Scientists have already shown that physical activity can make you brainier.

If you want to boost your child's results at school, you could do a lot worse than ensuring that they do plenty of exercise.

But a team in America has used scans to show that an important part of the brain actually grows in children who are fit.

These youngsters tend to be more intelligent and have better memories than those who are inactive.

They believe that encouraging children to take exercise from a very young age could help them do better at school later.

They also tested the fitness levels of the children by making them run on a treadmill.

The scientists found that the hippocampus, a part of the brain responsible for memory and learning, was around 12 percent larger in the fitter youngsters.

Scientists also found that one of the most important parts of their brains was 12 percent larger than those of unfit youngsters.

Researchers from the University of Illinois, in the U. S., studied the brains of 49 children aged nine and ten using a magnetic resonance imaging scan, a technique which provides very detailed pictures of organs and tissues in the body.

"If you get some lousy genes from your parents, you can't really fix that, and it's not easy to do something about your economic status. But here's something that we can do something about."

"We knew that experience and environmental factors and socioeconomic status all impact brain development," he said.

Professor who led the study said the findings had important implications for encouraging individuals to take part in sport from a young age.