Assessment of Countermovement Jump Performance in Collegiate Baseball Athletes: A Longitudinal Multilevel Modeling Approach

ABSTRACT: Burke, AA, Saine, ND, King, EL, Fields, JB, Jagim, AR, Miller, AD, Green, BC, and Jones, MT. Assessment of countermovement jump performance in collegiate baseball athletes: A longitudinal multilevel modeling approach. J Strength Cond Res XX(X): 000-000, 2026-Given the length and demands of the collegiate baseball season, monitoring body composition and neuromuscular performance can help optimize load management and athlete readiness. Relationships between body composition and countermovement jump (CMJ) performance were examined during a competitive baseball season. Pitchers and position athletes (n = 32) completed pre- and post-season dual-energy x-ray absorptiometry scans and weekly CMJ testing. Countermovement jump variables included jump height (JH), reactive strength index modified, peak braking force (PBF), and peak propulsive force (PPF), all normalized to body mass (BM). Repeated-measures multivariate analyses of variance assessed time and group (pitcher vs. position player) effects. Pearson correlations evaluated associations between CMJ and body composition metrics, and hierarchical linear models (HLMs) quantified individual performance trajectories. Preseason-to-postseason reductions were observed in BM, fat free mass (FFM), JH, and PPF (p < 0.05). Peak braking force declined in pitchers, while PPF declined across both groups. Body composition showed negligible correlations with CMJ metrics, except for a moderately negative correlation between JH and body fat percentage (r = -0.52, p < 0.001). Hierarchical linear models revealed curvilinear CMJ performance trajectories (p < 0.001), with position players exhibiting lower PBF throughout the season (β = -1.47, p = 0.03) and preseason FFM positively predicting PBF (β = 0.118, p = 0.010). Findings suggest that reductions in lean mass and force output occur across the competitive season and vary by position. It is recommended that practitioners implement routine longitudinal monitoring when using CMJ and body composition assessments, as they may assist in detecting neuromuscular fatigue and guide individualized training interventions.