Effect of changes in weight-bearing exercise on lumbar bone mass after age fifty.

This two year longitudinal study of 40 healthy subjects over age fifty (27 exercisers, 13 non-exercisers) was designed to evaluate the impact of weight-bearing exercise on lumbar bone mineral density as assessed by quantitative computed tomography. In both males and females exercising at moderate levels, a high correlation was found between changes in exercise and changes in bone density (r = 0.78 and 0.91, respectively P less than 0.002). For extreme levels of exercise (greater than 300 min/week in females over age fifty, and greater than 200 min/week in males over age seventy) bone density was low, confirming earlier cross-sectional results. Subjects without change in their exercise levels and non-exercisers lost similar amounts of bone. Increasing body mass index was identified as a protective factor with regard to lumbar bone loss. We conclude that in exercisers continuation of weight-bearing exercise is mandatory to prevent excessive bone loss. Extreme levels of exercise may be detrimental to bone density in subjects over age fifty years.