Bone Density Does Not Necessarily Measure Bone Strength

The greater the force you put on your bones during exercise, the stronger they become. Researchers at the University of Missouri in Columbia showed that recreational runners have denser bones than cyclists (Journal of Metabolism, February 2008). Another study from Université de St-Etienne in France show that youth soccer players have an increase in bone density over three years of playing high level soccer (Joint Bone Spine, January 2008). They failed to show that the soccer players had denser bones than their classmates, yet their intuition told them that heavy forces on bones while playing soccer must strengthen bones, so they stated that "The yearly gain in bone density is greater in soccer players than in controls."

These studies and many others comparing various sports measure bone density, not bone strength. The only way to measure bone strength is to see how much force it takes to break them. Needless to say, nobody is doing these studies in humans. So scientists use bone density, which can be measured, as a substitute for measuring bone strength. Nobody has shown that bone density determines bone strength. For example, birds have bones that are not dense because they need a low weight to fly effectively. Yet their bones are very strong. I think that, in the future, methods will be developed to determine bone strength and they will show that measuring bone density is, at best, a crude measure of whether a person is likely to break his or her bones. More