Researchers have found a connection between physical fitness and children's brain development.
University of Illinois psychology professor and Beckman Institute director Art Kramer and his colleagues found differences in the brains of physically fit children and their less-fit peers.
According to the study, those who are more fit tend to have a bigger hippocampus and perform better on a test of memory than their less-fit peers.
A bigger hippocampus in nine- and ten-year-old children appears to boost their performance on a relational memory task, said University of Illinois doctoral student Laura Chaddock.
The new study used magnetic resonance imaging to measure the relative size of specific structures in the brains of 49 child subjects.
"This is the first study I know of that has used MRI measures to look at differences in brain between kids who are fit and kids who aren't fit. Beyond that, it relates those measures of brain structure to cognition," said Kramer.
The study focused on the hippocampus, a structure tucked deep in the brain, because it is known to be important in learning and memory.
Previous studies in older adults and in animals have shown that exercise can increase the size of the hippocampus.
A bigger hippocampus is associated with better performance on spatial reasoning and other cognitive tasks.
"In animal studies, exercise has been shown to specifically affect the hippocampus, significantly increasing the growth of new neurons and cell survival, enhancing memory and learning, and increasing molecules that are involved in the plasticity of the brain," Chaddock said.
Rather than relying on second-hand reports of children's physical activity level, the researchers measured how efficiently the subjects used oxygen while running on a treadmill.
"This is the gold standard measure of fitness," Chaddock said.
The physically fit children were "much more efficient than the less-fit children at utilizing oxygen," Kramer said.
When they analyzed the MRI data, the researchers found that the physically fit children tended to have bigger hippocampal volume about 12 percent bigger relative to total brain size - than their out-of-shape peers.
The children who were in better physical condition also did better on tests of relational memory - the ability to remember and integrate various types of information - than their less-fit peers.
The study appears in the journal Brain Research.