Effect of Lactiplantibacillus plantarum GKK1 Supplementation on Exercise-Induced Fatigue, Muscle Damage, and Recovery in Healthy Men: A Randomized, Double-Blind, Placebo-Controlled Trial

Background: Exercise-induced fatigue (EIF) and exercise-induced muscle damage (EIMD) impair neuromuscular performance and delay post-exercise recovery. However, human evidence regarding the structural and functional recovery kinetics following Lactiplantibacillus plantarum GKK1 supplementation remains limited. Objective: This randomized, double-blind, placebo-controlled trial investigated whether 4 weeks of L. plantarum GKK1 supplementation improves functional recovery and modulates biochemical responses after an EIMD protocol in healthy men. Methods: Forty-eight healthy men with no regular exercise habits were randomly assigned to receive either placebo (n = 24) or L. plantarum GKK1 (two capsules daily, totaling 1.0 × 1011 CFU; n = 24) for 28 consecutive days. The trial was registered at ClinicalTrials.gov (NCT06893549). After supplementation, participants completed 100 maximal plyometric jumps. Countermovement jump (CMJ), isometric mid-thigh pull (IMTP), and Wingate anaerobic performance were assessed before EIMD and at 3, 24, and 48 h post-EIMD. Blood biomarkers of muscle damage, inflammation, oxidative stress, endocrine response, and sympathoadrenal activity were analyzed, and urinary 3-methylhistidine and creatinine were measured. Results: Compared with placebo, GKK1 supplementation was associated with smaller post-exercise decrements in the CMJ rate of force development, relative peak force, jump height, IMTP relative peak force and peak RFD, and Wingate anaerobic performance (p < 0.05). GKK1 also attenuated post-exercise increases in CK, myoglobin, hs-CRP, and TBARS, and was associated with more favorable testosterone, HGH, catecholamine, and dopamine responses. At 24 h post-EIMD, urinary 3-methylhistidine and the 3-methylhistidine/urinary creatinine ratio were lower in the GKK1 group than in the placebo group. No adverse changes were observed in clinical safety biomarkers. Conclusion: These findings suggest that GKK1 may be a safe nutritional strategy to facilitate functional recovery, attenuate secondary inflammatory responses and modulate urinary markers associated with muscle breakdown following muscle-damaging exercise in healthy young men.