TYPE OF PHYSICAL-ACTIVITY, MUSCLE STRENGTH, AND PUBERTAL STAGE AS DETERMINANTS OF BONE-MINERAL DENSITY AND BONE AREA IN ADOLESCENT BOYS

The present study was conducted to evaluate the influence of different types of weight-bearing physical activity, muscle strength, and puber ty on bone mineral density (BMD, g/cm(2)) and bone area in adolescent boys. Three different groups were investigated. The first group consis ted of 12 adolescent badminton players (age 17.0 +/- 0.8 years) traini ng for 5.2 +/- 1.9 h/week. The second group consisted of 28 ice hockey players (age 16.9 +/- 0.3 years) training for 8.5 +/- 2.2 h/week. The third group consisted of 24 controls (age 16.8 +/- 0.3 years) trainin g for 1.4 +/- 1.4 h/week. The groups were matched for age, height, and pubertal stage. BMD, bone mineral content (BMC, g), and the bone area of the total body, lumbar spine, hip, femur and tibia diaphyses, dist al femur, proximal tibia, and humerus were measured using dual-energy X-absorptiometry. When adjusting for the difference in body weight bet ween the groups, the badminton players were found to have significantl y higher BMD (p < 0.05) of the trochanter and distal femur compared wi th the ice hockey players despite a significantly lo,ver weekly averag e training. The badminton players had higher BMD compared with the con trol group at all weight-bearing BMD sites, except at the diaphyses of the femur and tibia and lumbar spine. The independent predictors of b one density were estimated by adjusting BMC for the bone area in a mul tivariate analysis among all subjects (n = 64). Accordingly, the bone density of all sites except the spine was significantly related to mus cle strength and height, and the bone density of the total body, neck, trochanter, distal femur, and proximal tibia was significantly relate d to type of physical activity (beta = 0.09-0.33,p < 0.05). The bone a rea values at different sites were strongly related to muscle strength and height and less strongly related to the type of physical activity and pubertal stage. In conclusion, it seems that during late puberty in adolescent boys the type of weight-bearing physical activity is an important determinant of bone density, while the bone area is largely determined by parameters related to body size. The higher BMD at weigh t-bearing sites in badminton players compared with ice hockey players, despite significantly less average weekly training, indicates that ph ysical activity including jumps in unusual directions has a great oste ogenic potential.