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Babies move in the womb to develop strong bones and joints, there are some molecular interactions that are stimulated by movement which guide the cells and tissues of the embryo to build a functionally robust yet malleable skeleton. If an embryo doesn’t move, it may be a sign of brittle bones or abnormal joints.
Cells in the early embryo receive biological signals that direct them to contribute to different types of tissue in different places. In the absence of embryonic movement the cells that should form articular cartilage receive incorrect molecular signals, where one type of signal is lost while another inappropriate signal is activated in its place.
Using chick and mouse embryos where movement could be altered, the scientists had previously shown that when movement is reduced the articular cells at the joint do not form properly, and that in extreme cases the bones can fuse at the joint. If movement is reduced bone and joint formation and development may be abnormal.
haleplushearty.org