Exercise and Cognition: Part One: What the Trials Show

Abstract

Someone shopping for a supplement to think more clearly is looking for an effect. It is worth knowing how large that effect is when it comes from something free.

A 2025 meta-review in the British Journal of Sports Medicine pooled 133 systematic reviews covering 2,724 randomised controlled trials and 258,279 participants — the largest synthesis available on exercise and cognition.

This is the first of three parts. It covers what the trials found, including two results that are more interesting than the headline: the effects were larger at lower intensities, and larger in shorter interventions.

1.The Scale of the Evidence

Ben Singh, Hunter Bennett and colleagues restricted inclusion to systematic reviews and meta-analyses of randomised controlled trials, across all populations and all ages, searching eleven databases.

Data extraction and risk-of-bias scoring were done in duplicate, using AMSTAR-2 — a tool for assessing the quality of systematic reviews rather than of individual trials.

The resulting body is 133 reviews, 2,724 trials, a quarter of a million participants. For comparison, the entire randomised evidence base for L-theanine and cognition, covered elsewhere in this library, is five trials and 148 people.

That asymmetry is the reason this topic exists in a supplement company's library.

2.The Effects

Exercise significantly improved general cognition, with a standardised mean difference of 0.42. Memory improved by 0.26, and executive function by 0.24.

By the conventional reading of effect sizes, 0.42 is moderate and the other two are small. They are also, in the context of this library, unusually large: our L-theanine series reported pooled effects of 15 to 27 milliseconds on laboratory attention tasks, at low certainty of evidence.

Two subgroup findings sharpen the picture. Memory and executive function improvements were greater for children and adolescents than for adults and older adults. And people with attention-deficit hyperactivity disorder showed greater improvement in executive function than other populations.

The ADHD finding is worth holding beside our research note on theanine and paraxanthine in ADHD, where the intervention under test is a capsule and the effect sizes on offer are considerably smaller.

3.The Two Counterintuitive Results

Effects were generally larger for low- and moderate-intensity interventions than for high-intensity ones.

And shorter interventions, of one to three months, together with exergames — video games requiring physical movement — produced the largest effects on general cognition and memory.

Both cut against intuition, and both deserve scepticism rather than enthusiasm.

A pattern in which shorter and easier interventions produce larger effects is the signature that meta-analysts look for when they suspect small-study effects. Short, low-intensity trials are cheap, tend to be small, and small trials with null results are less likely to be published. The observed gradient may be describing the literature rather than the physiology.

The alternative reading is real and also worth stating: adherence is better in shorter, gentler programmes, and an intervention people complete may outperform one they abandon.

The meta-review reports that findings remained statistically significant under its sensitivity analyses. What it cannot do is distinguish those two explanations, because both would produce the same pattern.

4.What an Effect on a Cognitive Test Is

The outcomes here are general cognition, memory and executive function as measured by neuropsychological instruments — the same class of measure used in supplement trials, which is what makes the comparison fair.

It is also what limits it. A standardised mean difference of 0.42 on a battery of cognitive tests is not a statement about how someone's work goes, how much they remember of a conversation, or how their thinking ages.

Part Three takes up that gap directly, with the largest long-term observational analysis available — and the answer it gives is markedly less encouraging than this one.

Editorial Comment

MindHeaven® sells supplements. This article reports that the best-evidenced intervention for cognitive performance is exercise, at effect sizes larger than anything in our category, from something that costs nothing.

We publish it because it is true, and because a library that only covered compounds would be a catalogue with citations. If the question is how to think more clearly, the honest ordering of the evidence puts movement, sleep and hearing before any capsule — including ours.

That is not modesty. It is the only position from which anything else we write can be believed.

A note on sources. This topic was filed around a 2025 meta-review in Psychological Bulletin and two further meta-analyses, all three closed access with no open copy obtainable. We substituted three open syntheses — this meta-review, a network meta-analysis comparing exercise types, and a long-term observational meta-analysis in JAMA Network Open — and consider the replacement set at least as strong.