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, 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.

The characterisation of bone geometry in male and female athletes may increase our understanding of how physical loading may enhance bone strength in both sexes. This study investigated sexual dimorphism in hip geometry of athletes and age- and sex-matched non-athletes. Dual energy X-ray absorptiometry of the left proximal femur was performed in 62 male (n = 31; 30.2 ± 4.6 years) and female (n = 31; 27.9 ± 5.2 years) competitive endurance runners, and 36 male (n = 18; 28.7 ± 5.8 years) and female (n = 18; 29.1 ± 5.3 years) non-athletes. The hip structural analysis programme determined areal bone mineral density (aBMD), bone area (BA), hip axis length, cross-sectional area (CSA), and cross-sectional moment of inertia (CSMI) of the femoral neck. Strength indices were derived from the femoral strength index (FSI) (Yoshikawa et al., J Bone Miner Res 9:1053-1064, 1994). Despite similar size-adjusted aBMD, sexual dimorphism was apparent for BA, CSA and CSMI, with superior values in men compared to women (P < 0.01). FSI was greater in male and female athletes than non-athletes (P < 0.01). From all groups, results in male athletes inferred greatest resistance to axial (CSA) and bending loads (FSI). Estimates of bone strength (FSI) were greater in female athletes than male and female non-athletes, supporting the osteogenic value of regular loading of the hip.