Children with healthy hearts and lungs have better grades, a new study has found. American researchers have found that physically fit boys and girls scored higher on reading and math.

“Cardiorespiratory fitness was the only factor that we consistently found to have an impact on both boys’ and girls’ grades on reading and math tests,” study co-author and Professor of Psychology Trent A Petrie, at the University of North Texas said.

“This provides more evidence that schools need to re-examine any policies that have limited students’ involvement in physical education classes,” Trent A Petrie added.

The researchers gathered data at five Texas middle schools from 1,211 students, of whom 54 per cent were girls with an average age of about 12.

While previous studies have found links between being physically fit and improved academic performance, this study also examined several other potential influences, including self-esteem and social support.

It also took into account the students’ socioeconomic status and their self-reported academic ability, Trent A Petrie, said.

In addition to cardiorespiratory fitness, social support was related to better reading scores among boys, according to the study. It defined social support as reliable help from family and friends to solve problems or deal with emotions.

“The finding that a larger body mass index for girls was related to better performance on the reading exam may seem counterintuitive, however past studies have found being overweight was not as important for understanding boys and girls performances on tests as was their level of physical fitness,” Trent A Petrie said.

The findings were presented at the American Psychological Association’s 120th Annual Convention.