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==Background==
===Physiology===
*Bone remodeling a continuous process where osteoclasts resorb old bone and osteoblasts form new bone. In microgravity, this balance is disrupted, leading to increased resorption and decreased formation. Weight-bearing bones, such as the hips and spine, are most affected due to the lack of gravitational stress.
*Calcium balance can be calculated as the difference between dietary intake and fecal and urinary excretion

==Clinical Features==
*In a six month’s duration, total body mineral density loss averages:<ref>Grigoriev AI, Oganov VS, Bakulin AV, Polyakov VV, Voronin LI, Morgun VV, Schneider VS, Marachko LM, Novikov, VE, LeBlanc AD, Shackelford LC. Clinicophysiological evaluation of bone changes in cosmonauts after long-term space missions. Aerosp Environ Med (Russia) 1998; 32(1):21–25.</ref>
**Pelvis - 12%
**Lumbar spine - 6%
**Femoral neck -8%
*There is significant variability with bone loss and most astronauts do no fully preflight density<ref> Harm DL, Jennings RT, Meck JV, Powell MR, Putcha L, Sams CP, Schneider SM, Shackelford LC, Smith SM, Whitson PA. Genome and Hormones: Gender differences in physiology. Invited review: Gender issues related to spaceflight: A NASA Perspective. J Appl Physiol 2001; 91: 2374–2383</ref>

==Differential Diagnosis==
{{Space medicine}}

==Management==
===Mission countermeasures===
*Weighted exercise although often peformed do not inhibit spaceflight associated bone loss
*Pharmaceuticals:
**Bisphosphonates - inhibit osteoclastic resorption but do not prevent muscle function declines

===Postflight bone mineral density rehab===
*Depending on mineral loss percentages and affected regions, astronauts undergo progressive weight exercises
**Spine: deadlifts and squats
**Calcaneal: Heel raises
**Femoral trochanter: Foot centered shallow single-leg press
**Femoral neck: squats
**Hips: Jump exercises

==Disposition==

==See Also==
*[[Space medicine]]

==External Links==

==References==
<references/>

[[Category:Space Medicine]]