Effects of Caffeine Ingestion on Utilization of Muscle Glycogen and Lipid During Leg Ergometer Cycling

Abstract

The purpose of this investigation was to study the sparing effects of caffeine on the utilization of muscle glycogen during 30 min of leg ergometer cycling (70% V̇O₂ max). A caffeine solution (250 ml; 5 ml/kg body weight) ingested 1 h prior to exercise (CAF trial) decreased the use of muscle glycogen by 42% (P < 0.025) in seven subjects when compared to a decaffeinated control trial (CON). There was a modest increase in serum FFA and muscle triglyceride use was 150% greater in the CAF as compared to the CON trial. Respiratory exchange during exercise also reflected a shift in carbon source from carbohydrate to lipid. Since known in vitro effects of caffeine include an increased use of muscle lipid and an inhibitory influence on Phosphorylase a, it is suggested that the ergogenic effects of caffeine on endurance performance are, in part, the result of direct actions in muscle rather than solely to enhanced mobilization, uptake, and oxidation of blood-borne FFA.