BACKGROUND:Quantifying the link between an athlete’s body composition (BC) and frame size (FS) to performance can lead to greater efficacy in training, performance development, and injury risk management. An example is the Muscle Bone Ratio (MBR). Two methods exist in measuring BC and FS in athletic populations, and thus calculating MBR: 1) dual X-ray absorptiom- etry (DXA), and 2) kinanthropometric (KA) measurements. This study explored 1) the validity of DXA and KA methods in determining MBR, and 2) MBR correlation to NFL Combine performance metrics in elite American football players. METHODS:Elite American football players attending Exos Combine programs (2021-2023) were assessed through DXA and KA methodology. Performance data included Max Broad Jump (cm), Max Bench Reps, and 0-40 yard sprints (s). Bland-altman statistical analysis and linear regression using Concordance Correlation Coefficent (CCC) were conducted for method com- parison in lean mass (kg), bone mass (kg), and MBR. The utility of MBR to performance was assessed through regression analysis and support vector machines (SVM). Principle Component Analysis (PCA) and agglomerate hierarchical cluster- ing (AHC) were conducted for all BC, FS, and performance variables for possible MBR replacements.RESULTS:285 athletes were assessed, 120 of which had complete DXA, 112 complete KA, and 159 complete performance data. Lean mass comparison resulted in a mean difference of +30.60 (kg), CCC of 0.2 (p<0.05). Bone mass comparison resulted in a mean difference of -6.68 (kg), CCC of 0.03 (p<0.05), with distinct negative systematic differences between methodolo- gies. MBR comparison resulted in a mean difference of +15.59, CCC of 0.00 (p>0.05). MBR to performance resulted in no distinct relationship and no statistically significant correlations at p>0.05. PCA revealed 84% of BC/FS variance can be described in the first three dimensions, with lean mass (kg), bone mass (kg), and femur breadth (cm) being the largest contributors. AHC consistently linked PCA results to performance variables.CONCLUSIONS:DXA and KA methods of quantifying BC and FS are systematically different, and cannot be used interchangeably. MBR had no significant correlation to performance, revealing flaws in utility within highly variant elite athletic populations such as American football. Further investigation would be required to develop and validate a new metric using PCA and AHC results.

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