INFLUENCE OF ACTIVITY LEVEL ON PATELLAR ULTRASOUND TRANSMISSION VELOCITY IN CHILDREN

Optimum development of both bone mass and bone quality during childhoo d is crucial in prevention of osteoporosis, a condition in which fract ures occur late in life. Increasing physical activity is one modality that shows promise for augmenting bone mass and improving bone archite cture in adults. Although a positive association has been reported bet ween physical activity and bone densitometry measurements in children, no studies have reported the relationship between physical activity a nd ultrasonic transmission in bone in children. The purpose of this st udy was to determine, in a cross-sectional sample of children, whether self-chosen levels of physical activity are associated with variation in apparent velocity of ultrasound (AVU). The convenience sample incl uded 65 third-and fourth-grade girls and boys from a rural Midwestern county of the United States. AVU was measured with the Signet (Osteo-T echnology, Cambridge, MA), Physical activity was determined with the T riTrac-R3D Ergometer (Hemo-kinetics, Madison, WI). A significant negat ive correlation (r = -0.54; p = 0.0007) was found between the girls' a ctivity and their AVU values. Stepwise regression analysis indicated a ctivity to be the strongest predictor of AVU in girls, accounting for 28% of the variance (p=0.0005). Weight also was a significant predicto r, accounting for an additional 13% of the variance (p = 0.00001). We conclude that more active prepubertal girls have lower AVU values than less active girls. This negative correlation between activity and AVU is curious, especially since other studies have found a positive rela tionship between activity and bone density in children. We speculate w hether a lag in development of bone quality might result in excessive microdamage in more active children. Further studies are needed to tes t this hypothesis.