Exercise does not grow your brain
The famous 2011 trial found a 2% hippocampus increase in 120 older adults. The meta-analysis of 14 controlled trials found no effect on total hippocampal volume across 737 people.
We have not finished checking this source. No judgement either way. how we score evidence
Caveat on this rating: The 2011 trial carries a published rebuttal in the same journal: Coen, Lawlor and Kenny, "Failure to demonstrate that memory improvement is due either to aerobic exercise or increased hippocampal volume", PNAS 2011;108(18):E89, author reply E90, doi 10.1073/pnas.1102593108. A 2% change in a subregion sits near the limit of what structural MRI resolves reliably in 120 people, and the anterior hippocampus is a smaller compartment measured more noisily than total volume. The meta-analysis found the left-hippocampus effect only, and attributed it post-hoc to prevented decline - a post-hoc subgroup result, weaker than the headline sounds. Neither study enrolled depressed people or measured mood, so neither supports any claim about exercise and emotional health. Animal models show hippocampal growth consistently; the human evidence is called equivocal by these authors.
Exercise does not grow your brain. It appears to slow one part of it shrinking, in older adults.
The study everyone quotes is real. In 2011, 120 older adults were randomised, and aerobic training raised the volume of the front of the hippocampus - a memory structure - by 2%. The control group's shrank.
Then researchers pooled every controlled trial they could find.
No effect on total hippocampal volume, across 737 people
Fourteen trials. The one significant result was on the left side alone, and the authors' own follow-up analysis said it came from exercise preventing the shrinkage that happens with age. Retention, not growth.
Three phrases we will not use. "Grey matter" - neither study measured whole-brain grey matter. "Brain density" - neither reports density at all. And the 2011 trial measured spatial memory, not mood.
We also looked for evidence that exercise raises optimism. The research mostly runs the other way: optimistic people exercise more.
Worth noticing
Move for how you feel this week. That is the claim the evidence actually carries.
Source
Effect of aerobic exercise on hippocampal volume in humans: A systematic review and meta-analysis — Firth J, Stubbs B, Vancampfort D, Schuch F, Lagopoulos J, Rosenbaum S, Ward PB (2018)
Read the source: https://doi.org/10.1016/j.neuroimage.2017.11.007
DOI: 10.1016/j.neuroimage.2017.11.007
How this was scored
- Study design
- Meta-analysis of randomised trials
- Funding
- not recorded
- Published in
- not recorded
- Sample size
- 737
- Preregistered
- not recorded
- Conflicts disclosed
- not recorded
- Independent of proponent
- not recorded
- Retracted
- No
We have not finished checking this source, so there is no scoring to show yet. “We have not checked this yet” and “this is disputed” are different statements, so no scored band is shown rather than a low one.
Read the full scoring rubric, including what it can't tell you.
Published August 31, 2026.
Questions
How strong is the evidence behind this?
Resolv rates this source "not yet assessed". We have not finished checking this source. No judgement either way. One caveat travels with that badge: The 2011 trial carries a published rebuttal in the same journal: Coen, Lawlor and Kenny, "Failure to demonstrate that memory improvement is due either to aerobic exercise or increased hippocampal volume", PNAS 2011;108(18):E89, author reply E90, doi 10.1073/pnas.1102593108. A 2% change in a subregion sits near the limit of what structural MRI resolves reliably in 120 people, and the anterior hippocampus is a smaller compartment measured more noisily than total volume. The meta-analysis found the left-hippocampus effect only, and attributed it post-hoc to prevented decline - a post-hoc subgroup result, weaker than the headline sounds. Neither study enrolled depressed people or measured mood, so neither supports any claim about exercise and emotional health. Animal models show hippocampal growth consistently; the human evidence is called equivocal by these authors. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
Effect of aerobic exercise on hippocampal volume in humans: A systematic review and meta-analysis — Firth J, Stubbs B, Vancampfort D, Schuch F, Lagopoulos J, Rosenbaum S, Ward PB (2018). DOI: 10.1016/j.neuroimage.2017.11.007. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Meta-analysis of randomised trials. Funding: not recorded. Independence from the proponent is not recorded. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.