Longitudinal bone mineral density changes in female child artistic gymnasts

Abstract

Changes in bone mineral density (BMD), and related factors, in female child artistic gymnasts (n = 9) and their age(±0.3 years), height- (±2.8 cm), and weight- (±1.7 kg) matched controls (n = 9) were prospectively examined. It was hypothesized that gymnasts would possess higher BMD at baseline, 6, and 12 months later and have greater gains in BMD over 1 year compared with controls. BMD (g/cm2) of the total proximal femur (TPF), Ward's triangle (WT), trochanter (Troch), femoral neck (FN), lumbar spine (LS, L1-L4), and total body (TB) were measured by dual-energy X-ray absorptiometry. Physical activity was measured by a 7-day recall; daily dietary intakes of energy and nutrients were estimated from 3-day records. Serum osteocalcin and urinary pyridimum cross-links were measured by radioimmunoassay and high performance liquid chromatography, respectively. Gymnasts versus controls possessed significantly higher BMD at all sites measured. Although not significantly different (p > 0.05), gymnasts compared with controls had moderately larger percentage changes in Troch (% Δ = 8.6 ± 3.0 vs. 3.8 ± 5.1%, d = 0.41), FN (% Δ = 6.1 ± 1.2 vs. 3.9 ± 1.6%, d = 0.55), LS (% Δ=7.8 ± 1.1 vs. 6.8 ± 1.6%, d = 0.26), and TB BMD (% Δ= 5.6 ± 0.8 vs. 3.4 ± 0.7%, d = 0.98) as evidenced by the magnitude of the effect sizes (d). Gymnasts versus controls possessed a lower percentage body fat (p < 0.01) and engaged in more hours of very hard activity (p < 0.0001). Calcium, as a percentage of adequate intake, decreased over 12 months (p < 0.01), and urinary cross-links significantly decreased over 6 months in both groups. Female child gymnasts possess higher BMD at the TPF and related sites, LS, and TB compared with nongymnast controls, and 1 year of gymnastics training moderately increases Troch, FN, LS, and TB BMD for gymnasts compared with controls. These findings lend support to the idea that gymnastics training in childhood helps maximize peak BMD.