González-Haro, C, Soria, M, Vicente, J, Fanlo, AJ, Sinués, B, and Escanero, JF. Variants of the solute carrier SLC16A1 gene (MCT1) associated with metabolic responses during a long-graded test in road cyclists. J Strength Cond Res 29(12): 3494–3505, 2015—Variants of the solute carrier SLC16A1 gene have been associated with alterations in MCT1 expression, because of a lactate (La−) transport deficiency across the cell membrane and a blood La− accumulation. The aim of this study was to associate the allelic and genotypic frequencies of 1470T>A, 2917(1414) C>T, and IVS3-17A>C variants relative to the blood La− kinetics and metabolic responses to a progressive effort until exhaustion. Twenty-five well-trained road cyclists performed a long-graded laboratory test: 10 minutes at 2.0 W·kg−1, first step at 2.5 W·kg−1 with increments of 0.5 W·kg−1 every 10 minutes until exhaustion. Blood La−, nonesterified fatty acids (NEFAS), and glucose levels were measured; fat and carbohydrate oxidation rates were estimated through stoichiometric equations. Three variants of SLC16A1 gene were determined for each subject, which were divided in two groups: wt (wild type)/mt (mutated type) and mt/mt genotype group versus wt/wt genotype group. Metabolic responses were compared between both groups with an unpaired Student's t-test; Friedman and Wilcoxon tests were performed for nonparametric data. The statistical significance was set at p ≤ 0.05. For 1470TA polymorphism, no significant blood La− differences were found between groups. 2197(1414)C>T allele carriers and IVS3-17A>C carriers showed significantly higher blood La− levels, lower blood NEFAS, and glucose levels at submaximal intensities. These findings open a new perspective to investigate SLC16A1 variants (1470TA and IVS3-17A>C) on La− deficiency transport and its regulation/interaction with other metabolic pathways. Future studies would be needed to clarify whether 1470T>A, 2917(1414)C>T, and IVS3-17A>C allelic/genotypic distribution benefit performance in endurance athletes.