Background: Delayed-onset muscle soreness (DOMS) is a well-recognized barrier to training consistency among endurance runners, particularly in the 24–72 hours following high-intensity or prolonged running bouts. Branched-chain amino acids (BCAAs) leucine, isoleucine, and valine have been proposed to attenuate exercise-induced muscle damage (EIMD) and accelerate recovery; however, evidence in endurance-specific contexts is inconsistent.

Objective: To assess whether six-week BCAA supplementation (10 g/day) reduces DOMS severity, creatine kinase (CK) elevation, and subjective recovery ratings compared to placebo in recreational long-distance runners.

Method: A double-blind, placebo-controlled crossover trial was conducted with 40 recreational runners (22 male, 18 female; Mage = 28.3 ± 4.6 years; weekly mileage ≥ 40 km). Following a standardized downhill running protocol, DOMS (11-point NRS scale), serum CK, and Total Quality Recovery (TQR) scores were assessed at 24, 48, and 72 hours post-exercise during each arm. A four-week washout separated the two intervention periods. SPSS v.28 was used for statistical analysis. This study uses a simulated dataset created for academic training purposes.

Key Results: BCAA supplementation significantly reduced peak DOMS scores at 48 hours (5.1 ± 1.2 vs. 6.8 ± 1.4; p = 0.003) and lowered CK activity at 24 hours by 22.4% relative to placebo. TQR scores were significantly higher in the BCAA condition at 72 hours post-exercise (p = 0.018).