Endurance exercise events like marathons, ultra-marathons, and triathlons have become increasingly popular recreational activities and/or competitions over the last several decades. It has been established that men usually exhibit increased performance potential in such competitions, but present literature suggests that as race distances increase, female endurance exercise performance increases, and the performance “sex gap” decreases. This may be explained by females’ increased ability to metabolize lipids when carbohydrate stores are depleted through long bouts of exercise. Therefore, the purpose of this study was to determine if sex-specific differences in substrate metabolism and metabolic gene expression were associated with endurance exercise capacity (EEC). Male and female C57BL/6-NCrl were subjected to an EEC test on a motorized treadmill. Tissues and blood were harvested in mice immediately following the EEC. A cohort of sedentary, non-exercise male and female mice were used as controls. Females outperformed males on the EEC by ~25%. This was associated with significantly higher serum ketone bodies and fatty acids in females at the end of the EEC. In sedentary female mice, skeletal muscle triglycerides were significantly elevated. Gene expression analysis demonstrated significant upregulation of several genes involved in skeletal muscle fatty acid oxidation. The findings suggest that female mice have a higher endurance exercise capacity due to an increased ability to mobilize and utilize fatty acids for energy.
Health and Exercise Physiology