MODERATE EXERCISE DURING GROWTH IN PREPUBERTAL BOYS - CHANGES IN BONEMASS, SIZE, VOLUMETRIC DENSITY, AND BONE STRENGTH - A CONTROLLED PROSPECTIVE-STUDY

Cross-sectional studies of elite athletes suggest that growth is an op portune time for exercise to increase areal bone mineral density (BMD) , However, as the exercise undertaken by athletes is beyond the reach of most individuals, these studies provide little basis for making rec ommendations regarding the role of exercise in musculoskeletal health in the community, To determine whether moderate exercise increases bon e mass, size, areal, and volumetric BMD, two socioeconomically equival ent schools were randomly allocated to be the source of an exercise gr oup or controls, Twenty boys (mean age 10.4 years, range 8.4-11.8) all ocated to 8 months of 30-minute sessions of weight-bearing physical ed ucation lessons three times weekly were compared with 20 controls matc hed for age, standing and sitting height, weight, and baseline areal B MD. Areal BMD, measured using dual-energy X-ray absorptiometry, increa sed in both groups at all sites, except at the head and arms. The incr ease in areal BMD in the exercise group was twice that in controls; lu mbar spine (0.61 +/- 0.11 vs. 0.26 +/- 0.09%/month), legs (0.76 +/- 0. 07 vs. 0.34 +/- 0.08/month), and total body (0.32 +/- 0.04 vs. 0.17 +/ - 0.06%/month) (all p < 0.05), In the exercise group, femoral midshaft cortical thickness increased by 0.97 +/- 0.32%/month due to a 0.93 +/ - 0.33%/month decrease in endocortical (medullary) diameter (both p < 0.05), There was no periosteal expansion so that volumetric BMD increa sed by 1.14 +/- 0.33%/month, (p < 0.05), Cortical thickness and volume tric BMD did not change in controls, Femoral midshaft section modulus increased by 2.34 +/- 2.35 cm(3) in the exercise group, and 3.04 +/- 1 .14 cm(3) in controls (p < 0.05). The growing skeleton is sensitive to exercise, Moderate and readily accessible weight-bearing exercise und ertaken before puberty may increase femoral volumetric BMD by increasi ng cortical thickness, Although endocortical apposition may be a less effective means of increasing bone strength than periosteal apposition , both mechanisms will result in higher cortical thickness that is lik ely to offset bone fragility conferred by menopause-related and age-re lated endocortical bone resorption.