Muscle Oxygen Saturation Responses During Maximal and Submaximal Exercise According to SLC16A1 (MCT1) Gene Polymorphism in Long-Distance Runners: A Cross-Sectional Pilot Study

<b>Background:</b> Blood lactate concentration and muscle oxygen saturation (SmO₂) are widely used indicators of endurance performance, reflecting the balance between oxygen delivery and utilization during exercise. To date, no studies have examined how the rs1049434 polymorphism of the <i>SLC16A1</i> gene (the polymorphism) influences SmO₂ referenced to blood lactate thresholds in long-distance (LD) runners. This pilot study aimed to investigate the association between SmO₂ referenced to blood lactate concentration during maximal and submaximal exercise and the polymorphism in male collegiate LD runners. <b>Methods:</b> Overall, 15 Japanese male collegiate LD runners participated. Physiological parameters, including respiratory gas data, were measured during a graded incremental exercise test using the breath-by-breath method. SmO₂ was recorded from the right vastus lateralis muscle. Participants were genotyped for rs1049434, and comparisons were made between the AA genotype and T-allele carriers (AT + TT genotype). <b>Results:</b> Runners with the AA genotype exhibited significantly higher %V·O_2max at the lactate threshold (<i>p</i> = 0.044) and at the onset of blood lactate accumulation (OBLA) than T-allele carriers (<i>p</i> = 0.023). For SmO₂ measurements, those with the AA genotype displayed shorter t1/2_{reoxygenation} (<i>p</i> = 0.043) and higher SmO_2max (<i>p</i> = 0.045). Furthermore, SmO₂-OBLA was significantly higher in the AA genotype than in T-allele carriers (<i>p</i> = 0.029). <b>Conclusions:</b> These findings suggest that runners with the AA genotype may have greater oxygen utilization efficiency and potentially improved muscle oxygen delivery during high-intensity exercise. However, these are preliminary results, and further studies with larger and more diverse cohorts are needed to confirm these observations.