Bone cross sectional geometry and bone strength in male athletes exposed to differential loading modalities and non-athletic controls: an advanced hip structural analysis study Running head: Femoral bone geometry in male athletes and controls

Loading of the skeleton can be achieved through weight-bearing exercise which is important for the development of a functionally and mechanically appropriate bone structure. Our objectives were to determine hip cross-sectional geometry in elite male athletes (n=54) subjected to different loading modalities (gymnastics, endurance running and swimming) and non-athletic, age-matched controls (n=20). Dual energy X-ray absorptiometry (iDXA, GE Healthcare, UK) measurements of the total body (for body composition) and the left proximal femur were obtained. The Advanced Hip Structural Analysis (AHA) programme was used to determine conventional areal bone mineral density (aBMD), hip axis length (HAL), crosssectional area (CSA), and cross -sectional moment of inertia (CSMI). Bone strength indices were derived using the femoral strength index (FSI) (Yoshikawa et al, 1994). Gymnasts and runners had significantly greater age, height and weight adjusted aBMD than swimmers and controls (p<0.05). Gymnasts and runners had greater resistance to axial loads (CSA) and runners had increased resistance against bending forces (CSMI), compared to swimmers and controls (p<0.01). Hip axis length was greater in controls and this group also had lower indices of bone strength (FSI) compared to gymnasts and runners (1.4 vs 1.8 and 2.1 respectively, p<0.005). Lean body mass correlated significantly with aBMD, CSA and FSI (r=0.365-0.457, p<0.01) and correlations were stronger in controls (r=0.657-0.759, p<0.005). Our findings suggest the importance of regular physical loading and lean mass for promoting bone density and bone structural properties. Further research examining the contribution of different loading modalities to specific skeletal geometrical properties would be of value to inform strategies directed at maximising bone strength and thus fracture prevention, through sport and exercise.