LAUSR

Background/Objectives: Lactate (LA) is a key metabolite in exercise metabolism, transported across cell membranes by monocarboxylate transporters (MCTs). Although genetic variation in MCT genes has been linked to LA kinetics, evidence in athletic populations remains limited. This study investigated nine MCT1 polymorphisms (rs4301628, rs12028967, rs10857983, rs3789592, rs10776763, rs1049434, rs6537765, rs7556664, rs7169) in relation to LA metabolism. Methods: 337 Polish and Czech males (elite athletes, sub-elite competitors, physically active controls) performed two maximal Wingate tests. Buccal swabs were collected for DNA extraction and single nucleotide polymorphism (SNP) genotyping. LA was assessed before and after the tests. Results: Five variants (rs3789592, rs7556664, rs7169, rs1049434, rs6537765) remained significantly associated with LA measured 30 min after the second Wingate (LA30′) and delta clearance capacity (DCC) in elites (codominant and recessive models: p = 0.01–0.03; false discovery rate (FDR)-adjusted p = 0.02–0.04). Rs10776763 showed the broadest associations, surviving FDR for LA30′ in all models (p = 0.003–0.03; FDR-adjusted p = 0.01–0.03) and for LA accumulation capacity (ACC) in the recessive model (p = 0.01; FDR-adjusted p = 0.03). Rs12028967 also supported a clearance role, with LA30′ significant in elites (p = 0.004; FDR-adjusted p = 0.01) and DCC in the overall cohort (p = 0.02; FDR-adjusted p = 0.03). In contrast, rs4301628 and rs10857983 demonstrated isolated LA30′ effects in elites (p = 0.004–0.01; FDR-adjusted p = 0.01), and no production-phase endpoint other than rs10776763 survived FDR; ACC remained significant in the recessive model (p = 0.01; FDR-adjusted p = 0.03). Conclusions: The results suggest that MCT1 polymorphisms contribute to differences in LA metabolism and warrant replication in larger, more diverse cohorts.