After a restless night, an afternoon nap may seem like the obvious answer to fading concentration and mental fog. New research suggests that a brief session of aerobic exercise could offer a similarly powerful memory boost when sleep is limited.

Researchers at McGill University in Canada examined whether exercise could help people form new memories after sleep deprivation. Their findings indicate that 20 minutes of exercise may be nearly as effective as 90 minutes of sleep.

The study involved 54 healthy adults aged 18 through 35. Each participant remained awake in a laboratory for 30 hours before researchers assigned them to one of three groups.

One group completed 20 minutes of aerobic cycling on a stationary bike at 80% of maximum heart rate. A second group took a 90 minute nap, while a control group sat on a stationary bike for 20 minutes without pedalling.

After their assigned activity, participants waited 30 minutes and then viewed 150 images. Three days later, they completed a recognition test involving a mixture of previously viewed and new images.

Researchers asked participants to identify the images they remembered seeing. The test was designed to measure how successfully they had formed new memories following the prolonged period without sleep.

The exercise group performed almost as well as the nap group. Participants who cycled recorded a memory hit rate 21% higher than the control group, while those who napped achieved a rate 23% higher than the control group.

The findings suggest that a short workout could provide a meaningful cognitive lift after sleep deprivation. Despite cycling for 20 minutes, participants in the exercise group did not report feeling more fatigued than those who merely sat on the bike.

The nap group did report feeling less fatigued than the people who exercised. That difference points to an important distinction between improving memory performance and easing the subjective feeling of tiredness.

‘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.’

Lead author Madhura Lotlikar said a nap is not always possible in the middle of a shift. She described exercise as accessible, inexpensive and easy to implement, making it a promising option for staying cognitively sharp when sleep is limited.

However, the researchers stressed that exercise should not be viewed as a replacement for sleep. Instead, it could serve as a useful intervention when a nap is unavailable and bedtime remains hours away.

Sleep remains crucial because many bodily processes involved in repair and recovery occur during that time. The study also suggested that napping and exercise protected participants’ memories through different mechanisms.

The nap reduced sleep pressure, which is the growing feeling of needing to sleep. This appeared to refresh the brain and help it remain receptive to new information, while exercise seemed to help the brain use its remaining attention and memory processing resources.

The study did not test whether different workout intensities would produce different results. However, the researchers cited an earlier study in which 15 minutes of cycling at low intensity after sleep deprivation did not improve cognitive performance.

Another small study found that repeated bouts of moderate exercise during 30 hours without sleep were associated with slower reaction times and more negative mood changes. Those changes included greater fatigue and reduced vigour, possibly because of excessive stress on the body.

For the latest study, researchers selected 20 minutes of exercise at moderate to high intensity, seeking a level that would stimulate participants without causing too much fatigue. The research involved a relatively small group consisting entirely of healthy adults.

More research is needed to determine how workout intensity, duration and activity type might influence the cognitive effects. For now, the findings suggest that when a nap is impossible after lost sleep, 20 minutes of appropriately demanding exercise may help memory without worsening perceived fatigue.