[Bone adaptation to mechanical loading].
BACKGROUND
In general, regular physical activity has a strong effect in promoting health and preventing diseases. Bone health is promoted through regular weight-bearing physical activity that uses muscular strength and power and exerts force on the skeleton above normal levels. Some theories have been advanced to explain the relationship between mechanical loading and the bone tissue's biological response. The aim of this review is to review some of these theories and discuss how bone adapts to mechanical loading.


METHODS
The literature was identified on Medline. In addition, relevant books were examined.


RESULTS
The mechanostat theory is widely accepted. It is based on the assumption that bone structure changes through a feedback system in which changes in peak mechanical strain drive bone cells to change bone structure. Other theories suggest that bone formation depends upon the number of strain cycles, strain distribution and strain rate, not only the strain magnitude as suggested in the mechanostat theory.


CONCLUSIONS
The magnitude of the loading, type of activity, the rate of the activity, and the number of repetitions seem to be important factors associated with the effect of physical activity on bone.
Torstveit
Monica Klungland
MK
Norges idrettshøgskole, idrettsmedisinsk seksjon Postboks 4014 Ullevål stadion 0806 Oslo. monica.torstveit@nih.no
D000222:Adaptation, Physiological / Q000502:physiology*; D001696:Biomechanical Phenomena; D016723:Bone Remodeling / Q000502:physiology*; D001842:Bone and Bones / Q000502:physiology* / Q000503:physiopathology; D012090:Cumulative Trauma Disorders / Q000209:etiology / Q000503:physiopathology; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008465:Mechanoreceptors / Q000502:physiology; D008954:Models, Biological; D016474:Weight-Bearing / Q000502:physiology*