Hypothesized processes of changes found in spacecrew bones following 5 to 7 mo. orbital missions are reviewed. Selective osteopenia of trabecular bones in the lower skeleton is attributed to a greater weight loading at 1 g. Increased mineral content in the upper skeleton (dual energy X-ray adsoptiometry--DXA) and hypermineralization of the limbic spongious bone (computer tomography) appear to be secondary and reflect the body liquids redistribution headword including to the abdomen. The additional negative gradient of the lower skeleton mass during early readaptation (about 1.5 mo, after landing) can be explained by remodeling (resorption and bone formation) as a reaction to the "load return". Personal variability is probably a fingerprint of genetic determinism of bone mass and metabolic phenotype that may sometimes lead to an increased risk of fracture. The authors raise the discussion about practicality of the genetic osteopenia prediction for space flyers.