Assessment Of Bone Strength At Differentially-loaded Skeletal Regions In Adolescent Middle-distance Runners

Abstract

Bone adaptations to loading extend beyond mineral accrual to geometric markers of bone strength. Available technology and regional differences in cortical bone dictate how bone strength is reported. Examination of bone strength at two differentiallyloaded skeletal sites using hip strength analysis (HSA) and bone strength index (BSI) is under explored in adolescent sporting populations. PURPOSE (i) to examine HSA at the femoral neck and BSI at the distal tibia between adolescent middle-distance runners and age- and gender-matched controls (ii) to examine factors predictive of HSA and BSI within each gender. METHODS Four groups of 20 adolescents (n = 80) (age range 14–18 years) comprised of male and female middle-distance runners, and male and female controls. To calculate distal tibial BSI, a region of interest representing 10% of tibia length was analysed using dual x-ray absorptiometry (DXA)-derived bone mineral and was combined with bone geometry and biomechanical properties from magnetic resonance imaging assessments. Calculations for femoral neck strength were acquired from DXA-derived HSA software. RESULTS Female athletes displayed greater distal tibial BSI than controls (p=0.002) but femoral neck bone measures did not differ. In males, no group differences were found at the distal tibia or femoral neck. In females, the strongest predictors of distal tibial BSI were hours of physical weekly activity and total muscle cross-sectional area (CSA) (58.3%), and neck of femur CSA accounted for 64.6% of the variance in a marker of femoral neck HSA. In males, total muscle CSA explained 43.5% of variance in BSI at the distal tibia, and femur length and neck of femur CSA explained 33.4% of variance at the femoral neck. CONCLUSIONS Exposure to similar high training loads may advantage female adolescent athletes, more than male adolescent athletes compared with less active peers in bone strength at the distal tibia.