The influence of caffeine on the utilization of skeletal muscle glycogen during exercise

Seven men were studied during 30 minutes of leg ergometer cycling at approximately 70% V02 max to determine the effects of caffeine ingestion on the utilization of muscle glycogen. A caffeine solution (250 ml; 5 mg/kg body weight) given one hour prior to exercise (CAF trial), decreased the rate of muscle glycogen depletion by 36 + 11.86% (p. .005) as compared to a decaffeinated control trial. During the CAF treatment, there was a 16% increase in serum FFA prior to exercise. Exercise resulted in a removal of FFA from the blood in both trials. Muscle triglyceride levels prior to exercise in the CAF trial were nearly 23% higher than control levels and suggest, that excess FFA present prior to exercise in the CAF trial were esterified into triglyceride. Subsequent post-exercise values indicated a greater utilization of endogenous lipid. A model based on caffeine's stimulatory effects on muscle lipid mobilization and its inhibitory action on muscle phosphorylase a appears to be responsible for the lessened use of muscle glycogen.