IANAD. I don't really know what causes bone-repair mechs to shut down in older women (I personally always thought that osteoperosis in old women was caused by less dense bones than men and losing a lot of their calcium to developing babies). However, I can provide some insight into low gravity issues.
In plain old exercise on earth, there are a wide variety of things that can be done to keep oneself in shape. One thing that is good to do are exercises which keep the bones strong. Things like cycling are great cardiovascular (heart and lungs) exercise, but do nothing for bone health. The issue is that bone healthy exercise is weight bearing exercise. In cycling, the bicycle supports too much of the rider's weight for it to benefit bone health. Things like weight lifting are bone healthy exercises. Just like muscles which atrophy if you don't use them, so will bones. You body has a funny way of adapting to be just as strong as it needs to be. In zero G, you skeleton has very few stresses on it, so it only stays as strong as it needs to.
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IANAD. I don't really know what causes bone-repair mechs to shut down in older women (I personally always thought that osteoperosis in old women was caused by less dense bones than men and losing a lot of their calcium to developing babies). However, I can provide some insight into low gravity issues.
In plain old exercise on earth, there are a wide variety of things that can be done to keep oneself in shape. One thing that is good to do are exercises which keep the bones strong. Things like cycling are great cardiovascular (heart and lungs) exercise, but do nothing for bone health. The issue is that bone healthy exercise is weight bearing exercise. In cycling, the bicycle supports too much of the rider's weight for it to benefit bone health. Things like weight lifting are bone healthy exercises. Just like muscles which atrophy if you don't use them, so will bones. You body has a funny way of adapting to be just as strong as it needs to be. In zero G, you skeleton has very few stresses on it, so it only stays as strong as it needs to.