Tennis playing initiated before puberty leads to greater skeletal benefits in peri-pubertal boys than girls when training is maintained

<b>Introduction</b>: The purpose of the study was to compare the exercise-induced changes in bone mass and geometry between boys and girls.<br /><br /><b>Methods</b>: Eighty competitive tennis players (43 boys, 37 girls) aged 7–19 years participated. Pubertal status was self-assessed using Tanner stages (TS 1–5). The dominant and nondominant humeri were compared for DXA-derived bone mass (BMC) and MRI-derived bone geometry [total bone area (TA), medullary area (MA) and cortical bone area (CA)]. <br /><br /><b>Results/Discussion</b>: Exercise-induced side-to-side differences in BMC, TA and CA were significant from TS1 to 5 in boys and girls (<i>p </i>< 0.06). Pre-pubertal (TS1) girls and boys show similar side-to-side difference in BMC after adjustment for training volume (19% vs. 15%, ns). Similar findings were found forTA and CA. In contrast, during puberty (TS2-4) boys displayed greater side-to-side differences than girls for BMC (27% vs. 18%, <i>p </i>< 0.05), TA (13–15% vs. 8%, <i>p </i>< 0.05) and CA (32% vs. 20%, <i>p </i>< 0.01), even after adjustment for tennis history. Girls partly compensated for the lack of an exercise-induced increase in bone size by a reduction of the medullary cavity on the dominant side (−5.5 to −13%, <i>p </i>< 0.05). In post-puberty (TS 5 or postmenarche), the size of the medullary cavity remained smaller on the dominant side in girls (−5% to −9%, <i>p </i>= 0.1–0.05??) whereas no such reduction was observed in boys. <br /><br /><b>Conclusion</b>: Regular exercise initiated before puberty and maintained throughout puberty leads to greater skeletal benefits in peri-pubertal boys than girls for bone mass and bone size, two of the major determinants of bone strength.<br />