Skeletal System: The skeletal system provides four basic functions:

Support for tissues and muscle
Protection for vital organs
Movement through bones and attached muscles
Storage for minerals and immature blood cells

Support: Bones and cartilage which make up the skeleton are the only rigid materials in the body. The 206 bones of the skeleton provide a framework and points of attachment for many of the soft tissues of the body. The five main classifications of bones are: Long (e.g. femur), Short (e.g. tarsal bones of the foot), Flat (e.g. frontal bone of the skull), Irregular (e.g. vertebrae) and Sesamoid (e.g. knee cap)

Protection: These structures protect some of the vital tissues and functional organs of the body. Typical examples are:

Skull - protects the brain
Vertebrae - protects the spinal cord
Thoracic cage - protects the heart and lungs

Movement: Bones act as levers during movement and provide solid structures to which muscles are attached. The joints allow movement between bones and these movements are directly related to the type of joint and range of motion. Joints fall into one of three categories: Fixed fibrous or Synarthroses (e.g. bones of the skull), slightly moveable or Amphiarthroses (e.g. symphysis pubis) and freely movable or Diarthroses.

Freely Movable joints comprises of four main groups: Ball and Socket (e.g. hip), Hinge (e.g. elbow), Pivot (e.g. radius and ulna) and Gliding (e.g. carpal joint of the wrist)

Storage: In some bones there is red marrow which produces red blood cells, some white cells and platelets. Minerals, especially calcium and phosphorous are also stored in bones and can be distributed to other parts of the body.

Effect of exercise on the skeletal system: 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 immobilized by being placed in plaster, due to a fracture, that even after a few weeks the bone becomes decalcified from lack of mechanical stress.