(Undated) -- There’s new evidence that keeping kids active not only keeps their bodies healthy, but also their brains. "White matter" describes the bundles of axons that carry nerve signals from one area of the brain to another. Laura Chaddock-Heyman and other researchers at the University of Illinois found a link between physical fitness and the integrity of white matter tracks in the brains of nine and 10-year-old children. She says it doesn’t mean that physically fit kids are smarter, but perhaps their brains work better. She points out that previous research has shown an association between improved aerobic fitness and gains in cognitive function on specific tasks and in academic settings.