Intended for healthcare professionals

Education And Debate

ABC of sports Medicine: Osteoporosis and Exercise

BMJ 1994; 309 doi: (Published 06 August 1994) Cite this as: BMJ 1994;309:400
  1. R L Wolman

    Dual energy x ray absorptiometry (DEXA) measurement of bone density.

    Exercise affects the skeleton in several ways. The direct effect of stress loading can be to increase bone mineral density, and this is now being considered as a strategy to prevent osteoporosis. Intensive aerobic exercise, however, can adversely affect bone density indirectly by its effect on the hypothalamic-pituitary-gonadal axis, which leads to a fall in blood oestrogen concentrations. This article discusses these effects.

    For 100 years it has been known that bone tissue adapts to the stress loads to which it is exposed. During the past 20 years bone densitometry has made it possible to assess the effects of physical activity on the skeleton. Bone densitometry measures the calcium concentration within bone. Several methods are used to measure bone density: the most popular is dual energy x ray absorptiometry (DEXA) because it gives a highly reproducible result and exposes patients to only small amounts of radiation. It uses a pencil-thin beam of x rays that scan over a skeletal site to a detector on the opposite side of the patient. From this, an estimate is obtained of the calcium concentration of the scanned bone.

    Factors that increase bone density

    Gravity (weight bearing)

    Low levels of physical activity lead to a fall in bone density. Complete bed rest gives a negative calcium balance within a few days and a detectable reduction in bone density within a few weeks. This detrimental effect emphasises the importance of early mobilisation after acute illness or operation. The lack of gravity stimulation is thought to be responsible for the losses seen in the gravity free environment of astronauts. Though regular exercise is associated with an increase in bone density, this benefit is less pronounced if the exercise does not incorporate gravity stimulation. Thus swimming, being a weight supported activity, produces only a limited effect …

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