[Exercise increases bone mass in children but only insignificantly in adults].

Data supporting the notion that exercise during growth built a stronger skeleton is compelling. Exercise during growth, especially during the pre-pubertal years, increases bone mineral density (BMD) and perhaps also bone size, each independently conferring bone strength. In adulthood, exercise at best halts bone loss or increases BMD by a few percentage points, an increase of questionable biological significance. High lifelong work load and high leisure time activity level are associated with high BMD. The Achilles heel of exercise is its cessation. Most BMD benefits achieved by exercise during growth are lost with cessation of exercise. Exercise at a lower level, after a period of high intense activity, may retain residual BMD benefits into old age. A reduced rate of fragility fractures in the population could perhaps be achieved by promoting a physically active lifestyle with lifelong high activity level during work and leisure time, leading to high BMD and fewer fractures.