Femur-bending properties as influenced by gravity: V. Strength vs. calcium and gravity in rats exposed for 2 weeks.

Growing bone material strength (S) can increase with gravitational intensity (g). That would be consistent with demineralization reported during space flight and reports that strength increases with mineral content. This study, however, shows an increase in material strength independent of calcium content (C). Male, Sprague-Dawley rats were exposed to chronic simulations of altered gravity from the 28th to 42nd d of age. Zero G was stimulated for 13 animals by harness suspension and 3 G for 30 animals by centrifugation. For fresh femurs, S as determined by bending and C as determined by AA spectrometry were compared with results for 11 harnessed, control animals and 13 normal, control animals. Multiple regression shows significant dependence of S (10(6) N.m-2) upon g (multiples of Earth's gravity, G) as independent from C (% by mass) for which there is no significant coefficient of partial regression: S = (62 +/- 1) + (7 +/- 1 g) + (0 +/- C).