Force vs. impulse: assessing the applicability of dynamic strength indices in individualized training recommendations

In this cross-sectional investigation, we aimed to compare impulse-derived (iDSI) and forcederived (fDSI) dynamic strength indices to determine their consistency in guiding individualized training recommendations. It also assessed the agreement between training prescriptions based on these indices and analyzed individualized neuromuscular profiles through case study comparisons. Twenty male skeleton and bobsled athletes performed countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) assessments in a counterbalanced order. Wilcoxon signed-rank tests were conducted to examine differences between fDSI and iDSI. Spearman correlation coefficients quantified intra-group relationships, and linear regression analysis evaluated the model fit between indices. Cohen's kappa (κ) was applied to assess agreement in training classifications derived from fDSI and iDSI. Both indices showed limitations in representing lower-limb neuromuscular function (Z = -3.72, p < 0.01, large effect). A moderate correlation was observed between iDSI and fDSI (rs = 0.47, p < 0.05), with moderate agreement in their training recommendations (κ = 0.52, 95% CI: [0.38, 0.66]). Case-study analyses revealed substantial inter-athlete variability in CMJ force-time characteristics, highlighting the need for individualized interpretation within performance profiling. Incorporating phase-specific, multi-metric evaluations of force-time variables may improve the precision of training decisions and better inform athletespecific programming.