Postures inverse

Most fibers can be classified as slow-twitch (ST) or fast-twitch (FT). The latter have a shorter time to peak tension, shorten faster, and have a shorter relaxation time than the former, and are used for movements requiring high speed or power. ST fibers are used for sustained activity and control of posture. The speed of shortening is related to the ATPase activity of the myosin, while the twitch duration parameters are related to the extent of the SR, and so these two are not directly connected. However, fiber histology and myosin gene expression have some controlling influences in common, so that speed of contraction and twitch duration vary inversely. 

An inverse correlation between OA and osteoporosis has been demonstrated, and both men and women with OA have increased bone mineral density at numerous skeletal sites. This relationship may derive from the influence of body weight on both diseases, because heavy individuals have higher bone density as well as increased risk of OA. Despite their lower risk of osteoporosis, individuals with OA are not protected against fracture. OA patients tend to be less posturally stable and more likely to fall, so despite the higher bone density, their fracture rates are similar to those of patients without OA. 

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