Kids who run are more likely to have faster nerve activities.

Researchers have found that in 9- and 10-year-olds, those who are more aerobically fit have more compact white matter. White matter is made up of axons that carry nerve signals from one area of the brain to another. Therefore, more compact white matter means there is faster and more efficient nerve activity.

The study, published in Frontiers in Human Neuroscience, uses diffusion tensor imaging to look at white matter tracts in 24 participants. This method looks at water diffusion into brain tissue. The more water diffusion, the less compact and fibrous the white matter.

After controlling for variables that could have contributed to differences in the fitness of the brain, the researchers' analyses found several fitness-related differences in white-matter tracts of the brain - especially in the tracts that affect attention and memory: the corpus callosum, the superior longitudinal fasciculus and the superior corona radiata.

"Previous studies suggest that children with higher levels of aerobic fitness show greater brain volumes in gray-matter brain regions important for memory and learning," said Laura Chaddock-Heyman, a postdoctoral researcher involved with the study. "Now for the first time we explored how aerobic fitness relates to white matter in children's brains."

Although this study did not look at cognitive differences between children, previous research has shown a link between aerobic fitness and cognitive function in other age groups.

"Previous studies in our lab have reported a relationship between fitness and white-matter integrity in older adults," said Arthur Kramer, director of the Beckman Institute and one of the professors involved in the study. "Therefore, it appears that fitness may have beneficial effects on white matter throughout the lifespan."

Now the team is in the next stage of its research: a five-year randomized, controlled trial aimed at determining whether kids who start and maintain a fitness routine see increased integrity in their white-matter.

They are currently two years into their trial, and they hope to have a more complete view of the relationship between aerobic exercise and brain health.

This study adds to the existing evidence that exercise, especially aerobic exercise, helps improve cognitive function in the brain.