scores on intelligence tests．That was the finding of a study of teenage males in Norway．Now，other research shows that physical activity may help students do better in their classes .

　　The research comes as educators in some countries are reducing time for activities like physical education．They are using the time instead for academic subjects like maths and reading．The studies appeared between 2007 and 2017．They included more than 55，000 children，aged 6 to 18．

　　Amika Singh：“Based on the results of our study，we can conclude that being physically active is beneficial for academic performance. There are，first，Physiological explanations，like more blood flow, and so more oxygen to the brain．Being physically active means there are more hormones(荷尔蒙)produced like endorphins(内啡肽)．And endorphins make your stress level lower and

　　your mood improved, which means you also perform better.”

　　Also，students involved in organized sports learn rules and how to follow them．This could improve their classroom behavior and help them keep their mind on their work．

　　The study leaves some questions unanswered，however．Ms．Stash says it is not possible to say whether the amount or kind of activity affected the level of academic improvement．This is because of differences among the studies .

　　Also．they were mostly observational studies．An observational study is where researchers do not do controlled comparisons．They only describe what they observe．So they might observe a link that students who are more active often have better grades．But that does not necessarily mean being active was the cause of those higher grades．

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