A study shows that many girls who used to be very sporty have fallen out of love with one another.
According to Women in Sport, body image, puberty and fear of judgement are some of the reasons.
The charity urges the sport, leisure and education sectors to work harder because it is a myth that girls drop sport simply because their priorities change.
Half of the people said they disliked being watched if they exercised, and seven in 10 avoided sport on their period.
It was a worry to feel self-conscious in sports gear.
One girl shared that her school has a lot of unisex clothes that are made for boys, when you are in puberty and have wider hips.
Even if there is no immediate threat and you are not around the boys, you still feel vulnerable.
Some said they didn't have the right body shape, while others disliked becoming hot and sweaty.
Some said that sport became too competitive as they grew older and they no longer felt able to join in just for fun.
Many people said making exercise more fun would motivate them.
It is an absolute travesty that teenage girls are being pushed out of sport at such a high rate.
Teenage girls are being pushed out of sport because of deep-rooted gender stereotypes.
We must all do more to reverse this trend and not accept that it is inevitable.
Kate Dale, from Sport England's This Girl Can campaign, said that the gender activity gap starts young.
By the time they are 16 and 17 years old, over two-thirds of teenage girls have stopped playing sport.
Many girls miss out on the physical, social and mental rewards of an active lifestyle when they grow up.
Positive experiences with physical activity at a young age are important for building healthy habits.
It is vital that girls see women and girls who look like them playing sport, to challenge the stereotypes of what women getting active should look like.
The studio you video library of workouts for teenage girls is free to all schools.