Adaptation of bone to exercise
Bone is classified as a connective tissue and is unique in that it becomes mineralised (with calcium and phosphate ions) providing a rigid support structure. Bone is sensitive to changes in the forces placed on it and has the capacity for growth and regeneration if damaged. Exercise creates mechanical forces that cause deformation of specific regions of the skeleton and results in change.
In response to mechanical loading, osteoblasts (bone-forming cells) travel to the bone surface experiencing the strain and begin the process of bone remodelling. The osteoblasts secrete proteins and collagen, and deposits it between the bone cells increasing the strength in that area. These proteins form a criss-cross matrix between the bone cells, eventually becoming mineralised as calcium phosphate crystals (giving bone its rigidity).
The adaptation of bone to mechanical loading occurs at different rates in the axial skeleton and the appendicular skeleton, owing to different amounts of cancellous and compact bone. cancellous bone responds quicker to stimuli than compact bone. The bones of the vertebral column contains approximately 70% cancellous bone, whereas spongy bone is only found in the marrow cavities within long bones. Deposition of new collagen fibres in vertebral bone can be expected after 8 to 12 weeks of mechanical loading. Ensuing mineralization of the new bone matrix to give full strength to the new bone requires additional time and may take several weeks to months to complete.