Author(s): RÖGNVALDSDÓTTIR, V., JOHANNSSON, E., STEFANSDOTTIR, R., Institution: UNIVERSITY OF ICELAND, Country: ICELAND, Abstract-ID: 266

INTRODUCTION:
Bone mineral density (BMD) during childhood is important for healthy bone development and is influenced by biological maturation, body composition and physical activity. This study examined the associations between skeletal maturity, body composition, sprint performance and talent identification rank with total body BMD in pre-adolescent female soccer players. A secondary aim was to explore the association between vitamin D supplementation and BMD.
METHODS:
A total of 108 female soccer players (mean age 11.90 ± 0.31 years) completed DXA assessments of bone mineral density and body composition, radiographic assessment of bone age and 40-m sprint testing. Talent identification rank (1–3) was assigned independently by coaches. BMD Z-scores were calculated using NHANES age-specific reference data. Group differences across ranks were examined using one-way ANOVA. Linear regression models tested predictors of BMD Z-score including skeletal age offset (BA–CA), fat-free mass index (FFMI), sprint speed and body fat percentage. A supplementary Welch t-test and regression model evaluated differences in BMD between vitamin D supplement users and non-users (n = 103).
RESULTS:
Players displayed a mean BMD of 0.95 ± 0.08 g/cm² and a mean BMD Z-score of 0.75 ± 1.07, with 95.4% classified as having healthy BMD. Rank 1 players had higher BMD Z-scores than Rank 3 players (1.11 ± 1.06 vs 0.20 ± 1.05), were faster and had lower body fat (all p < 0.01). In the primary regression model, BA–CA (β = 0.566, p < 0.001) and FFMI (β = 0.278, p < 0.001) were significant independent predictors of BMD Z-score, explaining 55.8% of the variance (adjusted R² = 0.545). Body fat percentage did not improve model fit and was not a significant predictor (p = 0.259). Rank 3 was associated with lower BMD compared with Rank 1 in an exploratory model (p = 0.007). Vitamin D supplementation was not associated with BMD in either the t-test (p = 0.955) or regression model (p = 0.906).
CONCLUSION:
Skeletal maturity and fat-free mass were the strongest predictors of BMD in pre-adolescent female soccer players, while sprint performance and body fat percentage did not independently explain BMD variation. Talent identification rank separated players in terms of BMD, sprint speed and body fat, although not in terms of skeletal maturity. Vitamin D supplementation showed no association with BMD. These findings underscore the importance of monitoring maturation and lean mass development in youth athletes, particularly during the years of rapid bone mineral accumulation.