20 minutes of cycling after an all-nighter matches a 90-minute nap for memory, study finds

There are times when you need to memorize something new the day after pulling an all-nighter. Most people try to catch even a few minutes of sleep — but a new study finds that 20 minutes of cycling produces the same memory benefit as a 90-minute nap.

After keeping participants awake for 30 hours, researchers applied each method separately and found that both groups scored an average of 22 percent higher on memory tests than those who did nothing.

The findings were published in the Proceedings of the National Academy of Sciences (PNAS), Vol. 123, No. 32, by researcher Madura Lotlikar and professor Marc Roig of McGill University in Canada, along with colleagues from the Jewish Rehabilitation Hospital in Montreal.

The study enrolled 54 healthy adults between the ages of 18 and 35 who did not work shift schedules, did not take sleep medication and had no aversion to exercise. Participants arrived at the laboratory at 9 p.m. and stayed awake for 30 hours under the researchers' supervision.

The sleep-deprived participants were divided into three groups. One group pedaled a stationary bike for 20 minutes at roughly 80 percent of their maximum heart rate — an intensity vigorous enough to cause breathlessness. A second group was allowed to sleep for 90 minutes. The third group sat on a stationary bike for 20 minutes without pedaling.

Thirty minutes later, all three groups were shown 150 photographs. The researchers did not tell participants they would be tested on the images later.

Three days later, participants returned for a memory test. The 150 original photographs were mixed with 75 new images, and participants were asked to identify which ones they had seen before.

The group that had done nothing scored 46 percent. The cycling group scored 56 percent and the nap group 57 percent — 10 and 11 percentage points higher, respectively, than the control group.

Both exercise and napping proved effective at preserving memory, with only a marginal difference between them. In effect, the 20-minute cycling group and the 90-minute nap group performed identically.

The research team also measured fatigue to address a natural concern: that exercising after an all-nighter might leave people even more worn out.

Throughout the experiment, participants were asked to rate their level of tiredness every two hours.

As expected, the nap group showed a clear reduction in fatigue. The exercise group and the seated control group, however, reported no difference in tiredness from each other.

Exercise did not add to fatigue beyond what the all-nighter itself caused — yet the exercise group still outperformed the control group on memory.

The study also turned up a striking finding in brain activity. The researchers attached 64 electrodes to each participant's scalp while they viewed the photographs and recorded their brainwaves. The group that had done nothing after the all-nighter showed the most intense neural activity of all three groups.

When a person pays attention to something, a specific electrical signal rises in the brain about 0.3 seconds later. A stronger signal is generally associated with better subsequent recall.

The control group produced the strongest signal of the three — yet had the worst memory scores. The researchers interpreted this as the brain straining to compensate for exhaustion.

The exercise group, by contrast, generated a weaker signal but achieved higher memory scores, suggesting the brain was working more efficiently — doing more with less.

However, the research team cautioned against reading too much into the results, stressing that exercise cannot substitute for the many other functions that sleep serves.

The team also acknowledged the study's limitations: the sleep deprivation was induced in a laboratory setting over a single night, which differs from the chronic sleep deficits experienced by shift workers over months. The participant pool was also limited to healthy young adults.

The researchers noted that the conditions were not perfectly matched — the nap lasted 90 minutes while the exercise lasted only 20 — explaining that a 20-minute nap would not allow participants to reach deep sleep, while 90 minutes of exercise would cause excessive fatigue, making equal durations impractical.

Meanwhile, between 20 and 40 percent of adults worldwide are chronically sleep-deprived. Sleep deprivation is estimated to cost five OECD member countries alone $680 billion a year in lost productivity.

DOI: 10.1073/pnas.2528246123

M.S. Lotlikar, B. Ayotte, A. Choi, F. Seo, E.M. Robertson, F.D. Maso, & M. Roig, "Protecting episodic memory after sleep loss: Similar benefits of exercise and naps via distinct neural contributions," Proc. Natl. Acad. Sci. USA. 123 (32) e2528246123, (2026).