ABSTRACT
Bone mineral content (BMC), fat weight (FAT) and lean tissue weight (LTW) were determined by dual-energy X-ray absorptiometry (DEXA) in 20 young adults of both sexes who were performing habitual exercise. From these data, body weight, lean body weight (LBW) and the percentage of BMC relative to LBW (BMC%LBW) were obtained. First, body density based on a two-component model (D<SUB>2</SUB>) was calculated using the values of FAT and LBW of the subjects and the fat and lean densities of the Reference Body, Then percentage body fat (%Fat<SUB>2</SUB>) was calculated using the formula of Brozek et al. The body density for a three-component model (D<SUB>3</SUB>) was then determined from the values of FAT, BMC and LTW of the subjects, and the fat, bone mineral and lean tissue densities of the Reference Body. Percentage body fat (%Fat<SUB>3</SUB>) was also calculated in the same manner as %Fat<SUB>2</SUB>. Analysis of the data indicated that (1) females had higher values of BMC%LBW than males, and that (2) subjects whose %Fat<SUB>2</SUB> exceeded %Fat<SUB>3</SUB> by more than 1% were exclusively females whose BMC%LBW values were more than 6.1%. In contrast, those whose %Fat<SUB>2</SUB> was lower than %Fat<SUB>3</SUB> by less than -1% were exclusively males who had BMC%LBW values less than 5.2%. It is concluded that male subjects develop their muscles more than their bones with habitual exercise, which results in a lower BMC%LBW value than in females, and that for those with BMC%LBW values exceeding 6.1% (females) or less than 5.2% (males), %Fat calculation from body density using the formula of Brozek et a1. will produce an error of more than 1% if BMC%LBW is not considered.
ABSTRACT
We studied the relationship between bone mineral density (BMD) and history of habitual exercise in a group of university students comprising 41 athletes (27 males and 14 females) and 39 non-athletes (24 males and 15 females), ranging in age from 18 to 28 years. Their athletic history during elementray, junior and senior high schools was surveyed. Subjects who had engaged in athletic activities more than 3 days/week for more than two years at each school level were classified as a former physically active group, whereas the others were classified as controls. The BMD of the femur (femoral neck, Ward's triangle, trochanteric region) and vertebrae (L2-4) was ieasured using dual-photon absorptiometry with a <SUP>153</SUP>Gd source. The following results were obtained: 1) University athletes showed significantly higher BMD of the femur and L2-4 than non-athletes. 2) No significant difference was found for either sex between the physically active group on elementary school days and the control group with regard to BMD of the femur and L2-4. 3) The BMD of the femoral neck and trochanteric region in the male physically active group on junior high school days was significantly higher than that in the control group. The BMD of the femoral neck in the female physically active group on junior high school days was significantly higher than that in the control group. 4) The BMD of the femur and L2-4 in the female physically active group on senior high school days was significantly higher than that in the control group, whereas no difference was found between these two groups for males. These results suggest that regular exercise during puberty is effective for increasing BMD, especially in females. The finding that increased BMD in association with physical activity on senior high school days was observed only in females may be due to the synergistic effect of estrogen and exercise.