Vertical Jump Changes Across the Stretch-Shortening-Cycle Continuum Following Complex Training in Adolescent Female Volleyball Players: A Single-Arm 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 can be difficult to interpret in the small cohorts typical of 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 = 29.7, 27.2, and 126.9, respectively), with peak power increasing in parallel for all three jumps (BF10 = 22.8, 23.1, and 37.6). Whole-body Bioelectrical Impedance Analysis (BIA) detected no meaningful change in body mass (BF10 = 0.34) or in muscle mass percentage (BF10 = 1.56) over the intervention period. Conclusions: Complex training was associated with increases in jump height across modalities representing different points on the stretch-shortening-cycle continuum. Bayesian inference provided a complementary probabilistic basis for evaluating training-related change in a small cohort. No accompanying change in whole-body composition was detected by BIA; because muscle architecture was not assessed and the design was single-arm without a control group, the mechanism underlying the jump-height changes cannot be determined.