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 Db, 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, (x) = 0.0, SD = +/- 1.0) to help reduce heteroscedasticity, beta, 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 beta 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 R2 (%) 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.