The aim of the current study is to analyze the interaction of the muscle and bone system (muscle-bone unit) during puberty in males and females by computed tomography of the nondominant forearm. The data presented here are the first results from 318 healthy children (159 boys and 159 girls), aged 6-22 yr, and 336 adults (parents) participating in the DONALD Study (Dortmund Nutritional and Anthropometric Longitudinally Designed Study). Cortical area (CA) of the radius representing bone strength and muscle area (MA) representing muscle strength were measured with peripheral quantitative computed tomography (XCT 2000; Stratec, Pforzheim, Germany). A single slice measurement at a site corresponding to 65% of the ulnar length proximal to the radial endplate was used. MA and CA of the radius have been determined by a built-in software algorithm using density differences. There was a strong correlation between MA (x) and CA (y) in all children, adolescents, and adults (y = 0.019x + 10.93; r(2) = 0.77). Before puberty, boys and girls displayed a similar relation between MA and CA. CA in relation to MA was greater in girls than in boys during puberty. Analysis of covariance was performed investigating the dependency of CA on MA, five pubertal stages, sex, and interaction of sex and pubertal stages. MA representing muscle strength was the strongest predictor of CA (P < 0.001) representing bone mass. Pubertal stage (P < 0.001) and interaction of pubertal stage*sex (P = 0.002) also had a significant influence on CA. r(2) of the model was 0.85. These data suggest that in pubertal girls and women rather than in pubertal boys and men an additional factor shifts the relationship between MA and CA to higher values of cortical area. The present data confirm previous studies of the influence of puberty and estrogens or related factors on the muscle-bone interaction.
