Development of novel calibration model(s) to predict whole-body density in professional football players

Introduction: Questions continue to be raised about the validity that is in existence to estimate D_b, in professional male footballer players. Methods: Phase 1: n = 28 anthropometric variables were used on n = 206 footballers, using regression analyses to determine standard error of estimate and R ². A cut-off correlation coefficient set at r = 0.950 and 90% R ². Phase 2: all variables (z-scores, (Formula presented.) = 0.0, SD = ±1.0) to help reduce heteroscedasticity, β, r, t, significance of t and P-values were calculated. Phase 3: a forced stepwise–backwards regression analysis approach with nine predictors which met the acceptance criteria (r = 0.950, R ² = 90% and β weights) was used to develop a ‘best fit’ and a ‘practical’ calibration model. Phase 4: cross-validation of the two newly developed calibration method using LoA. Results: The ‘best fit’ model SEM (0.115 g ml⁻¹), the highest R ² (6.6%) (P ≤ 0.005), whereas the ‘practical’ calibration model SEM (0.115 g ml⁻¹), R ² (4.7%) (P ≤ 0.005) with r values = 0.271 and 0.596 and R ² (%) coefficients = 0.3526 for the ‘best fit’ and ‘practical’ calibration models, respectively (P = 0.01). Conclusions: The two calibration models supported an ecologically and statistically valid contribution and can provide sound judgements about professional footballers’ body composition.