Schoolgirls who avoid exercise are more at risk of becoming obese adults, according to a study published in the British Journal of Sports Medicine.

In a study of 800 children between seven and nine years old, girls are just half as sporty as boys with only 28 per cent exercising vigourously for 20 minutes, three times a week - which includes school activities such as PE lessons. For the boys, 53 per cent took part in physical activity.

Researchers at Trinity College in Dublin were surprised to see such gender differences in children so young, and believe the findings may explain why women find it harder to fight obesity as adults.