MECHANICAL LOADING REGIME AND ITS RELATIONSHIP TO BONE-MINERAL DENSITY IN CHILDREN

This study tested the hypothesis that differences in mechanical loadin g regime was important when evaluating the potential role of physical activity on bone density in children. Seventeen children competing reg ularly in weight-bearing sports producing loads of at least 3 times bo dy weight (Impact Load) were matched for race, gender, stage of pubert y, body weight, and average daily training time with children involved in competitive swimming (Active Load). Bone mineral density (BMD) was measured using dual photon absorptiometry at the lumbar spine (L2-L4) and femoral neck (FN), Tanner staging was used to assess puberty, die t was evaluated based on 3-d dietary records from two occasions, and a questionnaire assessed average daily nonweight-bearing hours. There w ere no significant differences in age (13.2 +/- 0.4 and 12.6 +/- 0.4), height (154.9 +/- 2.9 and 157.6 +/- 3.0), or weight (43.6 +/- 2.7 and 44.5 +/- 2.2) between Impact and Active Load groups. Impact Load chil dren had significantly greater FN BMD (0.78 +/- 0.02) than Active Load children (0.72 +/- 0.02) and a tendency for greater BMD L2-L4; 0.70 /- 0.03 and 0.66 +/- 0.03, respectively. These data indicate that chil dren involved in sports producing significant impact loading on the sk eleton had greater femoral neck bone density and a trend for greater s pinal bone density, than children in sports producing loads to bone pr imarily through muscular contraction.