Acute Effects of Isometric Contraction Distribution on Jump Performance in Volleyball Players

<b>Objectives:</b> This study evaluated how different distributions of isometric conditioning activity (ICA) durations affect countermovement jump (CMJ) performance in highly trained male volleyball players compared to a control condition (CTRL). <b>Methods:</b> Twelve participants performed CTRL and three ICA protocols in a half-back squat: 9 s (3 × 1 × 3 s), 27 s (3 × 3 × 3 s), and 45 s (3 × 5 × 3 s). CMJ height was measured before and at 3, 6, 9, and 12 min post ICA. <b>Results:</b> A two-way repeated measures ANOVA showed significant main effects of time (F = 3.820; <i>p</i> = 0.009) and condition (F = 6.451; <i>p</i> = 0.001), with no significant interaction (F = 1.484; <i>p</i> = 0.138). Post hoc analysis indicated significant CMJ height increases at 9 min [mean difference (MD) = 5.1 ± 0.6 cm; <i>p</i> = 0.045] and 12 min (MD = 6.0 ± 1.4 cm; <i>p</i> = 0.010) post ICA. Moreover, CMJ height was significantly greater in the 27 s (MD = 10.0 ± 0.6 cm; <i>p</i> = 0.002) and 45 s (MD = 7.3 ± 2.0 cm; <i>p</i> = 0.035) conditions compared to the 9 s protocol. <b>Conclusions:</b> Incorporating ICAs of 9 s or 45 s into warm-up routines can enhance CMJ performance, although these durations may elicit different neuromuscular adaptations and movement strategies.