[Physical exercise prevents osteoporosis]

Life expectancy lengthened over the past 165 years. This is one of the reasons, that the prevalence of diseases connected with elderly, including osteoporosis, has increased. A physical activity may be used as prophylactic tool against osteoporosis and improve the skeletal resistance to bone fractures. Mechanotransduction, eg. the response of the cell to mechanical stimuli in bones is particularly relevant, because the mammalian skeleton remodels to adapt to loading environment. It also helps to gain and maintain the maximal BMD. The molecular mechanism of mechanotransduction is complex and depends on integrated activity of osteoblasts and osteocytes. Osteocytes are the cell that posses the ability to sense mechanical load. Shear stress induced in bones canaliculi by fluid flow induces the synthesis of PGE2, NO and activation of integrins, what triggers the Wnt signaling pathway. This pathway is important in osteocytes to prevent apoptosis and transmit the signals to other bone cells, and in osteoblasts for differentiation, proliferation and synthesis of bone matrix. The effectiveness of physical training in osteoporosis prevention depends on strain magnitude, strain rate, cycle number, strain frequency and rest periods, and the increase in BMD is found only in loaded parts of skeleton.