Inter-arm bone mass and size asymmetries in children tennis players are maturity status specific: a 9-month study on the effects of training time across pubertal change and somatic growth

Abstract Purpose Bone growth with exercise is best assessed by tennis-induced inter-arm asymmetries. Yet, the effects of training and maturation across puberty were unclear. This study explored arm bone growth across 9 months of training in 46 tennis players 7–14 years (25 boys, 21 girls). Methods Bone mineral content (BMC) and bone area (BA) were measured from DXA scans. Pubertal status was assessed by Tanner stage (TS) and somatic growth by maturity offset (MO). Children were grouped as pre- (TS I–I), early (TS I–II), and mid/late pubertal (TS II–III). Results Training time (TT) change in the three groups was 160–170, 190–230, and 200–220 h, respectively. Bone asymmetries were large in all groups ( d > 0.8, P < 0.001): 5–18 g (9–21%) and 9–17 g (17–23%) in girls and boys, respectively, for BMC, and 5–15 cm 2 (6–13%) and 9–15 cm 2 (12–15%) in girls and boys (10–13%), respectively, for BA. BMC and BA change asymmetry peaked at pre-puberty in girls (56%, 46%) and at early puberty in boys (57%, 43%). Asymmetry gains varied with baseline asymmetry (41%) and change in TT (38%) and TS (17%) in BMC, and with baseline asymmetry (58%) and change in MO (17%) and TS (12%) in BA. Conclusion All bone asymmetries were substantial. Tennis-induced bone gains were higher at pre- to early puberty in girls and at early to mid/late puberty in boys. Training enhanced mostly bone mass and maturity status enhanced mostly bone size; sex was not bone-change modeling impactful. Implications are discussed considering certain limitations.