Individual responses to pomegranate juice on recovery from exercise-induced muscle damage in collegiate male volleyball players

Abstract

Background: Volleyball demands frequent explosive, stretch–shortening muscle actions that elevate the risk for exercise-induced muscle damage (EIMD) and delayed-onset muscle soreness (DOMS). Polyphenol-rich pomegranate juice (POMj) has been proposed to aid recovery, yet evidence in highly trained team-sport athletes is limited. This study investigated whether short-term POMj enhances functional and isokinetic recovery following an EIMD protocol in collegiate male volleyball players and identified individual responders using the smallest worthwhile change (SWC) method. Methods: Fourteen Tier-3 male collegiate volleyball players completed testing in a randomized, double-blind, placebo-controlled crossover design. The supplementation was 1000 mL of natural POMj (500 mL evening prior; 500 mL 2 h pre-EIMD protocol) or flavor-matched placebo (PLA). The EIMD protocol consisted of 200 weighted (10% body mass) maximal vertical jumps. The outcomes at baseline (BL) and 48 h post-EIMD included functional tests (vertical jump height, handgrip, medicine-ball throw, flexibility, wall-squat) and knee isokinetic/isometric contraction indices (extension/flexion at 30° s−1 and 180° s−1; MVIC at 45°). DOMS (VAS) was assessed at BL, 0, 12, 24, and 48 h. Repeated-measures ANOVA was used to test condition effects. The SWC was set to 0.2 × SD at BL to classify individual responders. Results: ANOVA revealed a significant main effect of time for most variables (p < 0.05), indicating recovery or changes across 48 h; however, no significant between-condition differences (POMj vs. PLA) were observed for any functional or isokinetic parameter. Although the knee extensor peak torque at 180° s−1 significantly improved from baseline within the POMj (p = 0.002), this recovery was not statistically superior to that of the PLA (p = 1.000). Similarly, DOMS increased significantly over time (p = 0.001), with no significant difference between conditions. SWC analysis revealed higher responder proportions with POMj for selected 180° s−1 indices (e.g. knee extensor relative peak torque (RPT): ~86% POMj vs. ~64% PLA; absolute peak torque (APT): ~79% vs. ~71%), indicating practically meaningful individual benefits despite null mean differences. Conclusions: In highly trained male volleyball athletes, short-term POMj did not outperform placebo on group-mean recovery outcomes at 48 h post-EIMD; however, SWC-based analyses showed a higher proportion of meaningful responders with POMj in selected high-velocity isokinetic measures, supporting responder-focused evaluations of recovery nutraceuticals in sport-specific settings.