Background: Body composition assessment is important in professional football as a measure of overall adaptation of the athlete to the training demand and calorie intake. However, it is operator-dependent, relying on subject positioning and the focus angle of the X-rays. In addition, the usual appendicular lean mass index (ALMI) does not include the pelvitrochanteric muscles, which are often implicated in athlete injuries. Methods: Three independent operators compared the reproducibility of dual-energy X-ray absorptiometry (DEXA) including pelvi-trochanteric muscle mass in twenty professional football players, using the standard and a new method. Results: Mean age, weight, and height of the footballers were 25.9 ± 4.9 years, 79.4 ± 9.4 kg, and 1.83 ± 0.09 m. Using the standard method, the ALMI was 9.28 ± 0.62, 9.20 ± 0.65, and 9.13 ± 0.64 kg/m2 for the first, second and third operator, respectively. When including the pelvi-trochanteric muscles, the ALMI values were 11.90 ± 0.66, 11.84 ± 0.63, and 11.83 ± 0.65 kg/m2 for the three operators. The difference between the two methods was significant (p < 0.001). The mean inter-operator difference was similar regardless of the method used (0.099 ± 0.06 kg/m2). The intraclass correlation coefficients (ICC) (A,1) were 0.949 [0.881; 0.979] for the standard method and 0.977 [0.951; 0.990] for the new method. The ICC (C,1) was 0.960 [0.918; 0.983] for the standard method and 0.979 [0.957; 0.991] for the new method. Conclusions: Thus, both new and conventional methods showed excellent reproducibility. However, reproducibility and inter-operator variability were better with the adjustment of the new scan lines. Moreover, the inclusion of a larger gluteal and adductors muscle mass was easy to achieve, providing additional information that could potentially be useful for early diagnosis and/or prevention of future muscular injuries in elite athletes.
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