Various investigators have postulated that increasing bone mass by 3-5 percent would reduce fracture risk by 20-30 percent. Our data in collegiate female gymnasts demonstrate hip and spine bone mineral density values of up to 40 percent above values in normal age-matched controls and elite runners, despite menstrual irregularities. Further, we have observed the dynamic response of bone to high-impact forces in gymnasts over the training season as bone increases of 2-5 percent.