Dr. Divyangana Rakesh, senior lecturer in neuroscience and psychology at King's College London and senior author of the study, said: "This study gives us some of the clearest evidence yet that even an everyday, low-cost, accessible measure of physical activity like daily step count is tied to how adolescent brains and mental health develop. What's striking is that we don't see this benefit leveling off in the observed range, even among the most active young people in our sample."

What happened in the brain?

The study went beyond symptom counts. Adolescents with the highest step counts also showed slightly thicker brain tissue in two areas — one involved in movement, the other in regulating emotion. The researchers found that this structural difference helped explain part of the link between walking and better mental health.

In plain terms, physical activity may shape the very brain regions that keep emotions in check, and that structural change appears to account for a portion — though not all — of the mental health benefit.

Qingyang Li, lead author of the study, said: "We're starting to understand parts of the brain that might be involved in the link between daily steps and young people's mental health. It's preliminary, but it gives us a clearer idea of where to look next."

Notably, the analysis found no link between step count and academic performance. Walking more was associated with brain and mental health differences, but not with how well adolescents did at school.

Do teenagers need to become athletes?

No — and that is one of the study's most practical messages. Dr. Amanda Paluch, associate professor of kinesiology at the University of Massachusetts Amherst, said: "It is not an all-or-nothing situation. Adolescents don't need to be elite athletes to benefit. Increases of 1,000 to 2,000 daily steps, from any starting point, were associated with better brain structure and mental health outcomes, and that beneficial association keeps building from there."

She added: "The goal is finding realistic, sustainable ways to move more, through everyday opportunities like walking to school, active play and activities kids actually enjoy, so these benefits are accessible wherever an adolescent is starting from."

Adolescence is a key period for both brain development and mental health, which is why the findings carry weight: physical activity appears to benefit both at once.

What are the study's limitations?

The researchers urge caution in interpreting the results. This was an observational study, meaning it cannot prove that walking more directly improves mental health — only that the two travel together.

The link held even after the researchers accounted for the adolescents' earlier mental health problems. Still, they acknowledge an alternative explanation remains possible: teenagers with fewer problems may simply have been more active to begin with.

Two other caveats apply. The brain differences detected were small. And few adolescents in the sample had extremely high step counts, so it is unclear whether the pattern continues beyond the range measured in this study.

What comes next?

The findings point researchers toward specific brain regions — those governing movement and emotion regulation — as promising targets for future work on how everyday physical activity shapes adolescent development. As Li noted, the brain results are preliminary, but they give scientists a clearer map of where to look.

For now, the practical takeaway is modest but encouraging: an extra 1,000 to 2,000 steps a day, gained through ordinary activities like walking to school or active play, was associated with better brain structure and fewer mental health symptoms a year later — regardless of where a teenager starts.

The study, "Physical Activity and Adolescent Brain Structure, Mental Health, and Academic Performance," appears in JAMA Network Open (2026), DOI: 10.1001/jamanetworkopen.2026.36973.