Activity builds better bones in girls

High levels of physical activity may build stronger bones in teenage girls, an Australian study suggests.

Australian Catholic University (ACU) researcher David Greene compared the musculoskeletal health of 40 male and female adolescent middle-distance runners with a control group of 40 relatively inactive teenagers.

Using magnetic resonance imaging (MRI) scans and other techniques, he found the elite female runners had significantly greater bone strength than the controls.

The female athletes also showed much better bone density in the lower tibia, also known as the shin bone.

"While there were no differences in the boys ... in the female runners there were great differences, with the main weight-bearing bones stronger than in the normal population," said Dr Greene, who conducted the research for his PhD.

Athletes used in the study, supplied by the NSW Institute of Sport, trained an average 12 hours a week and competed at state and national levels in the 800m and 1500m events.

Teenagers in the control group exercised for around two hours per week.

Dr Greene, a university lecturer in exercise science, acknowledged a genetic predisposition for greater bone strength may have led to the girls becoming running champions.

But he suggested a combination of genes and physical activity was responsible for the female athletes' vastly superior bone density to the sedentary teenagers'.

"Our results support the theory that kids need to get out and get active in their formative years to accumulate as much bone as they can," Dr Greene said.

"Preferably the physical activity should be weight-bearing ... as studies have shown compromised bone health in swimmers and to a lesser extent, in cyclists."

Dr Greene, who presented his research findings recently at the third World Paediatric Bone Conference in Sorrento, Italy, said a person's opportunity to accumulate bone mineral stopped in the early 20s.

"The analogy of the bone bank is the easiest way to explain the process of bone developing during growth," he said.

"We slowly lose bone after our early 20s which accelerates in females around menopause.

"Therefore, the more bone you have in the bank, the greater the musculoskeletal retirement."