Weight regulation and bone mass: a comparison between professional jockeys, elite amateur boxers, and age, gender and BMI matched controls

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The aim of this study was to compare bone mass between two groups of jockeys (flat: n=14; national hunt: n=16); boxers (n=14) and age, gender and BMI matched controls (n=14). All subjects underwent dual energy X-ray absorptiometry (DXA) scanning for assessment of bone mass, with measurements made of the total body, vertebra L2-4 and femoral neck. Body composition and the relative contribution of fat and lean mass were extrapolated from the results. Data were analysed in accordance with differences in body composition, in particular, height, lean mass, fat mass and age. Both jockey groups were shown to display lower bone mass than either the boxers or control group at a number of sites including total body bone mineral density (BMD) (1.019±0.06 and 1.17±1.05 vs. 1.26±0.01 and 1.26±0.06gcm(-2) for flat, national hunt, boxer and control, respectively), total body bone mineral content (BMC) less head, L2-4 BMD and femoral neck BMD and BMC (p<0.05). Regression analysis revealed that lean mass and height were the primary predictors of total body BMC, although additional group-specific influences were present which reduced bone mass in the flat jockey group and enhanced it in the boxers (R (2)=0.814). Reduced bone mass in jockeys may be a consequence of reduced energy availability in response to chronic weight restriction and could have particular implications for these athletes in light of the high risk nature of the sport. In contrast, the high intensity, high impact training associated with boxing may have conveyed an osteogenic stimulus on these athletes.