Physical activity, especially jumping, is known to increase bone strength. So why do young figure skaters get bone fractures? Changes occur in the outer layer of bone when the bone is subjected to repeated strain. These bone reactions are actually tiny breaks called stress fractures. In this study, researchers compared the bone density of female skaters who had stress fractures to that of healthy, nonathletic girls of the same age.
The researchers discovered that stress fractures in young skaters were not caused by low bone mass. Skaters had normal bone density compared to other girls their age who did not skate. However, skaters with stress fractures had much lower bone mass than skaters without fractures. It seems that stress fractures may be caused by extreme forces placed on normal bone.
What accounts for the range in bone density among young skaters? Researchers looked at the number of hours trained, age training began, type of training, body size, menstrual history, and calcium intake. They found that higher bone density occurs when girls master their first double jumps before age 10.
Differences in fracture rates were not based on when the girls learned single jumps. How quickly girls progressed from single to double jumps seemed to be the most important factor. This may be related to the fact that skaters without fractures exercised more hours per week. Perhaps this increased training time enabled the skaters to progress faster.
Skaters who practiced double jumps had the highest bone density. The greater impact on landing of a double jump compared to a single jump is the key to bone strength. Additionally, the landing leg had significantly greater bone mass than the take off leg.
These findings will help with injury prevention in young skaters. Skaters who do not start double jumps until after age 10 or 11 must progress slowly. They may not be able to handle the greater impact of jumping at first. Exercises to strengthen both the take off and the landing leg should begin when skaters start to learn jumps. These exercises are especially important as skaters moves from single to double jumps.