A Combination of Soy Isoflavone and L-Carnitine Improves Running Endurance in Mice

The present study aimed to investigate the effect of APIC, a mixture containing soy isoflavone and L-carnitine on running endurance. Male C57BL/6 mice were orally administered APIC for 8 weeks. The APIC group exhibited a significant increase in treadmill running time until exhaustion compared to the control group. The respiratory exchange ratio in the APIC group was lower, indicating an enhancement in fatty acid oxidative metabolism. Furthermore, APIC supplementation increased the proportion of oxidative myofibers. Biochemical parameters associated with endurance capacity were also affected by APIC, as evidenced by increased muscle ATP levels and decreased levels of muscle triglycerides and blood lactate. qPCR and immunoblot analysis of C2C12 myotubes and gastrocnemius muscles indicated that APIC treatment stimulated AMPK signaling, mitochondrial biogenesis, and fatty acid metabolism. Additionally, treatment with APIC led to an increased oxygen consumption rate in C2C12 myotubes. Collectively, these findings suggest that APIC supplementation enhances mitochondrial biogenesis, promotes a switch from glycolytic to oxidative fiber types, and improves fatty acid metabolism through the activation of the AMPK signaling pathway in murine skeletal muscle. Ultimately, these effects contribute to the enhancement of running endurance.