The health of British girls is suffering because they shun school sports, rejecting them as overly competitive and un-feminine.
A survey of just over 1500 pupils revealed that only 12 per cent of girls are reaching the standard level of fitness by 14 - half the rate for boys, which is itself alarmingly low at 24 per cent.
More than half (51 per cent) of the girls said they had been put off exercise at school because of negative experiences of sport and PE lessons. Most admit they are not as physically active as they would like to be - but want a wider range of activities to be put on the timetable, such as dance and martial arts.
One 12-year-old told researchers: "I think sport is better for boys - they can go out and play football. If girls go out and play, they think they are tomboys. I think also girls get sweaty and don't like it."
A 14-year-old added: "We wanted to go out and have a fun game with friends but all we get is shouted at and being forced to do it. They try to make it very competitive."
In the survey, carried out by the Institute of Sport at Loughborough University for the Women's Sport and Fitness Foundation (WSFF), 45 per cent of girls said sport at school was "too competitive" and 48 per cent said being sweaty was "not feminine". A third of the boys interviewed said girls who were sporty were not very feminine.
The report shows at 8 or 9, both sexes are doing similar amounts of physical activity. By 10 and 11, girls are doing considerably less activity than boys.
The report recommends that girls should be offered single-sex sporting opportunities and that schools should set the target of 100 per cent participation in physical activities.