Effect of Chronic Beta-Alanine Supplementation on Physical Performance and Lactate Markers in Elite Marathon Runners Living at Altitude: A Randomized Double-Blind Clinical Trial

This study aimed to evaluate the effect of chronic beta-alanine supplementation on physical performance and blood lactate markers in elite marathon runners living at altitude. A randomized, double-blind, placebo-controlled clinical trial with a pre–post intervention design was conducted. Twelve athletes residing at 3259–3399 m above sea level were randomly assigned to a beta-alanine group (6 g·day⁻¹; n=5) or a placebo group (n=6) for four weeks. Before and after the intervention, blood lactate markers and physical performance were assessed using a maximal incremental running test on a 400 m track. Linear mixed-effects models showed no statistically significant group x time effects for maximal lactate concentration (β = -1.29 mmol·L⁻¹; 95% CI: -4.81 to 2.23), post–rest lactate difference (β = -1.77 mmol·L⁻¹; 95% CI: -5.67 to 2.12), or lactate clearance percentage (β = -19.27%; 95% CI: -54.4 to 15.8). Similarly, no meaningful effects were observed for maximal sustained running speed (β = -0.15 km·h⁻¹; 95% CI: -2.12 to 1.82), total exercise time (β = -0.42 min; 95% CI: -2.51 to 1.67), or distance covered (β = -0.21 km; 95% CI: -0.79 to 0.36). In conclusion, four weeks of beta-alanine supplementation did not produce detectable improvements in physical performance or lactate markers in elite marathon runners living at altitude, with effect estimates indicating small and imprecise differences between groups.