Capsaicin increases endurance capacity and spares tissue glycogen through lipolytic function in swimming rats

The influences of various doses of capsaicin on endurance capacity remain to be clarified. The purpose of this study was to determine whether or not capsaicin delays stored tissue glycogen depletion. Rats were orally given either a vehicle or a dose of capsaicin, 6, 10, or 15 mg/kg of body weight, 2 h before exercise. The rats in each group were divided into three subgroups for resting and swimming exercise (30 min, exhaustion). Swimming exercises were performed with a weight corresponding to 3% body weight attached to the tail, and the endurance capacity was evaluated by the swimming time until exhaustion. The 15 mg/kg dose of capsaicin significantly (p < 0.05) enhanced the endurance performance time and plasma concentration of epinephrine, norepinephrine, free fatty acid and glucose rose to significantly higher levels within 30 min; swimming exercise compared to rest (p < 0.05). At the 15 mg/kg capsaicin dosage. the plasma insulin level decreased to significantly lower levels in group subjected to 30-min swimming as compared to the resting group (p < 0.05), while plasma glucagon rose to a significantly higher level (p < 0.05). Liver and gastrocnemius muscle glycogen in the group subjected to 30-min swimming was maintained at significantly higher concentrations in the rats fed 15 mg/kg of capsaicin as compared to the vehicle counterparts (p < 0.05). These results suggest that the improvement in swimming endurance with the high capsaicin dosage is caused by an increase in fatty acid utilization as the energy source, resulting in the sparing of glycogen.