Oct 31 : Children who play vigorously for 20 to 40 minutes daily might be making their brains as well as their bodies stronger, shows a latest study that highlights why physical activities are essential for kids.

Researchers from the Medical College of Georgia in the US divided 163 overweight children aged seven to 11 into three groups and observed them for three months.

While the first group did no physical activity after school, the second group did 20 minutes of vigorous physical activity five days a week after school. The third group did 40 minutes of such activity on those same days, reported the online edition of USA Today.

The activity groups played intermittent, high-energy running games, such as flag tag, relays, jump rope and modified basketball. They wore heart-rate monitors and were rewarded for maintaining a high average heart rate.

Students also were given cognitive-function tests at the beginning and end of the study. They were tested for their mathematics and reading achievements and executive function.

Executive function includes skills important for planning and organizing, focusing on schoolwork, resisting impulses, self-monitoring and using strategies to achieve goals.

The scientists found that the children in the 40-minute activity group had significant improvement on an executive-function test compared with the other groups.

They increased about four points on a cognitive-performance scale. Those in the 20-minute group showed about half that improvement. There was a small improvement in mathematics achievement for both exercise groups but no signs of improvement in reading.

The researchers also performed brain scans and found that the children who were exercising appeared to have more neural activity in the frontal areas of their brains - an important area for executive function. Those in the exercise groups also lost about one to two percent of body fat.