It’s long been known that exercise improves a person’s brain health – and researchers now think they better understand at least one of the factors at play.

Just one 15-minute session of aerobic exercise floods the brain with brain-derived neurotrophic factor (BDNF), a protein known to support the health of new and existing brain cells, researchers will report in the June 2026 issue of the journal Brain Research.

What’s more, as a person’s fitness increases, so does the amount of BDNF released following exercise, researchers found.

“We’ve known for a while that exercise is good for our brain, but the mechanisms through which this occurs are still being disentangled,” said lead researcher Flaminia Ronca, an associate professor with University College London in the U.K.

“The most exciting finding from our study is that if we become fitter, our brains benefit even more from a single session of exercise, and this can change in only six weeks,” Ronca said in a news release.

For the new study, researchers recruited 30 out-of-shape folks to take part in a 12-week fitness program involving four sessions a week on an exercise bike.

Overall, the fitness program did not significantly alter the participants’ baseline BDNF levels when they were at rest.

But by the final week, participants had a larger spike in BDNF levels following intense exercise, compared to how their brains responded at the start. This increased spike was linked to improvements in their aerobic fitness.

These higher BDNF levels also were associated with positive changes in the prefrontal cortex – the part of the brain responsible for decision-making and self-control – during brain function tests.

“These results suggest that increasing physical fitness can enhance BDNF transcription in response to acute bouts of exercise. This might, in turn, play a part in the modulation of neural function during executive tasks after acute exercise,” researchers concluded.