The condition of bone may be improved by exercise as it responds to mechanical stresses. These mechanical stresses usually take the form of skeletal muscle pulling at their points of attachment being their origins and insertions. Where these mechanical stresses are applied, most it has been shown that more mineral salts are deposited and more collagenous fibres are produced. Therefore, both the density and size of bone in these areas may be increased and these changes in bone structure are stimulated by increased loads being placed on the skeleton.
This has been borne out by greater bone mass being observed in weight lifters than in other lighter endurance athletes such as joggers. Other examples include racquet players who have been shown to have greater bone density in their playing arms. It has even been shown that if a leg is immobilised by being placed in plaster, due to a fracture, that even after a few weeks the bone becomes decalcified from lack of mechanical stress.
Whilst it may therefore be considered beneficial to utilise exercise to maintain healthy bones, great care must be taken with children whose bones and muscles are still developing. They should not be subjected to forms of sport involving high degrees of mechanical stress, partly because of the weaknesses that still exist within the bones, and also because of adverse effects on the development of these bones before maturity.
There are two main effects on bones as we grow older. Bones begin to lose calcium and this is one of the factors contributing to the condition called osteoporosis. Secondly, with age less protein is produced which alters the make-up of bone and sometimes creates brittle bones.
