Does Lifting Weights Make You Smarter? What the Research Shows

Lifting weights does not make you smarter in the sense of raising your IQ: no trial has shown that strength training changes scores on a full intelligence test. In older adults, randomized trials of resistance training show small gains on cognitive tests, about 0.3 of a standard deviation in the best-known meta-analysis, and in more than a million young Swedish men, muscle strength was not associated with intelligence at all.

That is still a useful finding for people over 60, and strength training has plenty of other health benefits. This page covers what the main resistance-training trials found, why the average effect is probably smaller than it looks, what the link between grip strength and test scores does and does not mean, and why the evidence for young adults is thin.

Most of the good evidence comes from older adults, often people who already have memory problems. Two trials are cited more than any others.

• The SMART trial: The Study of Mental and Resistance Training randomized 100 Australian adults with "mild cognitive impairment" (memory or thinking problems that are noticeable but do not yet amount to dementia), average age 70. Participants did high-intensity progressive resistance training or a sham programme of seated stretching, two to three days a week for six months, with or without computer-based brain training. Resistance training improved the main outcome, a dementia rating scale called the ADAS-Cog, and improved executive function across 18 months, measured partly with the Matrices subtest from the Wechsler adult intelligence scale. Brain training only slowed decline on the memory measures at six months.

• The Vancouver trial: Teresa Liu-Ambrose and colleagues randomly assigned 155 women aged 65 to 75 to once-weekly or twice-weekly resistance training, or to a balance-and-toning class, for a year. Both lifting groups improved on the Stroop test, a measure of attention and impulse control, by about 11% to 13%, while the toning group stayed flat. Oddly, both lifting groups also showed slightly smaller whole-brain volumes than the toning group at the end of the year, so the brain-imaging result did not line up neatly with the test result.

A follow-up analysis of SMART found that the people whose strength rose most were the people whose cognition improved most, while gains in aerobic fitness did not explain the benefit. That is an interesting clue, though an analysis within a single trial of 100 people cannot prove that strength itself is the cause.

Meta-analyses pool these and similar studies. Northey and colleagues combined 36 randomized trials of adults over 50 and found an overall exercise benefit of 0.29 standard deviations, with aerobic training, resistance training, multicomponent training and tai chi each showing a significant effect. A meta-analysis limited to resistance training, by Landrigan and colleagues, pooled 24 studies and reported larger effects on composite cognitive scores (0.71 SD) and executive function (0.39 SD), no reliable effect on working memory, and very high variation between studies.

On the IQ scale, where one "standard deviation" (a measure of how spread out scores are) equals 15 points, 0.29 SD would be about 4 points. That conversion is only a rough guide, because these trials used memory, attention and dementia screening tests, not full IQ tests, and screening scales are built to detect impairment, not to rank healthy people.

Exercise trials share several problems. Many are small, many compare exercise against no activity at all, and journals are more likely to publish positive results. An umbrella review by Ciria and colleagues in Nature Human Behaviour reanalysed the randomized trials behind 24 meta-analyses of exercise and cognition in healthy people. The raw pooled benefit was small (d = 0.22). It fell to d = 0.13 after accounting for whether the control group was active and for differences at baseline, and to a negligible d = 0.05 after correcting for publication bias. That last figure is under one IQ-scale point.

The umbrella review covered all types of exercise, so it does not single out weightlifting. It does show why a 0.7 SD effect from a pool of small resistance-training studies should not be taken at face value.

There is also the question of transfer. Psychologists distinguish "near transfer," getting better at tasks like the ones you practised, from "far transfer," improvement in broad abilities such as reasoning. Sala and Gobet's reviews of chess, music and working memory training found that far transfer to general intelligence is rare. Exercise is different, because the proposed route is through the body and brain, not practice on similar tasks, but the same test applies: a benefit on one attention test is not a rise in general intelligence.

The house page on whether exercise can affect your IQ score covers the broader exercise evidence, including the short-term effects of a workout on test day.

In large population samples, people with stronger grips tend to score a bit higher on cognitive tests. Firth and colleagues analysed about 475,000 UK Biobank participants recruited in middle and later life and found that grip strength was associated with better reasoning, memory and reaction time, even after adjusting for age, sex, body weight and education.

This is correlation, and the authors said the direction still needs to be established. Grip strength is a marker of general health in middle and later life. Illness, inactivity and ageing all lower muscle strength and cognitive scores together, so a third factor can produce the link without lifting weights doing anything for the brain.

The most informative data on young people point the other way. Åberg and colleagues linked conscription records for 1.2 million Swedish men tested at 18. Cardiovascular fitness, measured on an exercise bike, was positively associated with intelligence scores, and the association held within pairs of identical twins. Muscle strength was not associated with cognitive performance. At the age when intelligence is near its adult level, being strong told the researchers nothing about how well a young man reasoned.

If you want the fitness side of that result, the page on IQ and walking covers aerobic exercise trials.

Long-term trials of strength training in healthy young adults with good cognitive outcomes are scarce, so there is little to say about them with confidence. Most of the young-adult evidence is about a single session.

Wilke and colleagues pooled 12 trials of one bout of resistance exercise in healthy adults. Compared with resting, lifting improved performance on cognitive tests taken shortly afterwards (SMD 0.56), mainly on tasks of impulse control and mental flexibility. Lifting was no better than aerobic exercise, and the effect is a short-lived change in alertness. It says nothing about long-term intelligence.

Headlines from small trials in older adults are easy to generalise to everyone, including young people the trials never studied. Selection adds to the confusion: people who lift regularly may differ from people who do not in health, sleep and income, which makes casual comparisons between gym-goers and everyone else meaningless.

The fair summary is narrower. For older adults, especially those with early memory problems, resistance training is a reasonable way to protect function, with modest benefits on specific tests and good effects on strength and mobility. For a healthy 25-year-old, there is no evidence it will raise an IQ score.

No study has shown that it does. Trials in older adults find small improvements on attention, memory and dementia screening tests, which are not the same as an IQ score.

For older adults, randomized trials suggest modest benefits on cognitive tests, similar in size to aerobic exercise. The pooled effects are probably inflated by small studies and publication bias.

In middle-aged and older adults, grip strength is weakly linked with better test scores, likely because both reflect general health. In 1.2 million Swedish 18-year-olds, muscle strength was unrelated to intelligence.

Meta-analyses find similar effects for both in older adults. The Swedish conscript data linked aerobic fitness, not strength, with intelligence at 18, though that is a correlation.

A single bout of lifting slightly improves performance on some cognitive tasks soon afterwards. The effect is temporary and no larger than after aerobic exercise.

Lifting weights builds strength and may help older adults keep some cognitive function, but it does not make anyone smarter in the sense of raising IQ. The trials are small and mostly in older people, and in young adults strength and intelligence appear unrelated. To see where your reasoning ability stands, take a full-length online IQ test.

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Hero image: Dumbbells - Hanteln, by I G, CC BY 2.0. Via Wikimedia Commons.