Conclusion
Caffeine ingestion (3–13 mg · kg–1 body mass)
prior to exercise increases performance during
prolonged endurance cycling and running in the
laboratory. Caffeine doses below 9 mg · kg–1gen-
erally produce urine caffeine levels below the
IOC allowable limit of 12mg·ml–1. Moderate
caffeine doses (5–6 mg · kg–1) may also increase
short-term intense cycling performance (ª4–7
min) in the laboratory and decrease 1500-m
swim time (ª20 min). These results are generally
reported in well-trained or recreational athletes,
but field studies are lacking to confirm the
ergogenic effects of caffeine in the athletic world.
The mechanisms for the improved endurance
have not been clearly established. Caffeine inges-
tion generally increases resting venous plasma
FFA concentration and reduces muscle glycogen
use and increases muscle TG use early during
endurance exercise, suggesting greater fat oxida-
tion and reduced CHO oxidation in the working
muscles. However, a single metabolic explana-
tion for the ergogenic effect of caffeine is unlikely,
especially at low caffeine doses that do not cause
major metabolic changes. All human perfor-
mance studies have been unable to separate the
central effects of caffeine from peripheral effects.
Therefore, a central contribution to the enhance-
ment of endurance exercise performance follow-
ing caffeine ingestion is a strong possibility.
Potential mechanisms for improved perfor-
mance during short-term intense exercise
include direct caffeine effects on the CNS and/or
ion handling in skeletal muscle and increased
anaerobic energy provision in muscle. Definitive
research into the mechanisms of the ergogenic
effects of caffeine in exercising humans is ham-
pered by the ability of this drug and its by-
products to affect both central and peripheral
processes.
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