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 are in existence to estimate Db, in professional male footballer players. Methods: Phase1: n = 28 anthropometric variables were used on n  =  206  footballers,  using  regression  analyses  to  determine  SEE and R2.  A  cut-off  correlation coefficient set at r = 0.950 and 90% R2. Phase2: all variables (z-scores,x= 0.0, SD = ±1.0) to help reduce  heteroscedasticity, β, r, t,  significance  of t  and P-values  were  calculated.  Phase3:  a  forced stepwise – backwards regression analysis approach with 9 predictors which met the acceptance criteria (r = 0.950, R2 = 90%, andβ weights) was used to develop a ‘best  fit’ and a ‘practical’ calibration model. Phase4: cross-validation of the 2 newly developed calibration method using LoA. Results: The ‘best fit’ model SEM (0.115 g ml-1), the highest R2 (6.6%) (P = < 0.005), whereas the ‘practical’ calibration model SEM (0.115 g ml-1), R2 (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 2 calibration models supported an ecologically and statistically valid contribution and can provide sound judgements about professional footballers’ body composition.