The Study
Brain-derived neurotrophic factor in human cerebrospinal fluid is elevated after exercise.
This study just watched what happened to 13 fit people after they rode a bike for two hours and measured a brain chemical called BDNF. It saw that in some people, the chemical went up — but we don’t know if the bike caused it, or if something else like low blood sugar did. So it doesn’t prove anything, it just shows a pattern in a tiny group.
Analysis score
Maximum 44 for a cross-sectional study.
Where the score came from
Scientists measured a brain chemical called BDNF in people’s blood and spinal fluid before and after they cycled hard for 2 hours.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 544 / 100
Quality score
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1This suggests exercise may help the brain make more BDNF, but the effect varies between people and doesn’t clearly show up in standard blood tests.
- 2BDNF in spinal fluid went up 2.8 times in 9 out of 13 people, but dropped in the other 4.
- 3Blood showed more active BDNF leaving the brain, but overall brain release didn’t change much.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Journal of neurophysiology
Year
2026
Authors
J. Carr, J. Koep, Jennifer S Duffy, L. M. Brewster, Jordan D. Bird, Justin A Monteleone, Tenasia D R Monaghan, H. Islam, Andrew R Steele, C. Howe, D. MacLeod, P. N. Ainslie, K. Thomas, T. Gibbons
Related Content
Claims (6)
After 2 hours of intense cycling, brain-derived neurotrophic factor (BDNF) levels in cerebrospinal fluid increased 2.8-fold in 9 out of 13 healthy young adults, while the other 4 showed a 4–30% decrease.
BDNF levels in cerebrospinal fluid are vastly lower than in arterial blood, and this difference shows that BDNF moves between the brain and bloodstream mainly through blood vessels, not through cerebrospinal fluid.
During the exercise protocol, all participants experienced low blood sugar due to arterial hypoglycemia, but it was not established whether this low blood sugar caused increases in brain-derived neurotrophic factor in the blood or cerebrospinal fluid.
After exercise, changes in BDNF levels in the fluid surrounding the brain and spinal cord do not match changes in BDNF levels in the blood arteries or veins, meaning the brain's BDNF changes are not driven by BDNF moving in from the bloodstream.
After two hours of intense cycling, the concentration of free brain-derived neurotrophic factor (BDNF) is higher in venous blood leaving the brain than in arterial blood entering the brain in healthy young adults, but this difference does not change significantly from resting levels.
Physical activity that causes muscles to contract raises levels of brain-derived neurotrophic factor in the blood, leading to improved adaptability and function of neurons in the brain.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.