The study also found that very few girls knew what sort of bra to wear, whether their bra was a good fit or how to avoid breast pain while exercising.
The study by researchers in the Research Group in Breast Health based at the University of Portsmouth is the first in the UK to examine the impact of breasts on school girls taking part in sport or exercise. More than 2,000 school girls, aged 11 to 17 years took part.
It is published in the Journal of Adolescent Health.
The researchers are now calling for breast education for all Britain's school girls.
Three-quarters of the girls surveyed had at least one concern about their breasts, including embarrassment when getting changed for sport, breast bounce during exercise and breast pain. Their concerns peaked at the age of 14.
More than half the girls said they never wore a sports bra, and nearly all of them told the researchers they wanted to know more about breast health and breast support.
Professor Joanna Scurr, who leads the research group, said: "Previous studies of adult women have shown time and again that the same concerns are directly responsible for women no longer taking part in sport or exercise.
"What makes this worse is, as scientists, we know proper breast support reduces or even eliminates the problems associated with breast movement during sport. All that is needed is better education, preferably at puberty for all girls."
It has been estimated that 90 per cent of 14-year-old girls in the UK do not do enough exercise to meet government exercise guidelines.
Professor Scurr added: "Puberty is undoubtedly a difficult time for children of both sexes, but more girls than boys drop out of sport around this age. Even for those who overcome their physical embarrassment or awkwardness, the bra marketplace can be overwhelming and confusing."
The research group is made up of researchers from three universities (Portsmouth, St Mary's Twickenham and Chichester). The group is internationally renowned for research on the biomechanics of the breast, and is responsible for more than half of all the scientific publications in the area.
Amanda Brasher is a member of the research group and is leading the project to raise awareness in schools.
She said: "The research showed that the more concerns school girls have about their breasts, the less they exercise. We want to keep as many girls as possible involved in sport and exercise. With the right education we can alleviate many of the girls' worries, reduce embarrassment and eliminate the breast as a barrier to sports participation."
Research by the group has shown that using the appropriate sports bra reduces breast pain for most women, regardless of breast size, and that many women are unaware that they are wearing a badly fitting bra or routinely purchase ill-fitting bras. Breasts change in size and shape throughout a woman's life.
Dr Nicola Brown, from St Mary's University Twickenham said: "It is surprising how few women are aware of which bra is right for them, and the importance of good breast support."
Other findings included:
- 15 per cent of the girls thought their breasts were too big to be able to exercise;
- those with larger breasts (D-cup plus) are more likely to opt out of sport and exercise than those with smaller breasts;
- Only 10 per cent always wore a sports bra when exercising;
- Even those who took part in a lot of sport, and always wore a sports bra, said they didn't know if their bra was the right fit for them;
- 87 per cent wanted to know more about breast health and support.
Studies have shown that breasts move during exercise by up to 21cms in a figure of eight pattern, causing pain for an estimated three-quarters of women. A sports bra can reduce breast movement by a similar amount for AA cup to G-cup breasts. If breast movement is not reduced, there is a risk of irreparably damaging the fragile Cooper's ligaments, resulting in breast sag.
Dr Jenny Smith, one of the authors and a chartered psychologist from the University of Chichester, said: 'It is important that we help reduce the barriers associated with participating in physical activity to help encourage behaviour change."
The researchers are appealing for funding to develop resources for schools to provide breast health education for their pupils.