Children who are fitter have more brain power, according to new research.
A study of eight to 11-year-olds found exercise boosted grey matter in nine different areas.
These were important for cognition, executive function and academic achievement, say scientists.
It is the first time the dramatic effect of physical activity on the structure of the brain has been identified.
The Spanish team believe it will have an influence on their performance in exams and, consequently, future career success.
A third of children in the UK are overweight or obese with a fifth afflicted even before they begin primary school.
Dr Francisco Ortega, of the University of Granada’s Sport and Health Institute in Spain, said the findings add to evidence exercise protects older people against Alzheimer’s disease.
His researchers found the children’s physical fitness, especially aerobic and motor ability, was directly linked to more neurons in specific areas of the brain known as the cortical and subcortical regions.
Aerobic fitness is the capacity to do exercise for a long time and efficiently.
In particular, this was associated with more grey matter in the premotor cortex, which is important for learning (imitation) and social cognition (empathy) as well as controlling movements.
This type of exercise also boosts the power of the the parahippocampal gyrus and hippocampus which controls memory.
It also affects the inferior temporal gyrus, which plays a role in remembering to recognize visual stimuli and the caudate nucleus which is involved in learning.
The study, published in Neuroimage was part of the ActiveBrains project and involved more than 101 overweight and obese children.
Dr Ortega said: ‘Our work aims at answering questions such as whether the brain of children with better physical fitness is different from that of children with worse physical fitness and if this affects their academic performance.
‘The answer is short and forceful: yes, physical fitness in children is linked in a direct way to important brain structure differences, and such differences are reflected in the children’s academic performance.’
‘To the best of our knowledge, no previous study has examined the association of physical fitness with gray matter volume in overweight or obese children using whole brain analyses.’