a powerful intervention to help you function better when a nap isn’t possible and bedtime is still some way off.
Many bodily processes crucial for repair and recovery occur when we sleep, which is why virtually every expert Women's Health has spoken to views it as one of the most important, if not the most important, things we can do for health and longevity.
Indeed, researchers found that exercise and napping appeared to protect participants’ memory via different mechanisms. The nap reduced the brain’s sleep pressure (that building feeling of a need to sleep), effectively refreshing it and helping it stay receptive to new information. Meanwhile, the workout seemed to help participants’ brains utilise the attention and memory-processing resources it still had left.
Why intensity likely matters
While this study didn't test to see whether different workout intensities make a difference to the recorded benefits, existing research does suggest that the intensity at which you exercise matters for reaping the cognitive rewards.
The researchers highlighted a previous study in which participants completed 15 minutes of low-intensity cycling post-sleep deprivation, and found no improvement in cognitive performance.
Meanwhile, another small study found that repeated bouts of moderate exercise during 30 hours of sleep deprivation were associated with slower reaction times and more negative mood changes, including greater fatigue and reduced vigour – possibly due to excessive stress on the body.
That’s why this study used the duration (20 minutes) and intensity (moderate to high) it did – hoping that it would be stimulating enough without causing too much fatigue.
The bottom line
This was a relatively small study done solely on healthy adults; more research is needed to establish how factors such as optimum intensity, duration and activity type influence the outcome.
But the findings add to a growing body of evidence on the powerful benefits of physical activity for cognitive health. Why not give 20 minutes of exercise a go the next time a nap isn’t possible?
Hannah Bradfield is a Senior Health and Fitness Writer for Women’s Health UK. An NCTJ-accredited journalist, Hannah graduated from Loughborough University with a BA in English and Sport Science and an MA in Media and Cultural Analysis. She has been covering sports, health and fitness for the last five years and has created content for outlets including BBC Sport, BBC Sounds, Runner’s World and Stylist. She especially enjoys interviewing those working within the community to improve access to sport, exercise and wellness. Hannah is a 2024 John Schofield Trust Fellow and was also named a 2022 Rising Star in Journalism by The Printing Charity. A keen runner, Hannah was firmly a sprinter growing up (also dabbling in long jump) but has since transitioned to longer-distance running. While 10K is her favoured race distance, she loves running or volunteering at parkrun every Saturday, followed, of course, by pastries. She’s always looking for fun new runs and races to do and brunch spots to try.
