A research team that had looked into a data comprising of 5461 girls between 11 to 15 yrs of age said that excess physical activity often makes these girls more prone to stress fractures.
The study shows that 16% of the participants take part in vigorous physical activity, which often lasts for 16 or more hours per week. These girls had a 1.88 times more risk of having a stress fracture than the girls doing physical activity for fewer hours per week. The study also showed that adolescent girls who worked out for less than 16 hours per week had more chance of engaging in disorderly eating practices to control weight gain.
For the girls who had vigorous activity for 16 or more hours a week, the chances of having a stress fracture is more for those who do running, gymnastics or even cheer leading.
Researchers point out that although physical activity is extremely beneficial for bone building, especially at adolescence, there is a threshold beyond which such kinds of activities can cause more harm than good. In fact adolescent girls seem to be more at risk from some form of rigorous activities than many others, as proved by the research.
Reference: Journal Pediatrics, issue April 2005