Individualized Z-Score Classification of Jump Load and Its Association With Countermovement Jump Performance Throughout a Division I Volleyball Season

ABSTRACT: Sanders, GJ, Stampley, J, Parker, B, Skodinski, S, and Peacock, CA. Individualized Z-score classification of jump load and its association with countermovement jump performance throughout a Division I volleyball season. J Strength Cond Res XX(X): 000-000, 2026-The countermovement jump (CMJ) is commonly used to assess neuromuscular performance, yet it remains unclear whether day-to-day deviations in jump-derived workload meaningfully influence next-day CMJ outcomes in volleyball. This study examined whether individualized z-score classifications, reflecting how daily Player Load and jump counts deviated from each athlete's typical workload, were associated with changes in next-morning CMJ performance across an NCAA Division I female volleyball season. Fourteen Division I female volleyball athletes (20.6 ± 1.1 years, 182.3 ± 8.2 cm) were monitored throughout a competitive season. External workloads were collected during all practices and matches, and CMJ performance was assessed using dual force plates. Z-scores were calculated for player load and low, medium, high, and total jump counts, then categorized as low (z < -0.5), moderate (-0.5 ≤ z ≤ 0.5), or high (z > 0.5). Z-score binning significantly differentiated workload exposure (P ≤ 0.045 for all), with large effect sizes for Player Load (ηp2 ≥ 0.17) and total jump counts (ηp2 ≥ 0.161) and other jump intensity count categories. By contrast, all CMJ variables including demonstrated trivial effect sizes (ηp2 < 0.015) and no significant differences across workload classifications. Correlations between workload z-scores and CMJ metrics were uniformly not significant (P ≥ 0.130). Individualized z-score classifications of jump-based workloads were not associated with next-day CMJ performance changes in Division I female volleyball athletes, suggesting typical in-season workload variation may be insufficient to disrupt neuromuscular status detectable by CMJ testing.