Separating Mechanical Reconstruction from Predictive Information in Countermovement-Jump Height: Force–Time Organization and Rectus Femoris Tensiomyography in Elite Youth Soccer Players

High countermovement-jump (CMJ) height prediction may reflect mechanical reconstruction rather than independent neuromuscular information. This study separated mechanically proximal variables from mechanically restricted force-expression, movement-organization, and tensiomyography (TMG) predictors. Sixty-six elite youth football players completed force-platform CMJ and rectus femoris TMG assessments. Jump height was reconstructed from mean propulsion force and propulsion duration. After excluding these variables and direct mechanical equivalents, Ridge, Elastic Net, GAM, and random forest models were evaluated using repeated nested cross-validation, with predictor-set, ablation, and held-out permutation-importance analyses. The mechanical benchmark almost perfectly reconstructed jump height (RMSE = 0.0027 m; predictive R2 = 0.998). After mechanical restriction, random forests were the strongest prespecified single model family (RMSE = 0.0510 m; predictive R2 = 0.296), whereas the fully nested one-standard-error model-selection pipeline provided a more conservative estimate of generalization (RMSE = 0.0548 m; predictive R2 = 0.187). Within the retained predictor set, movement organization provided more information than force expression (predictive R2 = 0.214 vs. 0.078). The TMG-only prediction was worse than the mean-level benchmark (predictive R2 = −0.039), and adding TMG did not improve the CMJ base model. CMJ height is readily reconstructed from proximal propulsion mechanics. After their removal, movement organization retains modest predictive information, whereas single-muscle rectus femoris TMG did not provide useful standalone or incremental value in this cohort.