Respiratory Muscle Warm-Up Improves Agility But Not Countermovement Jump Performance in Highly Trained Junior Female Volleyball Players: A Double-Blind Randomized Crossover Trial.

gKowalski, T, Grzechowiak, L, Gruszczyńska, O, Tosun, Mİ, and Szafraniec, R. Respiratory muscle warm-up improves agility but not countermovement jump performance in highly trained junior female volleyball players: A double-blind randomized crossover trial. J Strength Cond Res XX(X): 000-000, 2026-This study aimed to investigate the effectiveness of respiratory muscle warm-up (RMWU) in highly trained junior female volleyball players and to determine the optimal protocol for this population. Seventeen athletes completed a randomized crossover trial and performed 4 RMWU sessions. They included protocols with inspiratory resistance, expiratory resistance, combined inspiratory, and expiratory resistance, and a control session. Various respiratory indices, countermovement jump (CMJ), and Illinois Agility Test (IAT) performances were analyzed. The results were examined using analysis of variance with either between-protocol or time*protocol approach. The significance level was established as p < 0.05. Significant differences with large effect size were identified in IAT (F = 3.362, p = 0.026, and ηp2 = 0.174). After all RMWU protocols, IAT was performed faster compared with the control session (0.95-2.13%, depending on protocol). No significant differences were found for pre- and post-RMWU measurements of respiratory indices. Notably, differences in lung capacity between protocols were close to the significance threshold (p = 0.093) and the improvement after the expiratory protocol was the most substantial (12.0%). No significant effects were observed for any CMJ variable. Respiratory muscle warm-up, consisting of 1 set of 30 respiratory maneuvers at approximately 40% of maximal mouth pressures, tended to enhance agility performance, without significantly affecting respiratory variables or CMJ outcomes in highly trained junior female volleyball players. The combined protocol was most beneficial for IAT. Further research should explore RMWU with higher load and potential sex differences in response to RMWU, as studies in men typically report more favorable outcomes.