A half-hour evening workout protected memory during a short night’s sleep

Canadian researchers have shown that a single half-hour workout in the evening can mitigate the adverse effects of a short night’s sleep on memory. The study was conducted at McGill University in Montreal by Madhura S. Lotlikar and Marc Roig.

In an experiment involving 88 healthy young adults, a half-hour cycling session before a short night’s sleep – limited to 4.5 hours – helped to maintain memory at a level that was statistically indistinguishable from that achieved after a full night’s sleep. The effect is linked to the proportion of deep slow-wave sleep, but the sample size was small, and the study examined only one short night’s sleep and one type of memory; it is therefore too early to draw far-reaching conclusions.

Details

The study was published in the peer-reviewed journal *SLEEP*, which is published by Oxford University Press on behalf of the Sleep Research Society. The article is titled ‘Slow-Wave Sleep Mediates the Compensatory Effects of Acute Moderate-Intensity Exercise on Declarative Memory Deficits in Sleep Restriction’ (‘Slow-wave sleep mediates the compensatory effect of a single bout of moderate-intensity exercise on declarative memory deficits during sleep restriction’).

Eighty-eight healthy young adults were randomly divided into four groups: 8.5 hours of normal sleep without exercise; 4.5 hours of sleep restriction without exercise; exercise before normal sleep; and exercise before sleep restriction. Participants in the exercise groups cycled on an exercise bike for 30 minutes at 19:00 at a moderate pace — 55–60 per cent of their individual maximum oxygen consumption. The control groups simply sat still during this time.

At 22:00, all participants memorised 80 ‘face–name’ pairs – a standard task for declarative and episodic memory. Their sleep was recorded using polysomnography. The following morning, memory was assessed using a recognition test comprising 120 pairs: 80 previously shown pairs and 40 new ones.

Delayed recall after a short sleep with training proved to be better than after a short sleep without training, and was not statistically different from the results of both groups who had had a full night’s sleep. In other words, a single evening training session compensated for the memory impairment usually associated with a short night’s sleep. The proportion of slow-wave, deep sleep statistically mediated this relationship: the more deep sleep a participant had, the more pronounced the protective effect of the training was.

Why this is important

The findings suggest a simple and accessible way to mitigate the effects of a single short night’s sleep on memory — training, rather than medication or a device. This could be useful, for example, for shift work, on-call duties or a busy exam period, when a full night’s sleep is temporarily unavailable.

The study has limitations. It was a one-off experiment involving a single short night’s sleep, rather than an investigation into regular training or chronic sleep deprivation, which is more harmful to health than a single such night. Only one type of memory was tested — the ability to remember ‘face–name’ pairs — so it is unclear whether the effect extends to other cognitive tasks. The statistical link between the proportion of slow-wave sleep and the benefits of the training points to a likely mediator, but does not prove a specific biological mechanism. The participants were exclusively healthy young adults, so the results may not necessarily be replicated in older people or those with sleep disorders.

Source

Madhura S. Lotlikar, Marc Roig. ‘Slow-Wave Sleep Mediates the Compensatory Effects of Acute Moderate-Intensity Exercise on Declarative Memory Deficits in Sleep Restriction’. SLEEP, 2026. DOI: 10.1093/sleep/zsag235. The study was conducted at McGill University, Montreal, Canada.