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Bone is a dynamic tissue whose functional mass is controlled by the balance between the endocrine drive towards bone resorption and the mechanically-engendered drive towards bone formation. Strain is the key intermediate variable between loading forces and bone remodelling. Animal studies have shown that static loading of bone has no osteogenic effect; bone loss occurs as if there were no loading at all. However, dynamic loading, that is, cyclic change in internal strain, is strongly osteogenic, with relatively few cycles required for maximum effect. However, if a sufficient number of cycles is applied, repetitive loading can cause stress fractures. This number decreases as internal strains increase. Thus strain redistribution within bone, as caused by muscle fatigue or improper sports equipment, is a significant cause of fracture.

We compared areal bone mineral density (BMD) of the total body (TBMD), antero-posterior lumbar spine at L3 (APS), lateral spine at L3 (LS) and femoral neck (FN). In order to understand better the effect of gender-related size differences on BMD, we also compared the estimated volumetric BMD at L3 (VLS) and the femoral neck (VFN). Subjects were asymptomatic women (n = 22) and men (n = 44) with an age range of 58-79 years. BMD at each site was measured by dual-energy X-ray absorptiometry using a Hologic 2000 in array mode. Results of the statistical analyses (ANOVA) showed the men to have significantly greater BMD at all areal sites [APS, LS (p < 0.05); FN (p < 0.01); TBMD (p < 0.001)]. The two estimated volumetric comparisons, however, showed no gender differences. Results demonstrate how measures from areal BMD measures can be misleading when comparing groups of different size. In older men and women planar measures may overestimate gender differences in BMD.

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.

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