[Human bone system in microgravity: review of research data, hypotheses and predictability of musculoskeletal system...

The results of long-standing investigations of the human bone system in the piloted Mir and International space station missions were reviewed. The noninvasive DXA technology was used to determine bone mass (BM) and body composition. Predictable BM losses in the lower body tubular bones during 5 to 7-mo. space missions are characteristic of rapid but recoverable osteopenia and viewed as functional adaptation to altering mechanic loading of the skeleton. These changes feature high individual variability. Interestingly, the extent of BM changes in different segments of the skeleton displays stability in individual crew members irrespective of space station design. No strong dependence of BM changes on flight duration has been established and, therefore, calculation of the probability of critical bone demineralization after 1.5 to 2 years in space flight is impractical. Still less is the possibility to predict impairment of the bone structure which, together with BM losses, preconditions the risk of fracture. The data presented witness DXA inadequacy for such prediction. Main areas of researches toward optimization of the exploration mission design and planning in the context of the skeleton mechanic function maintenance are considered.