Transferable Vertical Jump Adaptations to Complex Training Across the Stretch-Shortening-Cycle Continuum in Adolescent Female Volleyball Players: A Bayesian Analysis

Background: Vertical jump performance is a key determinant of volleyball success. Prior evaluations of complex training in youth have relied largely on frequentist statistics, which are underpowered in the small, lean cohorts typical of elite youth sport. Objective: Apply Bayesian inference to evaluate vertical jump kinematics across short- and long-stretch-shortening-cycle modalities following a 9-week complex training program in adolescent female volleyball athletes. Methods: Eight athletes completed a periodized training protocol. Jump kinematics were assessed using a high-frequency force platform, and whole-body composition was assessed using bioelectrical impedance analysis. Data were analyzed using Bayesian inference. Results: Bayesian analysis indicated consistent improvements across jump modalities, with Block Volleyball Jump, Countermovement Jump, and Spike Jump heights increasing by 14.4%, 14.4%, and 13.9% (BF₁₀ = 24.3, 26.7, 38.4). Whole-body BIA detected no meaningful change in body mass (BF₁₀ = 0.37) or in muscle mass percentage (BF₁₀ = 1.67) over the intervention period. Conclusion: Complex training was associated with transferable neuromuscular improvements across the stretch-shortening cycle continuum. Bayesian inference provided an interpretable basis for evaluating training effects in a small elite cohort. The absence of a detectable change in whole-body composition is consistent with predominantly neural early-phase adaptation, although the single-arm design precludes causal attribution.