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Donald A. Bailey and Alan D. Martin

A considerable amount of research into osteoporosis has focused on the management and treatment of bone loss in later life. More recently, a limited amount of research has been directed toward the development of an optimal level of peak bone mass during the adolescent and early adult years. While genetics is a major determinant of bone status, there is considerable evidence that physical activity is an important nonhereditary factor. Studies on adults suggest that the positive effect of physical activity on bone is modest in the short term but may be quite powerful with more intense activity that overloads the muscular system for a longer time period. In children, however, our knowledge about the long-term effects of physical activity on bone accretion is incomplete. This paper presents a review of the pediatric literature dealing with the relationship of physical activity to bone mineral density status in the adolescent population.

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Timothy R. Ackland, Peter W. Henson and Donald A. Bailey

The effect of the uniform density assumption upon estimation of body segment inertial parameters was examined by employing directly measured, CT-derived, and cadaver-derived density values. Sectional and average density values for the right leg segments of a patient 29 years of age and a cadaver (65 years) were obtained with a GE 9800 computed tomography scanner using dual energy radiographic factors of 80 kV, 200 mAs, and 140 kV, 200 mAs. Careful sectioning of the cadaver leg following these scans permitted mass and density measurements to be directly performed. The results for both legs showed marked variation in cross-section density values throughout their lengths, which highlighted the limitations of the assumption of uniform segment density. The effect of employing this assumption was tested using a series of inertial parameter estimation strategies by means of mathematical modeling. Adoption of the uniform density assumption when estimating inertial parameters of the human leg segment was shown to produce only minor errors. However, greater errors were shown to be caused by inaccurate estimates of segment volume.

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Robert G. McCulloch, Donald A. Bailey, Robert L. Whalen, C. Stuart Houston, Robert A. Faulkner and Bruce R. Craven

This cross-sectional study compared differences in os calcis bone density and distal radius bone mineral content (BMC) among adolescent soccer players, competitive swimmers, and control subjects. Sixty-eight males and females (23 soccer players, 20 swimmers, 25 controls) ages 13 to 17 served as subjects. The results for os calcis trabecular density indicate a trend that may be of clinical significance and that may warrant further study. The swimmers had the lowest os calcis density in both sexes whereas the soccer players had the highest bone density at this weight-bearing site (F=2.54, p<.08). No differences with respect to distal radius BMC were observed among activity groups or between sexes.